Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:Q07644 (polypeptide)
 72,197 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Xenopus fibrinogen is distinct from that of mammals in that the B beta subunit of the secreted protein has a higher apparent molecular weight than either the A alpha or the gamma subunit. A precursor polypeptide for each subunit was identified among the products translated in vitro from liver mRNA. Pre-A alpha is larger than pre-B beta and pre-gamma is the smallest of the three. Purified liver parenchymal cells cultured in the presence of tunicamycin secrete fibrinogen polypeptides which lack carbohydrate moieties. Our analysis of these forms of Xenopus fibrinogen demonstrated the presence of a signal peptide on each of the precursor polypeptides, the loss of a COOH-terminal peptide from the pre-A alpha chain, and the presence of one carbohydrate moiety on the mature gamma chain and two carbohydrate moieties on the mature B beta chain. The B fibrinopeptide on the NH2-terminus of the B beta chain is unusually large. The number of amino acids in this peptide is approximately twice that characteristic of mammalian B fibrinopeptides and it is glycosylated. On the basis of these data, together with information in the literature, we propose that when vertebrates first arose the B fibrinopeptide was a large glycosylated peptide. It retained this basic structure during the evolution of all subsequent vertebrates, with the exception of mammals. In contrast, the A fibrinopeptide increased in length early in vertebrate evolution. The alpha portion of the A alpha subunit of fibrinogen appears to have originally been a polypeptide about the same length as the beta chain. Concomitant with the evolution of mammals, the alpha polypeptide significantly increased in length.
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PMID:Xenopus fibrinogen synthesis and secretion. Analysis of precursor polypeptides and their post-translational modification. 670 77

Pyruvate carboxylase from Pseudomonas citronellolis is composed of non-identical subunits which include a larger biotin-containing polypeptide (alpha) of Mr = 65,000, and a smaller biotin-free polypeptide (beta) of Mr = 54,000. We have investigated these two polypeptides by analyzing their amino acid composition, cyanogen bromide peptide maps, and immunochemistry. The results showed that the subunits of the enzyme have quite different properties. Antibodies prepared against the polypeptides were used as probes of the catalytic functions of the subunits. Immunotitration studies indicated that only anti-alpha inhibited enzyme activity. The antibiotin fraction of this antibody population was removed by passage through biotin-Sepharose (anti-alpha'). Titration curves using anti-alpha' showed identical inhibition when total pyruvate carboxylase activity, ATP/Pi exchange activity, and pyruvate/oxalacetate exchange activity were measured, suggesting that both active sites are located on the alpha polypeptide. The arrangement of the subunits in the quaternary structure was investigated by means of the surface probe carbonic anhydrase linked to toluene isocyanate, and by partial digestion experiments with trypsin, chymotrypsin, and pronase. The results indicated that the alpha polypeptides are on the outside of the molecule and the beta polypeptides are the internal subunits.
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PMID:Characterization of the subunit structure of pyruvate carboxylase from Pseudomonas citronellolis. 679 93

Metallothionein purified from the livers of rats injected with CdCl3 was cleaved by proteolysis into a 32-residue polypeptide that contained 4 bound Cd ions. Appearance of this fragment designated alpha requires prior treatment of metallothionein with EDTA to remove the Zn ions and destabilize the 3-metal cysteine cluster in the other domain. The half-molecule domain was not efficiently produced by proteolysis of native metallothionein. The Cd4-alpha fragment is asymmetric in shape, as is the parent molecule. NH2-terminal sequence analysis revealed that the alpha fragment starts at Lys 30. Since the same amino acids are released from the COOH terminus of intact thionein and the alpha fragment by carboxypeptidase Y, the alpha domain generated by digestion with subtilisin therefore comprises residues 30 through 61. The amino acid composition of the alpha polypeptide is consistent with the structure of the 4-metal cysteine cluster proposed by Otvos and Armitage ((1980) Proc. Natl. Acad. Sci. U. S. A. 77, 7094-7098). Metallothionein appears to consist of a 3-metal cysteine domain in the NH2-terminal half of the thionein molecule and the 4-metal cysteine domain in the COOH-terminal half.
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PMID:Domain nature of metallothionein. 680 Oct 48

