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At least 19 recordsLinked to original sources
PubMed1976

Structural proteins in the myofilaments and regulation of contraction in vertebrate smooth muscle.

The contractile systems of vertebrate smooth and striated muscles are compared. Smooth muscles contain relatively large amounts of actin and tropomyosin organized into thin filaments, and smaller amounts of myosin in the form of thick filaments. The protein contents are consistent with observed thin:thick filament ratios of about 15-18:1 in smooth compared to 2:1 in striated muscle. The basic characteristics of both types of contractile proteins are similar; but there are a variety of quantitative differences in protein structures, enzymatic activities and filament stabilities. Biochemical and X-ray diffraction data generally support recent ultrastructural evidence concerning the organization of the myofilaments in smooth muscle, although a basic contractile unit comparable to the sarcomere in striated muscle has not been discerned. Myofilament interactions and contraction in smooth muscle are controlled by changes in the Ca2+ concentration. Recent evidence suggests the Ca2+-binding regulatory site is associated with the myosin in vertebrate smooth muscle (as in a variety of invertebrate muscles), rather than with troponin which is the regulatory protein associated with the thin filament in vertebrate striated muscle.

Actomyosin↗
PubMed1977

Analysis of intracellular feline leukemia virus proteins II. Generation of feline leukemia virus structural proteins from precursor polypeptides.

The synthesis and processing of feline leukemia virus (FeLV) polypeptides were studied in a chronically infected feline thymus tumor cell line, F-422, which produces the Rickard strain of FeLV. Immune precipitation with antiserum to FeLV p30 and subsequent sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) were used to isolate intracellular FeLV p30 and possible precursor polypeptides. SDS-PAGE of immune precipitates from cells pulse-labeled for 2.5 min with [35S]methionin revealed the presence of a 60,000-dalton precursor polypeptide (Pp60) as well as a 30,000-dalton polypeptide. When cells were grown in the presence of the proline analogue L-azetidine-2-carboxylic acid, a 70,000-dalton precursor polypeptide (Pp70) was found in addition to Pp60 after a 2.5-min pulse. The cleavage of Pp60 could be partially inhibited by the general protease inhibitor phenyl methyl sulfonyl fluoride (PMSF). This partial inhibition was found to occur only if PMSF was present during pulse-labeling. Intracellular Pp70 and Pp60 and FeLV virion p70, p30, p15, p11, and p10 were subjected to tryptic peptide analysis. The results of this tryptic peptide analysis demonstrated that intracellular Pp70 and virion p70 were identical and that both contained the tryptic peptides of FeLV p30, p15, p11, and p10. Pp60 contained the tryptic peptides of FeLV P30, P15, and P10, but lacked the tryptic peptides of P11. The results of pactamycin gene ordering experiments indicated that the small structural proteins of FeLV are ordered p11-p15-p10-p30. The data indicate that the small structural proteins of FeLV are synthesized as part of a 70,000-dalton precursor. A cleavage scheme for the generation of FeLV p70, p30, p15, p11, and p10 from precursor polypeptides is proposed.

Azetidinecarboxylic Acid↗
PubMed2026

Uncovering viral protein acquisition events and human-specific folds with pairwise comparisons of predicted protein structures.

Pairwise sequence comparisons are at the center of molecular evolutionary analyses. However, viral pairwise comparisons are challenging because extreme mutation rates and evolutionary pressure cause genomes to diverge rapidly, limiting detectable sequence similarity to fewer than 3% of virus pairs. To overcome these limitations, we compared viruses based on structural similarity, using predicted protein structures from ColabFold and Foldseek to define protein fold clusters. We represented each virus genome by its protein structural content. Pairwise similarities between viruses were then quantified using the Jaccard index based on the presence or absence of protein fold clusters. Using a recently established viral protein fold database, we compared all pairs of eukaryotic viruses in RefSeq. This approach increased the proportion of comparable viral genome pairs from 2.4% to 16.5%. Using this protein-fold representation of viruses, we were able to accurately predict viral families with an average sensitivity of 85.9%. Investigation of viral families showing limited sensitivity with this approach uncovered a laterally transferred structural cluster (Rep/NS1) broadly shared across diverse viral families and found in the avian lineage of adenoviruses. Sequence homology suggests that this Rep was acquired from Parvoviridae, but the protein is mutant in the ATPase active site, indicating possible exaptation toward a purely DNA-binding function. In Gammapapillomaviruses, several E4 clusters were associated with human tropism. In summary, by representing viruses with structural protein clusters, we can classify highly divergent viruses, trace lateral gene transfer, and uncover features associated with viral host range.

