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PubMed1979

Integral membrane protein interaction with Triton cytoskeletons of erythrocytes.

The organization of erythrocyte membrane lipids and proteins has been studied following the release of cytoplasmic components with the non-ionic detergent Triton X-100. After detergent extraction, a detergent-resistant complex called the erythrocyte cytoskeleton is separated from detergent, solubilized lipid and protein by sucrose buoyant density sedimentation. In cytoskeletons prepared under isotonic conditions all of the major erythrocyte membrane proteins are retained except for the integral protein, glycophorin, which is quantitatively solubilized and another integral glycoprotein, band 3, which is only 60% removed. When cytoskeletons are prepared in hypertonic KCl solutions, band 3 is fully solubilized along with bands 2.1 and 4.2 and several minor components. The resulting cytoskeletons have the same morphology as those prepared in isotonic buffer but they are composed of only three major peripheral proteins, spectrin, actin and band 4.1. We have designated this peripheral protein complex the 'shell' of the erythrocyte membrane, and have shown that the attachment of band 3 to the shell satisfies the criteria for a specific interaction. Although Triton did affect erythrocyte shape, cytoskeleton lipid content and the activity of membrane proteases, there was no indication that Triton altered the attachment of band 3 to the shell. We suggest that band 3 attaches to the shell as part of a ternary complex of bands 2.1, 3 and 4.2.

Erythrocyte Membrane↗
PubMed1988

Interaction of amphiphiles with integral membrane proteins. II. A simple, minimal model for the nonspecific interaction of amphiphiles with the anion exchanger of the erythrocyte membrane.

In a previous paper we have reported on the structural perturbation of the erythrocyte membrane anion exchanger by a regular series of model amphiphiles, as shown by differential scanning calorimetry (Gruber, H.J. and Low, P.S., Biochim. Biophys. Acta, preceding article). Now the data are interpreted by a model in which the effects of amphiphile structure upon buffer-membrane partitioning are well separated from the dependence of the intrinsic potencies of membrane-bound amphiphiles upon amphiphile structure. The buffer-membrane partitioning situation was demonstrated to regularly change between extremes within a series of homologous amphiphiles, i.e. from a negligible to a predominant fraction of total amphiphile in the sample residing in the membrane. Based upon this demonstration a large number of reports on the chain length dependence of apparent potency could be reinterpreted in terms of chain length profiles of intrinsic potency, allowing for a comparison of the responses of various membrane proteins to homologous series of amphiphiles. The response patterns for chain length variation could be divided into three distinct classes: the intrinsic potency (i) can be independent of chain length over a very wide range of length, (ii) it can be rather independent up to a critical length where a sudden cut-off in potency occurs, or (iii) it can drop monotonically over a wide range of chain length. The intrinsic potency values of saturated fatty acids in destabilizing the anion exchanger were interpreted by very simple assumptions: only direct interactions between amphiphiles and target proteins and a simple amphiphile partition equilibrium between a pool of equivalent low affinity sites on the protein and the bulk lipid matrix. The observed monotonic decay of the intrinsic potency of saturated fatty acids with increasing chain length from C8 to C20 was translated into a constant increment of free energy by which each additional CH2 favors the transfer away from sites on the protein towards the bulk lipid matrix. Arguments were presented suggesting that the direct interaction between amphiphiles and target protein is completely nonspecific for alkyl chain length while the residual specificity for shorter over longer amphiphiles is due to the higher tendency of longer chains to preferentially bind in the bulk lipid matrix. Thus a completely new role of the lipid as a competitor, rather than a mediator, was postulated.

Cell Membrane↗
PubMed1996

Interaction between an integral protein of the nuclear envelope inner membrane and human chromodomain proteins homologous to Drosophila HP1.

At the nuclear envelope in higher eukaryotic cells, the nuclear lamina and the heterochromatin are adjacent to the inner nuclear membrane, and their attachment is presumably mediated by integral membrane proteins. In a yeast two-hybrid screen, the nucleoplasmic domain of lamin B receptor (LBR), an integral protein of the inner nuclear membrane, associated with two human polypeptides homologous to Drosophila HP1, a heterochromatin protein involved in position-effect variegation. LBR fusion proteins bound to HP1 proteins synthesized by in vitro translation and present in cell lysates. Antibodies against LBR also co-immunoprecipitated HP1 proteins from cell extracts. LBR can interact with chromodomain proteins that are highly conserved in eukaryotic species and may function in the attachment of heterochromatin to the inner nuclear membrane in cells.

Amino Acid Sequence↗
PubMed1982

Role of membrane integrity and cation interaction for heart sarcolemmal adenylate cyclase and Na+-K+ ATPase.