Previous studies of the B5.C-H-2 bm12 (bm12) strain have demonstrated the presence of a mutation localized to the I-A subregion of the mouse H-2 major histocompatibility complex. This mutation has been shown to be responsible for defects in Ir-gene function in Ia and MLR determinants. A comparison of the molecular size of the bm12 mutant and the parental B6 Ia-antigen component polypeptides failed to demonstrate any differences in the alpha and beta polypeptides. Thus, no major structural additions for deletions are present in the Ia alpha and beta chain polypeptide or carbohydrate structure. A significant decrease in the amount of invariant (31K) polypeptide was, however, consistently observed in the bm12 Ia antigen preparations. Tryptic peptide comparisons of 14C B6 and 3H bm 12 alpha and beta polypeptides demonstrated a limited number of peptide differences in the bm 12 beta polypeptide but none in the bm12 alpha polypeptide. The significance of these biochemical mutations and altered biological phenomena are discussed in relation to a model of the immunological interaction sites on Ia antigens.
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PMID:Tryptic peptide comparison of Ia antigen alpha and beta polypeptides from the I-A mutant B6.C-H-2bm12 and its congenic parental strain B6. 694 71

Phycoerythrin 545 is a biliprotein having a polypeptide structure of alpha 2 beta 2, and each alpha and beta polypeptide has chromophores. Circular dichroism (CD) and absorption spectroscopy in the visible region together with various biochemical protocols have been used to study these chromophores. The CD spectrum exhibits overlapping positive and negative bands. Exciton splitting between closely-spaced pairs of chromophores produces a CD spectrum that has positive and negative bands of equal rotational strengths, a conservative spectrum. Alternatively, any positive or negative band could arise from a single chromophore. The results of this study demonstrate that exciton splitting is the likely cause of the negative and corresponding positive bands. The CD spectra of the separated alpha and beta polypeptides, under conditions where the polypeptide structure is denatured, have no negative bands. When the polypeptides are allowed to refold individually, the chromophores on the beta polypeptide regain a combination of negative and positive CD bands. The spectrum of the alpha polypeptide shows no evidence of exciton splitting under these refolding conditions. In another approach, urea is added to the protein in low concentrations, which result in changes in the conformation and perhaps association of the protein. A difference CD spectrum of native protein minus protein in 0.8 M urea shows a spectrum characteristic of exciton splitting. Moreover, the remaining CD spectra in 0.8, 1.6, or 2.4 M urea still show the possibility of further exciton splitting, but a slightly different wavelengths from the spectrum that is deleted by 0.8 M urea. This finding may suggest that there are two types of exciton splitting.
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PMID:Exciton splitting in phycoerythrin 545. 792 46

Here, we present evidence that glycoprotein (GP) Ib alpha, one of three polypeptides that make up the GP Ib--IX complex--the receptor for von Willebrand factor (vWf) on the surface of unactivated platelets--is modified by sulfation of tyrosine residues. Only GP Ib alpha was found to incorporate 35S when the GP Ib--IX complex was immunoprecipitated from [35S]sulfate metabolically labeled L and CHO cells that express the recombinant complex. The occurrence of sulfation on tyrosine residues of the polypeptide backbone was determined by removing O- and N-linked oligosaccharides. Limited proteolytic digestion of metabolically labeled GP Ib alpha revealed that sulfated tyrosine residues are located in the 45-kDa globular region containing the vWf binding site. By mutating potentially sulfated tyrosine residues to phenylalanine and comparing the stoichiometry of sulfate incorporation of these mutants to the incorporation in wild-type GP Ib alpha, three clustered tyrosine residues--Tyr-276, Tyr-278, and Tyr-279-were identified that undergo the modification. Culturing cells in sulfate-depleted medium containing sodium chlorate and guaiacol completely inhibited GP Ib alpha sulfation but did not decrease GP Ib-IX expression on the cell surface. Similarly, transiently transfected CHO cells expressed the mutant GP Ib alpha polypeptide on their surfaces at the same levels as they expressed wild-type GP Ib alpha. These results suggest that tyrosine sulfation of GP Ib alpha has little or no effect on the synthesis, assembly, and surface expression of the GP Ib-IX complex. Nevertheless, inhibiting sulfation of GP Ib alpha reduced the binding of 125I-labeled vWf in the presence of ristocetin by up to 37%.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Tyrosine sulfation of the glycoprotein Ib-IX complex: identification of sulfated residues and effect on ligand binding. 794 1

