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PubMed1995

Structural features of a superfamily of zinc-endopeptidases: the metzincins.

A large number of zinc endopeptidases contain an HEXXHXXGXXH consensus motif in their catalytic site (single letter code; X is any amino acid residue). These enzymes can be grouped into four distinct families, the astacins, the adamalysins, the serralysins and the matrix metalloproteinases (matrixins). Despite a low degree of sequence similarity, their catalytic modules are topologically similar. A topology derived sequence alignment suggests that the four families form a superfamily, called the metzincins because of a perfectly superimposable methionine residue close to the zinc-binding active site. Topological similarity to the thermolysin-like enzymes indicates that these enzymes may have had a common ancestor.

Amino Acid Sequence↗
PubMed1991

Products of estradiol/peroxidase interaction; their structural features and biopolymeric character.

Loss of tritium from [2,4,6 alpha, 7 alpha-3H]estradiol and from [2-3H]estradiol during their conversion into polyestradiol (PEL) by horseradish peroxidase/H2O2 and the NMR spectrum of PEL permethyl ether suggest that PEL is composed of two or more different subunits, each formed by the joining of four molecules of estradiol with the loss of five hydrogen atoms from positions 2 and 4 and of three phenolic hydrogens leading to the formation of one C-C bond and three C-O bonds. At very low concentrations of estradiol the main reaction products were monomers; this is attributed to the initial formation of transient tetraestradiols which combine with water at high dilution and with themselves at low dilution. Association of the monomeric products to oligomers occurred on a Sephadex G-50 column and was readily reversed in phosphate buffer. In aqueous solution PEL underwent non-covalent changes induced by heat, time and electrolytes, and affecting its solubility, u.v. absorbance, extraction by organic solvents and ability to bind estradiol.

Biopolymers↗
PubMed2004

Structural features of the initiator of replication protein RepB encoded by the promiscuous plasmid pMV158.

The promiscuous rolling circle (RC)-replicating plasmid pMV158 encodes the 210-amino-acid initiator of replication protein, RepB. The protein relaxes supercoiled cognate DNA in a topoisomeraseI-like manner. A new vector and procedure for overproduction, scaling-up, and purification of the protein has been developed. RepB purified as a hexamer in solution, as shown by analytical ultracentrifugation assays. Circular dichroism (CD) of RepB indicated that the protein has an estimated content of around 33% alpha-helices and 20% beta-strands. Characterisation of temperature-induced transitions of the protein showed an irreversible change in the spectra when the temperature was raised above 35 degrees C, indicating that the protein undergoes a conformational change that could account for the relatively high optimal temperature of the RepB-mediated cleavage.

Amino Acid Sequence↗
PubMed2004

Structural features of pectic polysaccharides from the skin of Opuntia ficus-indica prickly pear fruits.

After removal of the mucilage with water at room temperature, pectic polysaccharides were solubilized from Opuntia ficus-indica fruit skin, by sequential extraction with water at 60 degrees C (WSP) and EDTA solution at 60 degrees C (CSP). Polysaccharides with neutral sugar content of 0.48 and 0.36 mol/mol galacturonic acid residue were obtained, respectively, in the WSP and CSP extracts. These pectic polysaccharides were de-esterified and fractionated by anion-exchange chromatography, yielding for each extract five fractions, which were thereafter purified by size-exclusion chromatography. Two of these purified fractions were characterized by sugar analysis combined with methylation and reduction-methylation analysis. The study was then supported by (1)H and (13)C NMR spectroscopy. The results showed that the water-soluble fraction WSP3 and the EDTA soluble fraction CSP3, consisted of a disaccharide repeating unit -->2)-alpha-l-Rhap-(1-->4)-alpha-d-GalpA-(1--> backbone, with side chains attached to O-4 of the rhamnosyl residues. The side chains contained highly branched alpha-(1-->5)-linked arabinan and short linear beta-(1-->4)-linked galactan.

Anions↗
PubMed2004

Pectin methylesterases: sequence-structural features and phylogenetic relationships.