The adenylate cyclase and Na+ -K+ ATPase activities decreased on storage at 4 degrees C as well as on freezing and thawing of the rat heart sarcolemma. Treatment of the sarcolemmal fraction with phospholipase C and trypsin also depressed the adenylate cyclase and Na+ -K+ ATPase activities; the Na+ -K+ ATPase was more sensitive to these treatments than the adenylate cyclase. When the sarcolemmal enzyme activities were determined in the presence of different concentrations of some cations the adenylate cyclase activity was enhanced and the Na+ -K+ ATPase activity was depressed by monovalent cations (Na+, K+, Rb+, Cs+, Li+, and NH+4). Divalent cations such as Sr2+, Ba2+, Co2+, and Mn2+ had biphasic or no effects on the adenylate cyclase activity but inhibited the Na+ -K+ ATPase activity. Although Ca2+, Ni2+, Cd2+, Cu2+, Hg2+, and Zn2+ depressed both Na+ -K+ ATPase and adenylate cyclase activities, the degree of inhibition of these enzymes was different. These results reveal the role of membrane integrity for full expression of the adenylate cyclase and Na+ -K+ ATPase activities, whereas both monovalent and divalent cations appear to regulate sarcolemma-bound enzyme activities.

Adenylyl Cyclases↗
PubMed1990

Alterations in the p'R promoter of coliphage lambda modify both its activity and interaction with the integration host factor (IHF).

A limited number of deletion/insertions and a point mutation in the -35 region of the p'R promoter of phage lambda were examined and found to influence both transcription and its repression by the integration host factor (IHF). Positive effects on transcription (in the absence of IHF) are small (up to 1.4-fold) and are caused by a deletion-substitution upstream of the -35/ihf site. Up to three base changes in the -35 promoter element seem to be tolerated, with only a small negative effect on transcription. In some cases, effective transcription requires supercoiling of such mutant template. Since an ihf sequence overlaps the -35 region of p'R, IHF represses transcription. Repression is correlated with IHF binding and consequent DNA bending, as assessed by gel retardation experiments. Nine p'R mutants were tested for their IHF binding and repression; the results confirm the consensus sequence, 5'-W2WWWWN7WWWWCARNWN2TTR derived from the hydroxyl radical footprinting, where the bold letters indicate the IHF-protected bases and W is A or T, R is A or G and N represents A, T, G or C. Perhaps surprisingly, some mutations just upstream or downstream of this ihf sequence also affect IHF binding, as observed not only for the pR'/ihf but also for the att H' site of lambda. Supercoiling in some cases permits the IHF-mediated repression to be overcome, probably by increasing the RNA polymerase binding and/or decreasing the interaction with IHF. All our data are consistent with a model which assumes that IHF initially binds to one or two ihf contact points depending on preexisting DNA topology, bends DNA, and completes the remaining contacts while finally adjusting the DNA conformation to establish the best fit within the minor groove of the double helix. Effective IHF repression of transcription would thus depend on several factors, including: (1) the sequence, and (2) the initial conformation of the ihf site, together with (3) the capacity of IHF to compete with RNA polymerase for the overlapping binding sites.

Bacterial Proteins↗
PubMed1990

Effects of contextual integration on recall of pictures by older adults.

This study investigated age-related differences in the ability to utilize integrative relationships between target and context as a memory support by directly manipulating the relationship between a target picture and context. We hypothesized that as the active integration required between target and cue increased, age differences would increase. Old and young adults were instructed to remember target pictures, each presented with a pictorial cue. The cue/target relationship was one of three types: categorically related (high integration condition), visually interacting (high integration condition), or unrelated and noninteracting (low integration condition). Cued recall of the targets was tested. The results indicated that the poorly integrated target-context relationship produced the largest age difference, supporting the integration hypothesis.

Adolescent↗
PubMed1990

Two requirements for job contentment: autonomy and social integration.

The interaction of autonomy (control over work activities) and social integration (relationships with co-workers) was investigated in a sample of newly employed nurses in the 6th and 12th month of work. Those nurses with low autonomy and low social integration reported low job satisfaction and work motivation, poor commitment to the organization and less intent to stay on the job. They were older, with more experience and more education and tended to work on medical units. This study supports the notion of feminist psychologists that what women nurses want is "autonomy with connectedness".

Adult↗
PubMed1988

The interaction of Escherichia coli integration host factor with the cohesive end sites of phages lambda and 21.