The core antenna/reaction-centre complex RC-B875 and the peripheral antenna complex B800-850 of the two strains DSM 149 and DSM 151 of the purple non-sulphur bacterium Rhodocyclus gelatinosus have been isolated from photosynthetic membranes by means of lauryl-N,N-dimethyl-amineoxide as a detergent and subsequent sucrose-gradient centrifugation. The two complexes were characterised spectroscopically by absorption and circular dichroism (CD) spectroscopy at room temperature. CD measurements revealed very weak signals for the core antenna B875 whereas for the peripheral antenna B800-850, a strong biphasic CD signal was observed, attributable to the B850 pigments. There is apparently no CD signal present for the B800 pigments. The core and the peripheral antenna complex are built up by a distinct alpha/beta-polypeptide pair. The pigment/protein ratio in the peripheral antenna complex is 3 bacteriochlorophyll/(alpha/beta)-polypeptide pair. The amino acid sequences of the alpha and beta polypeptides of both complexes from the two strains of Rc. gelatinosus were established by automated Edman degradation, chemical and enzymic digestion, amino acid composition analyses and carboxypeptidase digestion. In the case of the beta polypeptides, the amino acid sequence determination was confirmed by ion-spray MS of the isolated antenna apoproteins. The inter-strain (DSM 149 and 151) positional identity between the equivalent apoproteins is extremely large and varies in the range 90-100%. The B875-beta polypeptide from Rc. gelatinosus exhibits shortened C-termini, as detected for the analogous antenna apoproteins of Rhodobacter sphaeroides and Rhodobacter capsulatus, which can be correlated with weak core antenna near-infrared CD signals. However, the B800-850-alpha polypeptide of Rc. gelatinosus, with 71 amino acids, exhibits an extended C-terminal portion indicative of the formation of a second transmembrane domain, which so far has not been observed for bacterial antenna apoproteins. This part of the molecule is extremely rich in alanine and proline residues. All the sequenced antenna apoproteins of Rc. gelatinosus exhibit a characteristic membrane-buried histidine which is thought to ligate the B875 or the B850 pigments. In the B800-850-beta apoprotein, a second, so far beta-antenna-apoprotein-specific histidine, is replaced by a glutamine residue. A careful inspection of the determined antenna structures of Rc. gelatinosus revealed some remarkable structural similarities within presumed cofactor-binding sites of Fe-S-type-reaction-centre apoproteins, indicating possible basic structural motifs for complexing bacteriochlorophyll molecules.
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PMID:Structural and spectral characterisation of the antenna complexes of Rhodocyclus gelatinosus. Indications of a hairpin-like-arranged antenna apoprotein with an unusually high alanine content. 802 May 5

The genes for the proton-translocating nicotinamide nucleotide transhydrogenase from Rhodospirillum rubrum have been cloned using a probe constructed with the polymerase chain reaction, genomic DNA as target and oligonucleotide primers corresponding to amino acid sequence obtained from the purified soluble subunit. There is a cluster of three genes, designated pntAA, pntAB and pntB, whose translation products indicate polypeptides of 384, 139 and 464 amino acids, respectively. This contrasts with the situation in the enzymes from Escherichia coli (two polypeptides) and bovine mitochondria (one polypeptide) but there is close similarity between the sequences. PntAA is the soluble subunit of the enzyme from R. rubrum, equivalent to the relatively hydrophilic domain I that forms the N-terminal part of the alpha polypeptide of E. coli transhydrogenase and which probably contains the NAD(H)-binding site. PntAB corresponds to the strongly hydrophobic domain IIa at the C-terminus of the alpha polypeptide of the E. coli transhydrogenase. PntB corresponds to the E. coli beta polypeptide, which comprises the strongly hydrophobic domain IIb and the relatively hydrophilic domain III, thought to contain the NADP(H)-binding site. The peptide bond between PntAA-Lys237 and -Glu238 of both the denatured and the native soluble subunit is very sensitive to proteolysis by trypsin and the neighbouring peptide bond Lys227-Thr228 to cleavage by the endoproteinase Lys-C. Related sites have been reported to be sensitive to trypsin in the E. coli and bovine mitochondrial enzymes. The two tryptic fragments from the native R. rubrum soluble subunit are unable to reconstitute transhydrogenase activity to membranes depleted of the soluble subunit but they can block reconstitution by intact soluble subunit. It is suggested that this protease-sensitive region separates two subdomains and that, after trypsinolysis, at least one retains structural integrity and can dock with domains II and/or III.
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PMID:Cloning and sequencing of the genes for the proton-translocating nicotinamide nucleotide transhydrogenase from Rhodospirillum rubrum and the implications for the domain structure of the enzyme. 807 1

