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PubMed2005

Genome plasticity and ori-ter rebalancing in Salmonella typhi.

Genome plasticity resulting from frequent rearrangement of the bacterial genome is a fascinating but poorly understood phenomenon. First reported in Salmonella typhi, it has been observed only in a small number of Salmonella serovars, although the over 2,500 known Salmonella serovars are all very closely related. To gain insights into this phenomenon and elucidate its roles in bacterial evolution, especially those involved in the formation of particular pathogens, we systematically analyzed the genomes of 127 wild-type S. typhi strains isolated from many places of the world and compared them with the two sequenced strains, Ty2 and CT18, attempting to find possible associations between genome rearrangement and other significant genomic features. Like other host-adapted Salmonella serovars, S. typhi contained large genome insertions, including the 134 kb Salmonella pathogenicity island, SPI7. Our analyses showed that SPI7 disrupted the physical balance of the bacterial genome between the replication origin (ori) and terminus (ter) when this DNA segment was inserted into the genome, and rearrangement in individual strains further changed the genome balance status, with a general tendency toward a better balanced genome structure. In a given S. typhi strain, genome diversification occurred and resulted in different structures among cells in the culture. Under a stressed condition, bacterial cells with better balanced genome structures were selected to greatly increase in proportion; in such cases, bacteria with better balanced genomes formed larger colonies and grew with shorter generation times. Our results support the hypothesis that genome plasticity as a result of frequent rearrangement provides the opportunity for the bacterial genome to adopt a better balanced structure and thus eventually stabilizes the genome during evolution.

Evolution, Molecular↗

PubMed2001

Structure solution of the basic decagonal Al-Co-Ni phase by the atomic surfaces modelling method.

The atomic surfaces modelling technique has been used to solve the structure of the basic Ni-rich Al-Co-Ni decagonal phase. Formula Al70.6Co6.7Ni22.7, space group P10, five-dimensional unit-cell parameters: d1 = d4 = 4.752 (3) A, d2 = d3 = 3.360 (2) A, d5 = 8.1710 (2) A; alpha12 = alpha34 = 69.295 degrees, alpha13 = alpha24 = 45 degrees, alpha14 = 41.410 degrees, alpha23 = alphai5 = 90 degrees (i = 1-4), V = 291.2 (7) A5; D(x) = 3.887 Mg x m(-3). Refinement based on /F/; 2767 unique reflections (/F/ > 0), 749 parameters, R = 0.17, wR = 0.06. Describing the structure of quasicrystals embedded in n-dimensional superspace in principle takes advantage of n-dimensional periodicity to select the minimal set of degrees of freedom for the structure. The method of modelling of the atomic surfaces yielded the first fully detailed structure solution of this phase. Comparison with numerous former, less accurate models confirms several features already derived, but adds a new essential insight of the structure and its complexity. The atoms fill the space forming recurrent structure motifs, which we will (generically) refer to as clusters. However, no unique cluster exists, although differences are small. Each cluster shows a high degree of structural disorder. This gives rise to a large configurational entropy, as much as expected in a phase which is stable at high temperature. On the other side, the cluster spatial arrangement is perfectly quasiperiodic. These considerations, corroborated by analysis of the structural relationship with neighbouring periodic phases, strongly suggest the existence of a non-local, long-range interaction term in the total energy which may be essential to the stability.

Journal Article↗

PubMed2005

Comparative landscape genetics and the adaptive radiation of Darwin's finches: the role of peripheral isolation.