The interaction of E. coli integration host factor (IHF) with the cohesive end sites (cos's) of phages lambda and 21 has been studied by the DNAase I footprinting technique. Six potential sites in cos lambda differ from the consensus IHF binding sequence by 1 to 3 base pairs. Of the six, one site, I1, binds IHF strongly. The I1 segment protected by IHF contains two sequences that closely match the IHF consensus binding sequence. Another site, I2, binds IHF moderately well, and three sites: 10', 13 and 14 bind IHF very weakly. The 10 site does not bind IHF under the conditions used here. In phage 21 the DNA segment extending to the right from the cohesive ends, which contains three potential IHF binding sites, was examined. Two sites bind IHF well; I1, the 21 analogue of one of the lambda I1 sites, and I0, a site not analogous to a lambda site. The third 21 site, I2, binds IHF moderately well, as does the analogous I2 site in lambda. The significance of the results for lambda DNA packaging is discussed.

Bacterial Proteins↗
PubMed1989

The interaction of E. coli integration host factor and lambda cos DNA: multiple complex formation and protein-induced bending.

The interaction of E. coli's integration Host Factor (IHF) with fragments of lambda DNA containing the cos site has been studied by gel-mobility retardation and electron microscopy. The cos fragment used in the mobility assays is 398 bp and spans a region from 48,298 to 194 on the lambda chromosome. Several different complexes of IHF with this fragment can be distinguished by their differential mobility on polyacrylamide gels. Relative band intensities indicate that the formation of a complex between IHF and this DNA fragment has an equilibrium binding constant of the same magnitude as DNA fragments containing lambda's attP site. Gel-mobility retardation and electron microscopy have been employed to show that IHF sharply bends DNA near cos and to map the bending site. The protein-induced bend is near an intrinsic bend due to DNA sequence. The position of the bend suggests that IHF's role in lambda DNA packaging may be the enhancement of terminase binding/cos cutting by manipulating DNA structure.

Bacterial Proteins↗
PubMed1986

Interactive multi-window integration of two-parameter flow cytometric data fields.

Integration is necessary to determine the particle content of regions of interest of flow cytometric two-parameter fields. The improved program of the Cytomic 12 analyzer (1) offers: window trace integration for relatively simple window structures. The field of interest is surrounded by an integration trace (window). Eight independent windows can be stored and successively evaluated. It also offers painted field integration for complicated window structures. The pointer or a small window is interactively moved over the structures to be integrated like the brush of a painter. The "painted field" defines the window to be integrated. Window sets and painted fields can be stored on a floppy disk. Painted fields can be added and may also serve as look up tables for sorting.

Cell Count↗
PubMed1995

Mechanochemistry of protein 4.1's spectrin-actin-binding domain: ternary complex interactions, membrane binding, network integration, structural strengthening.

Mechanical strength of the red cell membrane is dependent on ternary interactions among the skeletal proteins, spectrin, actin, and protein 4.1. Protein 4.1's spectrin-actin-binding (SAB) domain is specified by an alternatively spliced exon encoding 21 amino acid (aa) and a constitutive exon encoding 59 aa. A series of truncated SAB peptides were engineered to define the sequences involved in spectrin-actin interactions, and also membrane strength. Analysis of in vitro supramolecular assemblies showed that gelation activity of SAB peptides correlates with their ability to recruit a critical amount of spectrin into the complex to cross-link actin filaments. Also, several SAB peptides appeared to exhibit a weak, cooperative actin-binding activity which mapped to the first 26 residues of the constitutive 59 aa. Fluorescence-imaged microdeformation was used to show SAB peptide integration into the elastic skeletal network of spectrin, actin, and protein 4.1. In situ membrane-binding and membrane-strengthening abilities of the SAB peptides correlated with their in vitro gelation activity. The findings imply that sites for strong spectrin binding include both the alternative 21-aa cassette and a conserved region near the middle of the 59 aa. However, it is shown that only weak SAB affinity is necessary for physiologically relevant action. Alternatively spliced exons can thus translate into strong modulation of specific protein interactions, economizing protein function in the cell without, in and of themselves, imparting unique function.

Actins↗
PubMed1986

Mutational analysis of integrase arm-type binding sites of bacteriophage lambda. Integration and excision involve distinct interactions of integrase with arm-type sites.

Integrative recombination between specific attachment (att) regions of the bacteriophage lambda genome (attP) and the Escherichia coli genome (attB) results in a prophage flanked by the hybrid recombinant sites attL and attR. Each att site contains sequences to which proteins involved in recombination bind. Using site-directed mutagenesis, we have constructed a related set of point mutations within each of the five Int "arm-type" binding sites located within attP, attL and attR. Footprint analyses of binding demonstrate that mutating the arm-type sites significantly disrupts the binding of Int. Recombination analyses of mutant att sites in vivo and in vitro demonstrate that only three wild-type arm-type sites within attP are required for efficient integrative recombination. Similar analyses demonstrate that efficient excision can occur with two other different sets of wild-type arm-type sites in attL and attR. These results demonstrate that integrative and excisive recombination may involve interactions of Int with distinct and different subsets of arm-type sites.

Attachment Sites, Microbiological↗
PubMed1993

Biologic and immunologic approaches to comprehensive therapy for pediatric malignant conditions. Laboratory-clinical interaction.