Humans↗
PubMed1979

Amino-terminal sequence of bovine leukemia virus major internal protein: homology with mammalian type C virus p30 structural proteins.

The amino acid composition, the COOH-terminal amino acid, and the NH2-terminal amino acid sequence of the first 55 residues of the major internal structural protein, p24, of bovine leukemia virus (BLV) were determined. The compositional data and the results of end-group analysis revealed that, although BLV p24 is chemically distinct, it more closely resembles the p30 structural proteins than the other gag gene products of mammalian retroviruses. It was found that BLV p24 shares the common NH2-terminal proline and COOH-terminal leucine but lacks the common prolylleucylarginine tripeptide and the larger conserved region found near the NH2 terminus of all mammalian type C viral p30s. Alignment of the amino acid sequence of BLV p24 with the previously determined sequence of feline leukemia virus p27 revealed a statistically significant sequence homology. A more distant relationship was found between BLV p24 and other mammalian p30s. The finding of a definite sequence homology between BLV p24 and mammalian type C virus p30s clearly establishes the origin of these contemporary viral proteins from common progenitor genes.

Amino Acid Sequence↗
PubMed1975

Translation of the genes for the structural proteins of alphaviruses.

Synthesis of the structural proteins of Semliki Forest virus by a cell-free system derived from mouse L-cells and programmed by intracellular 26S RNA is described. This polycistronic RNA is translated in vitro into several discrete polypeptides. The identity of these polypeptides as the structural proteins of the virus was established by polyacrylamide gel electrophoresis, immunoprecipitation and tryptic peptide mapping. Studies using formyl--e135S]methionyl-tRNAf as precursor, and using diphtheria toxin and NAD to inhibit elongation, showed that 26S RNA contains only a single initiation site at, or near, the 5' end of the core protein cistron. Experiments in infected cells under conditions of synchronous initiation revealed that the order of the structural protein genes in 26S RNA is core-E3-E2-E1 in the 5' leads to 3' direction.

Arboviruses↗
PubMedDate not supplied

[Lambdoid phage structural proteins and antigens].

The composition of structural proteins of lambdoid phages such as lambda, phi 80 434 divided by molecular weights was determined by means of SDS-disc-electrophoresis in a 15% polyacrylamide gel. The proteins of the same phages were divided by isoelectric points using an isoelectric focusing in a 5,25% polyacrylamide gel with 8 M urea and a gradient pH 7.0--3.5. The both methods brought out a composition character of the virion proteins and illustrated the high degree of similarity among the structural proteins of phages lambda and 434 and a far less similarity among the proteins lambda and phi 80. The antigenic composition of the lambdoid phage was determined and the basic antigenes were identified on one-dimensional and two-dimensional immunoelectrophoregrams. The appreciable immunochemical affinity of basic antigenes of the lambda and 434, but a partial affinity of the phages lambda and phi 80 were found. The basic protein of the head pE proved to be immunochemically similar for all three phages.

Antigens, Viral↗
PubMed1979

Counteraction of urea destabilization of protein structure by methylamine osmoregulatory compounds of elasmobranch fishes.