We use genetic divergence at 16 microsatellite loci to investigate how geographical features of the Galápagos landscape structure island populations of Darwin's finches. We compare the three most genetically divergent groups of Darwin's finches comprising morphologically and ecologically similar allopatric populations: the cactus finches (Geospiza scandens and Geospiza conirostris), the sharp-beaked ground finches (Geospiza difficilis) and the warbler finches (Certhidea olivacea and Certhidea fusca). Evidence of reduced genetic diversity due to drift was limited to warbler finches on small, peripheral islands. Evidence of low levels of recent interisland migration was widespread throughout all three groups. The hypothesis of distance-limited dispersal received the strongest support in cactus and sharp-beaked ground finches as evidenced by patterns of isolation by distance, while warbler finches showed a weaker relationship. Support for the hypothesis that gene flow constrains morphological divergence was only found in one of eight comparisons within these groups. Among warbler finches, genetic divergence was relatively high while phenotypic divergence was low, implicating stabilizing selection rather than constraint due to gene flow. We conclude that the adaptive radiation of Darwin's finches has occurred in the presence of ongoing but low levels of gene flow caused by distance-dependent interisland dispersal. Gene flow does not constrain phenotypic divergence, but may augment genetic variation and facilitate evolution due to natural selection. Both microsatellites and mtDNA agree in that subsets of peripheral populations of two older groups are genetically more similar to other species that underwent dramatic morphological change. The apparent decoupling of morphological and molecular evolution may be accounted for by a modification of Lack's two-stage model of speciation: relative ecological stasis in allopatry followed by secondary contact, ecological interactions and asymmetric phenotypic divergence.

Adaptation, Biological↗

PubMed1997

Effect of a chemical modification on the hydrated adenosine intermediate produced by adenosine deaminase and a model reaction for a potential mechanism of action of 5-aminoimidazole ribonucleotide carboxylase.

Using the hydrated adenosine intermediate (6R)-6-amino-1, 6-dihydro-6-hydroxy-9-(beta-D-ribofuranosyl)purine (2) produced by adenosine deaminase (ADA, EC 3.5.4.4) as a starting point, the active site probe and inhibitor platform 5-(formylamino)imidazole riboside (FAIRs, 4) was designed by removal of the-C6(OH)(NH2)-molecular fragment of 2 generated by the early events of the enzyme-catalyzed hydrolysis. FAIRs was synthesized directly from the sodium salt of 5-amino-1-(beta-D-ribofuranosyl)imidazole-4-carboxylic acid (CAIR) along a reaction sequence involving a tandem N-formylation/decarboxylation that may have a mechanistic connection to the Escherichia coli purE-catalyzed constitutional isomerization of N5-CAIR to CAIR. The physical and spectral properties of FAIRs were elucidated, its X-ray crystal and NMR solution structures were determined, and its interaction with ADA was investigated. Crystalline FAIRs exists solely as the Z-formamide rotamer and exhibits many of the same intramolecular hydrogen bonding events known to contribute to the association of Ado to ADA. In water and various organic solvents, however, FAIRs exists as NMR-distinct, slowly interconverting Z and E rotamers. This truncated enzymatic tetrahedral intermediate analog was determined to be a competitive inhibitor of ADA with an apparent Ki binding constant of 40 microM, a value quite close to that (33 microM) of the natural substrate's K(m). The actual species selected for binding by ADA, though, is likely the minor hydroxyimino prototropic form of Z-FAIRs possessing a far lower true Ki value. As the structural features of FAIRs appear well-suited to support its use as a template for constructing active site probes of both ADA and AIR carboxylases, a variety of carbohydrate-protected versions of FAIRs suitable for facile aglycon elaborations were synthesized. The N3-alkylation, N3-borane complexation, and C4-iodination of some of these were investigated in order to assess physicochemical properties that may assist in the elucidation of mechanisms for the AIR carboxylases. The survey of these properties taken together with a reasonable mechanism for the model CAIRs-->FAIRs synthetic transformation is interpreted to support a mechanism for the purE-catalyzed N5-CAIR-->CAIR biosynthetic one that involves a carboxylative sp3-rehybridization of the imidazole C4 atom rather than one possessing a dipole-stabilized C4 sp2 carbanionic intermediate.

Adenosine↗

PubMed2002

Exploring the stereochemistry of CXCR4-peptide recognition and inhibiting HIV-1 entry with D-peptides derived from chemokines.