Cooperative integration of laboratory and clinical trial data has provided striking improvement in the treatment of pediatric malignant conditions over the last 2 decades. If attempts are made to individualize therapy to the specific disease and prognostic treatment subgroups for each pediatric malignant condition, the combination of surgery, radiation therapy, and chemotherapy can put the vast majority of patients into a complete clinical remission, with apparent cure for more than half of these patient. Depending on the disease type, treatment failure, when it occurs, is usually the result of recurrent, distant, metastatic disease that is refractory to prior treatment and simultaneously refractory to treatment approaches not yet used for the patient who has had a relapse. The clinical research challenge with these pediatric malignant neoplasms is to identify those children who are harboring microscopic amounts of residual tumor before their relapse and develop effective combined well-tolerated treatment approaches that can be initiated in those patients. These additional treatment approaches should complement rather than duplicate the biologic mechanisms that had been used to initiate remission to eradicate residual tumor without cross resistance. Ongoing laboratory and clinical research approaches are developing and testing the potential of biologic/immunologic therapeutics. The broad application of these principles to clinical oncology will be facilitated by the integrated laboratory-clinical testing that is being accomplished through cooperative pediatric clinical research trials.

Antibodies, Monoclonal↗
PubMed1985

The phi 80 and P22 attachment sites. Primary structure and interaction with Escherichia coli integration host factor.

Although the lambdoid bacteriophage phi 80 and P22 possess site-specific recombination systems analogous to bacteriophage lambda, they have different attachment (att) site specificities. We have identified and determined the nucleotide sequences of the att sites of phi 80 and P22 and have examined the interaction of these sites with purified Escherichia coli integration host factor (IHF). The sizes of the homologous core regions of the att sites vary greatly: P22 has a 46-base pair core, while phi 80 and lambda have 17- and 15-base pair cores, respectively. The core sequences of the three phage show no significant homology, although dispersed regions of homology in arm sequences indicate that the three phage att sites are related. All three att sites have a high A + T composition, and restriction fragments carrying these sites migrate anomalously upon polyacrylamide gel electrophoresis. IHF binds to a site to the left of the common core in the phi 80 and P22 phage att sites (attP) and to a site to the right of the core in P22 attP and attB (the bacterial att site). In the lambda system, IHF interacts with three regions on attP (designated H1, H2, and H') and none on attB (Craig N., and Nash, H.A. (1984) Cell 39, 707-716). Alignment of the IHF sites of all three phage results in a consensus sequence for IHF binding, Pyr-AANNNNTTGATAT. Among the three phage, the number of IHF sites differs; however, the location and orientation of the binding sites in relation to the respective core regions are well conserved. An IHF site analogous to lambda H2 is present in both phi 80 and P22 attP, while a site analogous to lambda H' is present in P22 attP. This conservation suggests that IHF plays a very similar role in the site-specific recombination pathways of all three phage, and that the flanking arm sequences are necessary for phi 80 and P22 attP function, as is the case for lambda attP function. These structural similarities presumably reflect a conservation of the mechanism of site-specific recombination for the three phage.

Bacteriophage lambda↗
PubMed1991

Use of monoacetyl-4-hydroxyaminoquinoline 1-oxide to probe contacts between guanines and protein in the minor and major grooves of DNA. Interaction of Escherichia coli integration host factor with its recognition site in the early promoter and transposition enhancer of bacteriophage Mu.

Monoacetyl-4-hydroxyaminoquinoline 1-oxide (Ac-HAQO) reacts with DNA to form adducts at the C8- and N2-positions of guanine and with the N6-position of adenine. Only the N2-guanine adduct blocks the 3'-5' exonuclease action of phage T4 DNA polymerase. Piperidine treatment cleaves the DNA at sites bearing C8-guanine adducts. The N2-position of guanine lies in the minor groove of DNA, whereas the C8-position of guanine occupies the major groove. We have taken advantage of these characteristics to employ Ac-HAQO in conjunction with either T4 DNA polymerase or piperidine in a footprinting technique to probe the interaction of the Escherichia coli integration host factor (IHF) with its binding site. We show that when IHF binds to its recognition site both the N2- and C8-positions of guanines are protected from modification by AcHAQO. In addition, the binding of IHF to DNA was prevented when either an N2- or a C8-AQO adduct was present in the binding site. When dimethylsulfate was used as the footprinting reagent, IHF protected against methylation of the N3 position of adenine in the minor groove but not the N7 position of guanine in the major groove. The difference in results obtained with the two reagents is ascribed to their relative sizes. Both DMS and AcHAQO are excluded by IHF from the minor groove, but only the larger AcHAQO molecule is excluded from the major groove.

Aminoquinolines↗