Intracellular fluids of marine elasmobranchs (sharks, skates and rays), holocephalans and the coelacanth contain urea at concentrations averaging 0.4m, high enough to significantly affect the structural and functional properties of many proteins. Also present in the cells of these fishes are a family of methylamine compounds, largely trimethylamine N-oxide with some betaine and sarcosine, and certain free amino acids, mainly beta-alanine and taurine, whose total concentration is approx. 0.2m. These methylamine compounds and amino acids have been found to be effective stabilizers of protein structure, and, at a 1:2 molar concentration ratio of these compounds to urea, perturbations of protein structure by urea are largely or fully offset. These counteracting effects of solutes on proteins are seen for: (1) thermal stability of protein secondary and tertiary structure (bovine ribonuclease); (2) the rate and extent of enzyme renaturation after acid denaturation (rabbit and shark lactate dehydrogenases); and (3) the reactivity of thiol groups of an enzyme (bovine glutamate dehydrogenase). Attaining osmotic equilibrium with seawater by these fishes has thus involved the selective accumulation of certain nitrogenous metabolites that individually have significant effects on protein structure, but that have virtually no net effects on proteins when these solutes are present at elasmobranch physiological concentrations. These experiments indicate that evolutionary changes in intracellular solute compositions as well as in protein amino acid sequences can have important roles in intracellular protein function.

4-Chloro-7-nitrobenzofurazan↗
PubMed1978

Prediction of protein structure from amino acid sequence.

In principle, it is possible to predict theoretically the three-dimensional structure of a protein from its amino acid sequence. Recently substantial progress towards this goal has been made by the use of simple models to represent protein conformation and interatomic interactions, together with the knowledge gained form analyses of know protein structures.

Amino Acid Sequence↗
PubMed1978

Amino-terminal sequence analysis of the structural proteins of Sindbis virus.

The structural proteins of Sindbis virus, an enveloped virus which belongs to the Togavirus family, have been subjected to automated Edman degradation using improved techniques. Extensive NH2-terminal sequences of about 50 residues were determined for each of the two membrane glycoproteins. In both cases the NH2 terminus of the molecule was found to be similar in composition to typical water-soluble proteins. The viral capsid protein was found to have a blocked alpha-amino group. This is consistent with other observations that viral proteins derived from the NH2 terminus of precursor molecules are often blocked.

Amino Acid Sequence↗
PubMed1979

Tryptic peptide analysis of the structural proteins of a temperature-sensitive mutant derived from an HVJ (Sendai virus) carrier culture.

The individual structural polypeptides of HVJ (haemagglutinating virus of Japan--the Sendai strain of parainfluenza 1 virus) were examined by tryptic peptide analysis. [3H]-methionine-labelled structural proteins of the wild-type virus of HVJ (HVJ-W) and [35S]-methionine-labelled corresponding constituent proteins of a temperature-sensitive (ts) mutant (HVJ-pB) derived from an HVJ carrier culture were compared by ion-exchange chromatography on columns of P-type chromobeads. The tryptic peptides of the individual structural proteins showed characteristic elution profiles. In all the structural proteins tested, the chromatographic elution profiles of both strains generally showed a close resemblance. However, certain minor peaks which were present in one strain but absent in the other strain were detected in the preparations of the P, HN, and F polypeptides. Further, analysis of the NP polypeptide showed that a major peak of one strain appeared at a position in the pH gradient different from a seemingly corresponding major peak of the other strain. In the M protein some possibly homologous minor peaks were found to differ between the two strains.

Mutation↗
PubMed2026

The Sigma1 ER membrane receptor promotes structural protein folding and genome packaging of dengue virus.

Dengue virus (DENV) exploits the host endoplasmic reticulum (ER) to support viral protein translation and folding, replication, and assembly, although the identity of ER factors that promote these distinct steps during infection remain unclear. Here we demonstrate that the ER-resident Sigma1 ER membrane receptor (S1R) promotes virus structural protein folding and genome packaging of DENV during infection. Under S1R knockdown (KD), DENV infection is impaired without compromising virus translation or replication. Strikingly, EM analysis revealed that DENV particles in and secreted from S1R-depleted cells are smaller, likely because they are empty particles devoid of the vRNA genome. Biochemical experiments demonstrated that S1R binds to the prM structural protein and under S1R KD, the prM, E and C structural proteins became detergent-insoluble. Thus, without S1R, all three virus structural proteins misfold, impairing efficient genome packaging. Together, these findings identify a novel ER chaperone that supports a critical DENV infection step.