Chemokine receptor CXCR4 plays an important role in the immune system and the cellular entry of human immunodeficiency virus type 1 (HIV-1). To probe the stereospecificity of the CXCR4-ligand interface, d-amino acid peptides derived from natural chemokines, viral macrophage inflammatory protein II (vMIP-II) and stromal cell-derived factor-1alpha (SDF-1alpha), were synthesized and found to compete with (125)I-SDF-1alpha and monoclonal antibody 12G5 binding to CXCR4 with potency and selectivity comparable with or higher than their l-peptide counterparts. This was surprising because of the profoundly different side chain topologies between d- and l-enantiomers, which circular dichroism spectroscopy showed adopt mirror image conformations. Further direct binding experiments using d-peptide labeled with fluorescein (designated as FAM-DV1) demonstrated that d- and l-peptides shared similar or at least overlapping binding site(s) on the CXCR4 receptor. Structure-activity analyses of related peptide analogs of mixed chiralities or containing alanine replacements revealed specific residues at the N-terminal half of the peptides as key binding determinants. Acting as CXCR4 antagonists and with much higher biological stability than l-counterparts, the d-peptides showed significant activity in inhibiting the replication of CXCR4-dependent HIV-1 strains. These results show the remarkable stereochemical flexibility of the CXCR4-peptide interface. Further studies to understand the mechanism of this unusual feature of the CXCR4 binding surface might aid the development of novel CXCR4-binding molecules like the d-peptides that have high affinity and stability.

Alanine↗

PubMed2006

Cervical dural arteriovenous fistula presenting with brainstem dysfunction: case report and review.

STUDY DESIGN: We present a rare case of cervical dural arteriovenous fistula (C-DAVF) presenting with brainstem dysfunction. We discuss the details of the case and review previous articles on C-DAVF. OBJECTIVES: Our case study illustrates the relation between uncommon neurologic findings and altered hemodynamics resulting from the anatomic features of the neural pathway. Based on a review of 31 cases of C-DAVFs published since 1990 (30 patients, including our own), we sought to determine which surgical treatment for C-DAVF, endovascular surgery, or direct interruption of the draining vein, is more effective. SUMMARY OF THE BACKGROUND DATA: A combination of endovascular techniques and direct interruption procedures was successful in curing the C-DAVF in our patient. The selection between endovascular surgery and surgical interruption in the treatment of C-DAVF is controversial. METHODS: We sought to identify the characteristics and surgical methods most closely associated with complete cure for C-DAVF. RESULTS.: According to the reports on 31 cases of C-DAVF treated surgically (including our own), 20 DAVFs were managed by open surgery with interruption, 8 were treated by endovascular surgery, and 3 underwent a combined open and endovascular approach. Twenty-one patients showed symptomatic improvement or stabilization without additional treatment during the postsurgical course. Surgical revisions were performed in 3 patients (10.0%) (including the present case), all of whom initially underwent endovascular surgery. None of the cases treated by surgical interruption of the draining vein showed signs of recurrence. CONCLUSIONS: Surgical interruption of the draining vein is more effective than endovascular surgery in bringing about an absolute cure for C-DAVF. In exceptional cases, however, endovascular surgery is the preferred treatment. This is particularly so for elderly or medically compromised cases with contraindications against general anesthesia, as well as for moribund cases which, like our own case, present with rapidly deteriorating neurologic status on admission.

Aged↗

PubMed1988

Plasma serine proteinase inhibitors (serpins) exhibit major conformational changes and a large increase in conformational stability upon cleavage at their reactive sites.

Intact and proteolytically modified human serpins, alpha 1-proteinase inhibitor, antithrombin III, alpha 1-antichymotrypsin, and C1 inhibitor, were compared by circular dichroism, fluorescence spectroscopy, and resistance against unfolding by guanidine HCl. The modified proteins were prepared from the intact and active inhibitors by selective proteolytic cleavage in their reactive site loops and tested for complete loss of activity. Significant differences in the spectral properties between intact and modified inhibitors indicate that a major conformational rearrangement is triggered by the cleavage. This leads to a large increase in conformational stability as demonstrated by large shifts of the transition profiles recorded as a function of guanidine HCl concentration at 20 degrees C by circular dichroism at 220 nm. Intact inhibitors were unfolded in two steps of about equal size centered at 0.8-1.7 and 2.5-3.5 M concentrations of the denaturant, respectively. Under identical conditions modified inhibitors are completely stable, and their denaturation occurs only well above 4 M guanidine HCl in one or two steep transition steps. From the similarity of the spectral changes and shifts in transition profiles for all four serpins studied it is concluded that the conformational changes and stabilization triggered by the modification hit is an important common mechanistic feature of this class of inhibitors. This is supported by the observation that ovalbumin, which is homologous with the serpins but apparently lacks inhibitory activity, exhibits neither spectral changes nor a significant change in stability upon proteolytic modification.