Pectin methylesterases (PMEs) are enzymes produced by bacteria, fungi and higher plants. They belong to the carbohydrate esterase family CE-8. This study deals with comparison of 127 amino acid sequences of this family containing the five characteristic sequence segments: 44_GxYxE, 113_QAVAL, 135_QDTL, 157_DFIFG, 223_LGRPW (Daucus carota numbering). Six strictly conserved residues (Gly44, Gly154, Asp157, Gly161, Arg225 and Trp227) and six conservative ones (Ile39, Ser86, Ser137, Ile152, Ile159 and Leu223) were identified. A set of 70 representative PMEs was created. The sequences were aligned and the evolutionary tree based on the alignment was calculated. The tree reflected the taxonomy: the fungal and bacterial PMEs formed their own clusters and the plant enzymes were grouped into eight separate clades. The plant PME from Vitis riparia was placed in a common clade with fungi. Three plant clades (Plant 1, 2 and 3) were relatively homogenous reflecting high degree of mutual sequence identity. The clade Plant 4 contained PMEs from flower parts (mostly form pollen) and was heterogenous, like the clades Plant 1a and 2a, which moreover exhibit an intermediate character. The clades Plant X1 and X2 were situated in the tree close to microbial clades and represented atypical plant PMEs. Taking into account the remaining plant PMEs, an expanded plant alignment and tree (with most Arabidopsis thaliana and Oryza sativa enzymes), were prepared. An exclusive Arabidopsis alignment and tree indicated the existence of a new plant clade X3. In the pre pro region of most plant enzymes a longer conserved segment containing basic dipeptide, R(K)/R(K), that precedes the N-terminal end of PME was revealed. This was not observed in the clade Plant X1 and majority of the clade Plant X2. This study brings further the description of occurrence of potential glycosylation sites in pre pro sequences and in mature enzymes as well as important amino acid residues, such as aspartates, cysteines, histidines and other aromatic residues (Tyr, Phe and Trp), with discussion of their possible function in the activity of PMEs.

Amino Acid Sequence↗
PubMed2006

Analysis of structural features of deformed spines in frontal and sagittal projections.

In the study of spine, two approaches exist. Clinicians still measure directly, either on X-ray films or on digitized images, a small number of angular values characterizing the profile of deformed spines. 3D software programs exist, but they describe the spinal features calculated from a large set number of inputs. An alternative approach is proposed for clinical applications. Frontal and sagittal radiographs are treated separately. Neutral curves are drawn from a small number of records in a small amount of time. Feature parameters accurately describe the spinal shape, and they are the basis for drawing the modeled curve of the spine. These parameters facilitate the follow up of evolutive back pathologies. Several examples display the new technique.

France↗
PubMed2004

Structural features of hematopoiesis-specific RhoH/ARHH gene: high diversity of 5'-UTR in different hematopoietic lineages suggests a complex post-transcriptional regulation.

The hematopoiesis-specific RhoH gene is thought to be deregulated in B-cell non-Hodgkin's lymphoma (B-NHL), by either a chromosomal translocation or mutations, which affect its 5' regulatory region. The encoded Rho protein, always GTP-bound in vivo, was hypothesized to behave as a Rac antagonist. Extensive expression analysis allowed the detection of RhoH transcripts in all hematopoietic lineages (lymphoid, erythroid, myeloid), with a high level in lymphoid cells. To initiate investigations on the molecular mechanisms that regulate RhoH gene expression, Race-PCR and primer extension were conducted in the B-cell line Raji, which allowed (i) the establishment of RhoH complex intron/exon organization and (ii) the detection of several transcription initiation sites. In addition, a high 5' end heterogeneity of RhoH mRNAs was observed, due to alternative splicing of some 5' exons and to the use of these different transcription start sites. RT-PCR analysis led to the identification of this 5' end heterogeneity in different hematopoietic lineages. Discrepancies were particularly observed between B and T cells, due to an alternative splicing of one 5' exon (1b), which might be an important element in RhoH gene regulation. Such specific features have never been described for any Rho family member gene. They provide a molecular basis to study complex mechanisms involved in the control of RhoH expression.

5' Untranslated Regions↗
PubMed2004

Structural features and mechanisms for sensing high osmolarity in microorganisms.

During their lifetime, most organisms experience osmotic stress, mostly due to fluctuating external osmolarities, but also as a result of desiccation or freezing. Under these conditions, the ratio of osmolytes to water and macromolecules in the cells is significantly altered. To survive, cells must continuously sense these alterations and adapt accordingly. Osmolarity is a physico-chemical parameter that causes pleiotropic alterations in cell physiology. Recent research has revealed various mechanisms to sense high external osmolarity, based on monitoring cellular changes that are associated with the altered environment.

Bacterial Physiological Phenomena↗
PubMed1988

Enzymatic sulfation of salivary mucins: structural features of 35S-labeled oligosaccharides.

Sulfotransferase activity catalyzing the transfer of sulfate ester group from 3'-phosphoadenosine-5'-phosphosulfate to salivary mucins was found associated with Golgi-rich membrane fraction of rat submandibular salivary glands. Alkaline borohydride reductive cleavage of the synthesized 35S-labeled glycoprotein led to the liberation of the label into reduced acidic oligosaccharides. Most of the label was found incorporated in four oligosaccharides. These were identified as sulfated tri-, penta-, hepta- and nonasaccharides. The trisaccharide was characterized as SO3H,6GlcNAc beta 1,3Gal beta 1,3GalNac-o1, the pentasaccharide as SO3H,6GlcNAc beta 1,3Gal beta 1,4GlcNAc beta 1,3(NeuAc alpha 2,6) GalNAc-o1 and heptasaccharide as SO3H,6Gal beta 1,4GlcNAc beta 1,6(Fuc alpha 1) 2Gal beta 1,4GlcNAc beta 1,3Gal beta 1,3)GalNAc-o1.