Purified phosphofructokinase 1 from baker's yeast (Saccharomyces cerevisiae) was subjected to proteolysis by thermolysin, endoproteinase lys-C, trypsin and chymotrypsin under defined solvent conditions. In the absence of substrates and allosteric effectors, the catalytic activity of phosphofructokinase rapidly disappeared in the presence of each proteolytic enzyme. The presence of a saturating concentration of ATP protected phosphofructokinase activity from proteolytic inactivation while the collective presence of fructose 6-phosphate, AMP and fructose 2,6-bisphosphate provided transient activation during proteolysis. Changes in the quaternary structure of phosphofructokinase resulting from proteolysis were estimated by high performance size exclusion chromatography while changes in the primary sequence of the individual alpha and beta polypeptide chains were estimated by polyacrylamide-gel electrophoresis in sodium dodecylsulfate. The site(s) of proteolytic cleavage were identified by N-terminal sequence analysis of resolved electrophoretic components. The presence of ATP protects phosphofructokinase from thermolysin proteolysis, while the collective presence of fructose 6-phosphate, AMP and fructose 2,6-bisphosphate restricts proteolysis to one site in each polypeptide chain involving the peptide bonds preceding Leu199 in the alpha chain and Leu192 in the beta chain. The truncated phosphofructokinase retains its octameric structure. The presence of ATP largely restricts endoproteinase lys-C proteolysis to a single site in the alpha chain involving the peptide bond preceding Val914. This cleavage results in the dissociation of the octameric form of phosphofructokinase into two tetramers. The presence of ATP restricts both trypsin and chymotrypsin proteolysis to the N-terminal and C-terminal regions described above, resulting in the preferential stabilization of the tetrameric form of phosphofructokinase. It would appear that the first 200 and last 80 residues which are unique to the sequence of the yeast phosphofructokinase are not directly involved in catalysis or its allosteric regulation. However, the last 80 residues of the alpha polypeptide chain do appear to stabilize an octameric structure which is unique to yeast phosphofructokinase.
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PMID:Limited proteolysis of yeast phosphofructokinase. Sequence locations of cleavage sites created by the actions of different proteinases. 822 96

Residue Asp60 of the tryptophan synthetase alpha chain of Escherichia coli is though to interact with the pyrrole NH of substrate indole-3-glycerol phosphate and facilitate its cleavage to indole and glyceraldehyde 3-phosphate. Two distinguishable partial revertants of DN60 tryptophan synthetase alpha mutant trpA34 were analyzed. The slower growing partial revertant, PR1, had the second-site change, YD102. The other partial revertant, PR2, lacked three consecutive base pairs, resulting in replacement of Ala59 and Asn60 of the DN60 mutant alpha polypeptide by Asp. Inspection of the three-dimensional structure of the enzyme-substrate analog complex revealed that Tyr102 is in the vicinity of the pyrrole NH of the substrate. The PR1 alpha chain has a near normal Km for substrate, whereas the PR2 polypeptide has greatly reduced substrate affinity. The PR2 polypeptide is more active than the PR1 polypeptide in the alpha beta reaction in vitro and appears to be more active than the PR1 polypeptide in vivo. Attempts to obtain repeat occurrences of the PR2 deletion mutation were unsuccessful. A third type of trpA34 partial revertant, PR3, that grows very poorly in minimal medium, also has a Tyr102 replacement: YF102. These findings demonstrate that each of the second-site mutations affects a residue located in the vicinity of the active site residue altered by the primary mutation. Slightly leaky mutant trpA89, genetically altered near the site of the trpA34 mutation, was found to have a GS61 substitution.
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PMID:Partial revertants of tryptophan synthetase alpha chain active site mutant Asp60-->Asn. 846 31


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