Algorithms↗

PubMed1987

[Effect of brain death on hemodynamics and cardiac function: an experimental study].

An experimental model was designed to study hemodynamic and left ventricular functional changes in the course of and after brain death in 13 mongrel dogs. Brain death was induced by creating intracranial hypertension by inflating a balloon inserted into the subdural space. Hemodynamic parameters and left ventricular systolic function as assessed by echocardiography were measured before and during intracranial hypertension and 30 min and 1, 2, 3, 5 and 8 hrs after brain death. During intracranial hypertension, heart rate, systemic and pulmonary blood pressures, cardiac output and systemic vascular resistance raised significantly. After brain death, all parameters decreased rapidly and significantly, and then stabilized. On comparison with values obtained before intracranial hypertension, systemic blood pressure decreased markedly following brain death, while no marked change was noted in cardiac output. This result is attributable to a marked reduction in peripheral vascular resistance following the induction of intracranial hypertension. The left ventricular end-diastolic and end-systolic diameters did not change; consequently, fractional shortening did not change, either. The Weissler's index improved after brain death, reflecting a marked reduction in systemic vascular resistance. This indicates limited usefulness of afterload-dependent cardiac indices. At the agonal period of brain death, three of 13 dogs died because of ventricular fibrillation or a marked decline in systemic blood pressure. Within five to eight hours after brain death, seven dogs died because of intractable acidosis. These results represent the specific hemodynamic features occurring after brain death. It is thought that recognition of these features is useful in managing cases of brain death and in selecting donors for heart transplants.

Animals↗

PubMedDate not supplied

Formation of an RNase A derivative containing an aminosuccinyl residue in place of asparagine 67.

At acidic pH, Asp67 and beta-Asp67 (beta-Asp: isoaspartic acid residue) derivatives of RNase A, obtained by selective deamidation of the parent enzyme, spontaneously produces a new derivative containing an aminosuccinyl residue (Asu). The overall secondary structure of the protein chain does not change as a consequence of this substitution, while the catalytic activity on RNA is reduced to about 25%. The pH dependence of the first-order rate constants for the Asu formation has a bell-shaped profile, the maximum being close to the pK(a) of the aspartic acid side chains. Moreover, the values of the rate constants are of the same magnitude of those measured for Asp-containing peptides whose sequence mimics the Asu formation site of the enzyme. This feature indicates that Asp67 and beta-Asp67 residues in the deamidated RNase A derivatives are sited in a region flexible enough to permit the cyclization of the carboxylic side chain to succinimide ring. These results are discussed at the light on to the three-dimensional structure and the thermodynamic stability of the aspartic acid derivatives of RNase A.

Amino Acid Sequence↗

PubMed1987

Lectin-specific targeting of lysosomal enzymes to reticuloendothelial cells.