Animals↗
PubMed1998

Structural features that modulate the transmembrane migration of a hydrophobic peptide in lipid vesicles.

Two approaches employing nuclear magnetic resonance (NMR) were used to investigate the transmembrane migration rate of the C-terminal end of native alamethicin and a more hydrophobic analog called L1. Native alamethicin exhibits a very slow transmembrane migration rate when bound to phosphatidylcholine vesicles, which is no greater than 1 x 10(-4) min(-1). This rate is much slower than expected, based on the hydrophobic partition energies of the amino acid side chains and the backbone of the exposed C-terminal end of alamethicin. The alamethicin analog L1 exhibits crossing rates that are at least 1000 times faster than that of native alamethicin. A comparison of the equilibrium positions of these two peptides shows that L1 sits approximately 3-4 A deeper in the membrane than does native alamethicin (Barranger-Mathys and Cafiso. 1996. Biochemistry. 35:489). The slow rate of alamethicin crossing can be explained if the peptide helix is irregular at its C-terminus and hydrogen bonded to solvent or lipid. We postulate that L1 does not experience as large a barrier to transport because its C-terminus is already buried within the membrane interface. This difference is most easily explained by conformational differences between L1 and alamethicin rather than differences in hydrophobicity. The results obtained here demonstrate that side-chain hydrophobicity alone cannot account for the energy barriers to peptide and protein transport across membranes.

Alamethicin↗
PubMed1999

Structural features of single amino acid repeats in proteins.

Single amino acid repeats are found in different kinds of proteins. Some of these repeats are pathogenic. It is striking that some amino acids are able to form such repeats, but other amino acids are not. We suggest an explanation for this fact based on the different tendency of each amino acid to form aggregates. Aggregation may be due to the formation of incipient lamellar crystals as they have been described in poly-alpha-amino acids and in most synthetic polymers.

Amino Acids↗
PubMed1986

Interspecific nucleotide sequence comparisons used to identify regulatory and structural features of the Drosophila hsp82 gene.

We have sequenced the hsp82 heat shock gene and 5'-flanking DNA of four species of Drosophila in order to identify conserved features of possible regulatory significance and to determine the nature and rate of evolutionary change in various domains of the gene. All conserved sequences identified in the 5' non-transcribed region of the hsp82 gene of melanogaster, simulans, pseudoobscura and virilis lie within 150 base-pairs of the RNA initiation site. These include a 34 base-pair imperfect but highly conserved dyad made up of three overlapping copies of the consensus heat shock regulatory sequence dyad made up of three overlapping copies of the consensus heat shock regulatory sequence C-T-N-G-A-A-N-N-T-T-C-N-A-G. Several other highly conserved features are also seen. In pseudoobscura only, the region from -21 to -133 is almost exactly repeated 698 base-pairs upstream. The upstream repeat retains all of the sequences common to the four species in the -21 to -133 interval except for the T-A-T-A motif. One possibility is that this upstream sequence is involved in dosage compensation of the hsp82 gene, which is pseudoobscura is on the X chromosome. In melanogaster, simulans and virilis there is an oppositely oriented, non-heat shock gene 0.6 to 0.8 kb (kb = 10(3) base-pairs) upstream from the hsp82 transcription initiation site. Comparisons of the hsp82 transcription unit from the distantly related species show little or no sequence conservation in the intron and non-translated exon I sequences. In contrast, the coding regions of these species are 90% homologous at the DNA level and 97 to 99% identical at the amino acid level. Half of the amino acid changes have occurred within a 15-amino acid region that lies within an unusually polar domain of hsp82. From the sequence comparisons, we estimate the rate of silent (synonymous) site substitution in Drosophila as 1 X 10(-8)/nucleotide site per year, similar to that for mammals.

Amino Acid Sequence↗
PubMed1990

Structural features of a regulatory nucleosome.

DNA sequences from the long terminal repeat of the mouse mammary tumor virus (MMTV-LTR) position nucleosomes both in vivo and in vitro. Here, were present chromatin reconstitution experiments showing that MMTV-LTR sequences from -236 to +204 accommodate two histone octamers in positions compatible with the in vivo data. This positioning is not influenced by the length of the DNA fragment and occurs in linear as well as in closed circular DNA molecules. MMTV-LTR DNA sequences show an intrinsic bendability that closely resembles its wrapping around the histone octamer. We propose that bendability is responsible for the observed rotational nucleosome positioning. Translational nucleosome positioning seems also to be determined by the DNA sequence. These data, along with the results from reconstitution experiments with insertion mutants, support a modular model of nucleosome phasing on MMTV-LTR, where the actual positioning of the histone octamer results from the additive effect of multiple features of the DNA sequence.

Base Sequence↗