The principles and methods used for enzymatic modification of the carbohydrate portion of glucocerebrosidase are similar to those performed by Ashwell and Morell, Stahl, and others. It is difficult to explain the lack of uptake of native enzyme through binding of the high-mannose type glycopeptide to Man/GlcNAc receptors since approximately 20% of the total oligosaccharides on the native enzyme are high mannose type. Possibly a requirement for multiple sites of attachment to the receptor is not met by a single high-mannose type oligosaccharide per molecule. Alternatively, the presence of complex type oligosaccharides on this enzyme, demonstrated by structural studies, may mask the mannose site and thus account for the poor uptake of native enzyme. The ability to successfully deglycosylate any protein or enzyme in order to specifically target a selected cell type requires that there be (1) an available source of pure enzyme; (2) specific exoglycosidases of high specific activity available either commercially or relatively easily purified; (3) chemical or biochemical means available for the testing of the product, preferably at each step; and (4) a means of separating the glycosidases used from the desired enzyme product. The characteristic and unique accumulation of glucocerebroside only in cells of the monocyte- histiocyte series, makes Gaucher's disease an excellent prototype for the study of enzyme replacement therapy. The principles demonstrated for the enzymatic deglycosylation of glucocerebrosidase may be applied to the cell-specific delivery of other glycoproteins as well. Other lysosomal diseases in which storage occurs in multiple cell types may be ameliorated by administration of macrophage-directed enzymes if, by so doing, storage material can be digested during the normal phagocytic turnover of senescent cells. Consideration of the kinetics of degradation and the structural features affecting the stability of enzymes in vivo are prerequisites to improving the bioengineering of targeted lysosomal enzymes. Animal and culture models have been developed for the study of glucocerebrosidase delivery to specific cell types and substrate degradation. Other studies have progressed toward a definition not only of the receptors at the plasma membrane involved in the internalization of exogenous enzyme, but also of internal receptors or properties of the lysosome responsible for intracellular protein trafficking. A complete understanding of the forces acting to direct endogenous or exogenously supplied enzyme to a given subcellular organelle will require a synthesis of experimental results from all areas of glycoprotein research.

Animals↗

PubMed1997

Junk DNA and sectorial gene repression.

Transcriptional repression in eukaryotes often involves tens or hundreds of kilobase pairs, two to three orders of magnitude more than the bacterial operator/repressor model does. Classical repression, represented by this model, was maintained over the whole span of evolution under different guises, and consists of repressor factors interacting primarily with promoters and, in later evolution, also with enhancers. The use of much larger amounts of DNA in the other mode of repression, here called the sectorial mode ('superrepression'), results in the conceptual transfer of so-called junk DNA to the domain of functional DNA. This contribution to the solution of the c-value paradox involves perhaps 15% of genomic 'junk,' and encompasses the bulk of the introns, thought to fill a stabilizing role in sectorially repressed chromatin structures. In the case of developmental genes, such structures appear to be heterochromatoid in character. However, solid clues regarding general structural features of superrepressed terminal differentiation genes remain elusive. The competition among superrepressible DNA sectors for sectorially binding factors offers, in principle, a molecular mechanism for developmental switches. Position effect variegation may be considered an abnormal manifestation of normal processes that underly development and involve heterochromatoid sectorial repression, which is apparently required for local elimination or modulation of morphological features (morpholysis). Sectorial repression of genes participating either in development or in terminal differentiation is considered instrumental in establishing stable cell types, and provides a basis for the distinction between determination and cell type specification. The gamut of possible stable cell types may have been broadened by the appearance in evolution of heavy isochores. Additional types of relatively frequent GC-rich cis-acting DNA motifs may offer reiterated binding sites to factors endowed with a selective (though not individually strong) affinity for these motifs. The majority of sequence motifs thought to be used in superrepression need not be individually maintained by natural selection. It is re-emphasized that the dispensability of sequences is not an indicator of their nonfunctionality and that in many cases, along noncoding sequences, nucleotides tend to fill functions collectively, rather than individually.

Animals↗

PubMed2005

Bis(mu-oxo)dicopper(III) complexes of a homologous series of simple peralkylated 1,2-diamines: steric modulation of structure, stability, and reactivity.

We have synthesized and characterized bis(mu-oxo)dicopper(III) dimers 1b-4b (Os) based on a core family of peralkylated trans-(1R,2R)-cyclohexanediamine (CD) ligands, self-assembled from the corresponding [LCu(MeCN)]CF3SO3 species 1a-4a and O2 at 193 K in aprotic media; additional Os based on peralkylated ethylenediamine and tridentate polyazacyclononane ligands were synthesized analogously for comparative purposes (5b-7b and 8b-9b, respectively). Trigonal-planar [LCu(MeCN)]1+ species are proposed as the active O precursors. The 3-coordinate Cu(I) complexes [(L(TE))Cu(MeCN)]CF3SO3 (4a) and [(L(TB))Cu(MeCN)]CF3SO3 (10a) were structurally characterized; the apparent O2-inertness of 10a correlates with the steric demands of its four benzyl substituents. The rate of O formation, a multistep process that likely proceeds via associative formation of a 1:1 [LCu(O2)]1+ intermediate, exhibits significant dependence upon ligand sterics and solvent: oxygenation of 4a-the slowest-reacting O precursor of the CD series-is first-order with respect to [4a] and proceeds at least 300 times faster in tetrahydrofuran than in CH2Cl2. The EPR, UV-vis, and resonance Raman spectra of 1b-9b are all characteristic of the diamagnetic bis(mu-oxo)dicopper(III) core. The intense ligand-to-metal charge transfer absorption maxima of CD-based Os are red-shifted proportionally with increasing peripheral ligand bulk, an effect ascribed to a slight distortion of the [Cu2O2] rhomb. The well-ordered crystal structure of [(L(ME))2Cu2(mu-O)2](CF3SO3)2.4CH2Cl2 ([3b. 4CH2Cl2]) features the most metrically compact [Cu2O2]2+ core among structurally characterized Os (av Cu-O 1.802(7) A; Cu...Cu 2.744(1) A) and exemplifies the minimal square-planar ligation environment necessary for stabilization of Cu(III). The reported Os are mild oxidants with moderate reactivity toward coordinating substrates, readily oxidizing thiols, certain activated alkoxides, and electron-rich phenols in a net 2e-, 2H+ process. In the absence of substrates, 1b-9b undergo thermally induced autolysis with concomitant degradation of the polyamine ligands. Ligand product distribution and primary kinetic isotope effects (kobsH/kobsD approximately 8, 1b/d24-1b, 293 K) support a unimolecular mechanism involving rate-determining C-H bond cleavage at accessible ligand N-alkyl substituents. Decomposition half-lives span almost 3 orders of magnitude at 293 K, ranging from approximately 2 s for 4b to almost 30 min for d(24)-1b, the most thermally robust dicationic O yet reported. Dealkylation is highly selective where ligand rigidity constrains accessibility; in 3b, the ethyl groups are attacked preferentially. The observed relative thermal stabilities and dealkylation selectivities of 1b-9b are correlated with NC(alpha)-H bond dissociation energies, statistical factors, ligand backbone rigidity, and ligand denticity/axial donor strength. Among the peralkylated amines surveyed, bidentate ligands with oxidatively robust NC(alpha)-H bonds provide optimal stabilization for Os. Fortuitously, the least sterically demanding N-alkyl substituent (methyl) gives rise to the most thermally stable and most physically accessible O core, retaining the potential for exogenous substrate reactivity.

Alkylation↗

PubMed2001

Identification of structural features in the G-protein regulatory motif required for regulation of heterotrimeric G-proteins.

The G-protein regulatory (GPR) motif, a conserved 25-30 amino acid domain found in multiple mammalian proteins, stabilizes the GDP-bound conformation of Galpha(i), inhibits guanosine 5'-O-(3-thiotriphosphate) (GTPgammaS) binding to Galpha(i) and competes for Gbetagamma binding to Galpha. To define the core GPR motif and key amino acid residues within a GPR peptide (TMGEEDFFDLLAKSQSKRMDDQRVDLAG), we determined the effect of truncation, insertion, and alanine substitutions on peptide-mediated inhibition of GTPgammaS binding to purified Galpha(i1). The bioactive core GPR peptide consists of 17 amino acids ((7)F-R(23)). Within this core motif, two hydrophobic sectors ((7)FF(8) and (10)LL(11)) and Q(22) are required for bioactivity, whereas M19A and R23A increased IC(50) values by 70-fold. Disruption of spatial relationships between the required sectors in the amino and carboxyl regions of the peptide also resulted in a loss of biological activity. Mutation of three charged sectors ((4)EED(6), R(18), (20)DD(21)) within the 28-amino acid GPR decreased peptide affinity by approximately 10-fold. Alanine substitutions of selected residues within the core GPR peptide differently influenced peptide inhibition of GTPgammaS binding to Galpha(i) versus Galpha(o). These data provide a platform for the development of novel, G-protein-selective therapeutics that inhibit Galpha(i)- mediated signaling, selectively activate Gbetagamma-sensitive effectors, and/or disrupt specific regulatory input to G-proteins mediated by GPR-containing proteins.

Alanine↗

PubMed1987

Microtubules containing acetylated alpha-tubulin in mammalian cells in culture.

The subcellular distribution of microtubules containing acetylated alpha-tubulin in mammalian cells in culture was analyzed with 6-11B-1, a monoclonal antibody specific for acetylated alpha-tubulin. Cultures of 3T3, HeLa, and PtK2 cells were grown on coverslips and observed by immunofluorescence microscopy after double-staining by 6-11B-1 and B-5-1-2, a monoclonal antibody specific for all alpha-tubulins. The antibody 6-11B-1 binds to primary cilia, centrioles, mitotic spindles, midbodies, and to subsets of cytoplasmic microtubules in 3T3 and HeLa cells, but not in PtK2 cells. These observations confirm that the acetylation of alpha-tubulin is a modification occurring in different microtubule structures and in a variety of eukaryotic cells. Some features of the acetylation of cytoplasmic microtubules of mammalian cells are also described here. First, acetylated alpha-tubulin is present in microtubules that, under depolymerizing conditions, are more stable than the majority of cytoplasmic microtubules. In addition to the specific microtubule frameworks already mentioned, cytoplasmic microtubules resistant to nocodazole or colchicine, but not cold-resistant microtubules, contain more acetylated alpha-tubulin than the rest of cellular microtubules. Second, the alpha-tubulin in all cytoplasmic microtubules of 3T3 and HeLa cells becomes acetylated in the presence of taxol, a drug that stabilizes microtubules. Third, acetylation and deacetylation of cytoplasmic microtubules are reversible in cells released from exposure to 0 degrees C or antimitotic drugs. Fourth, the epitope recognized by the antibody 6-11B-1 is not absolutely necessary for cell growth and division. This epitope is absent in PtK2 cells. The acetylation of alpha-tubulin could regulate the presence of microtubules in specific intracellular spaces by selective stabilization.

Acetylation↗

PubMed1996

Selective neural cell adhesion molecule signaling by Src family tyrosine kinases and tyrosine phosphatases.

Nerve growth cone guidance is a highly complex feat, involving coordination of cell adhesion molecules, trophic factor gradients, and extracellular matrix proteins. While navigating through the developing nervous system, the growth cone must integrate diverse environmental signals into a singular response. The repertoire of growth cone responses to these extracellular cues includes axonal growth, fasciculation, and synaptic stabilization, which are achieved through dynamic changes in the cytoskeleton and modulation of gene expression. It has become evident that interactions between cell adhesion molecules can activate intracellular signaling pathways in neurons. Such signaling pathways are just beginning to be defined for the axonal growth promoting molecules L1 and NCAM which are members of the immunoglobulin (Ig) superfamily. Recent findings have revealed that L1 and NCAM induce neurite outgrowth by activating intracellular signaling pathways in the growth cone mediated by two different members of the src family of nonreceptor protein tyrosine kinases (PTKs), pp60(c-src) and p59(fyn5,6). Growth cones display diverse morphologies and variable motility on these different cell adhesion molecules, which are likely to be generated by src kinases. In this review we will address novel features of nonreceptor PTKs of the src family which dictate their distinctive molecular interactions with cell adhesion molecules and signaling components.

Animals↗

PubMed1990

Physical characterization of the purified CCAAT transcription factor, alpha-CP1.

We have used DNA sequence affinity chromatography previously to purify a murine erythroid cell nuclear factor termed alpha-CP1. This promoter selective transcription factor is a heterotypic CCAAT factor composed of at least seven polypeptides with Mr values that range from 27,000 to 38,000. Peptide mapping experiments reported here show that these seven polypeptides fall into three distinct classes (alpha, beta, and gamma). In addition chemical cross-linking, sedimentation, and gel filtration studies suggest that alpha-CP1 is a heterotrimeric factor composed of one polypeptide from each class. A core component of the factor (alpha beta) is stable at moderately high ionic strengths, whereas the gamma polypeptides are more weakly associated with the particle. The native factor binds tightly to the alpha-globin CCAAT box (Kd = 5.71 x 10(-11 M), and mutational studies show that the DNA recognition site resides in a sequence decamer. DNA binding is significantly stabilized, however, by apparently nonspecific sequences 3' of the CCAAT recognition motif. Finally, the DNA binding domain of purified alpha-CP1 is moderately stable to protease digestion, a feature characteristic of heterotypic CCAAT factors. The proteolyzed factor has a slightly higher affinity for the CCAAT box (Kd = 2.8 x 10(-11) M), and its footprint cannot be distinguished from that of the intact factor. In contrast protease treatment abolishes the ability of alpha-CP1 to activate alpha-globin gene transcription in vitro. These latter results show that the DNA binding domain of alpha-CP1 is readily distinguished from the domains required to mediate activation of gene transcription.

Animals↗

PubMed2004

Evolutionary stability of mutualism: interspecific population regulation as an evolutionarily stable strategy.

Interspecific mutualisms are often vulnerable to instability because low benefit : cost ratios can rapidly lead to extinction or to the conversion of mutualism to parasite-host or predator-prey interactions. We hypothesize that the evolutionary stability of mutualism can depend on how benefits and costs to one mutualist vary with the population density of its partner, and that stability can be maintained if a mutualist can influence demographic rates and regulate the population density of its partner. We test this hypothesis in a model of mutualism with key features of senita cactus (Pachycereus schottii)-senita moth (Upiga virescens) interactions, in which benefits of pollination and costs of larval seed consumption to plant fitness depend on pollinator density. We show that plants can maximize their fitness by allocating resources to the production of excess flowers at the expense of fruit. Fruit abortion resulting from excess flower production reduces pre-adult survival of the pollinating seed-consumer, and maintains its density beneath a threshold that would destabilize the mutualism. Such a strategy of excess flower production and fruit abortion is convergent and evolutionarily stable against invasion by cheater plants that produce few flowers and abort few to no fruit. This novel mechanism of achieving evolutionarily stable mutualism, namely interspecific population regulation, is qualitatively different from other mechanisms invoking partner choice or selective rewards, and may be a general process that helps to preserve mutualistic interactions in nature.

Animals↗

PubMedDate not supplied

[Is portacaval anastomosis still valid treatment for portal hypertension in alcoholic cirrhotic patients?].

Mortality and quality of survival after portacaval anastomosis in cirrhotic patients are such that the validity of the operation was investigated during a retrospective study of 242 cases, operation being for hemorrhage and involving emergency or delayed surgery. Operative mortality was higher in emergency cases, but was improved by stricter selection criteria, particularly of pathological features. Cause of death from secondary factors varied during the two years following anastomosis, with perhaps a high frequency of hepatic failure. Recurrence of hemorrhage was a serious complication often related to hepatic insufficiency, while the onset of combined jaundice-edema-ascites (1 out of 4 patients) was frequently the result of continued alcohol abuse. Portacaval encephalopathy (24,4%) did not worsen the vital prognosis, and was severe in only 3 cases. Alcohol intoxication was very frequent in minor forms. Edema of the lower limbs (34,4% of cases), a frequent complication, appeared to result mainly from hemodynamic causes. A return to work was not possible in 20% of patients, but in only 12% was this due to the anastomosis. Portacaval anastomosis would not, therefore, appear to alter survival of patients from complications of cirrhosis. It suppresses the hemorrhagic risk, however, and the course of the disease is then related only to the cirrhosis and to its stability if abstinence is maintained.

Adult↗