Dengue Virus↗
PubMed1977

Analysis of murine C-type virus structural proteins by rocket and crossed immunoelectrophoresis.

We have examined the structural proteins of Rauscher murine leukemia virus (R-MuLV) by means of rocket immunoelectrophoresis and crossed immunoelectrophoresis, using polyspecific antisera to Tween/ether-disrupted purified R-MuLV. Fifteen different precipitation lines were recognized in virus lysates. Using five reference antisera prepared to purified R-MuLV-structural proteins, the precipitation lines of p 10, p 15, p 30 and gp 69/70 were identified. These techniques, although less sensitive than radioimmunoassay, have several advantages, such as simplicity, direct control of precipitation reactions and possibility of using crude antigen preparations.

Animals↗
PubMed1975

Synthesis and turnover of intracisternal A-particle structural protein in cultured neuroblastoma cells.

Synthesis and turnover of the main structural protein (P73) of intracisternal A-particles were studied in mouse neuroblastoma cells in tissue culture. Triton X-100:EDTA-insoluble pellets containing 95% of the A-particle antigen in the cells were prepared and analyzed by electrophoresis in Na dodecyl-SO4-minus polyacrylamide gels. A 73,000 molecular weight component was prominent in pellets from three lines of neuroblastoma which contain numerous A-particles and this component was identified as the A-particle structural protein P73. It was absent in pellets prepared from cells which do not contain A-particles. Incorporation of labeled amino acids into P73 represented approximately 1.2% of total cell incorporation and this proportion did not change when the cell growth changed from log phase to stationary phase. Label appeared P73 within 2 min after radioactive amino acids were added to the medium. Pulse-chase and inhibitor studies confirmed antigenic measurements in demonstrating that the pool of P73 not assembled into A-particles was small. Turnover studies showed that P73 gained and lost label more rapidly than the average cell protein. In one cell line which was thoroughly characterized, approximately 60% of the main A-particle protein was estimated to turn over in a 24-hour period. Although the cells released approximately 10% of the proteins synthesized into the culture fluid, A-particle protein did not appear to be released. Analysis of culture fluid failed to reveal A-particles, soluble A-particle proteins, or A-particle antigen. It appears, therefore, that the particles are relatively rapidly synthesized and degraded, and that turnover occurs entirely intracellularly.

Animals↗
PubMed1977

Assembly of Bacillus subtilis phage phi29. 1. Mutants in the cistrons coding for the structural proteins.

The effect of mutations in the cistrons coding for the phage structural proteins has been studied by analyzing the phage-related structures accumulated after restrictive infection. Infection with susmutants in cistron 8, lacking both the major head and the fiber protein, does not produce any phage-related structure, suggesting a single route for the assembly of phage phi29; infection with ts mutants in this cistron produces isometric particles. Mutants is cistron 9, coding for the tail protein, TP1, produce DNA-free prolate heads with an internal core; these particles are abortive and contain the head proteins HPO, HP1 and HP3, the upper collar protein NP2 and the nonstructural proteins p7, p15 and p16. Mutants in cistron 10, coding for the upper collar protein, NP2, produce DNA-free isometric heads also with an internal core; they contain the head proteins and the nonstructural protein p7, suggesting that this protein forms the internal core. Mutants in cistrons 11 and 12, coding for the lower collar protein, NP3, and the neck appendages, NP1, respectively, give rise to the formation of DNA-containing normal capsids and DNA-free prolate particles, more rounded at the corners than the normal capsids and with an internal core; the DNA-containing 11-particles are formed by the head proteins and the upper collar protein; the DNA-free 11-particles contain, besides these proteins, the nonstructural protein p7 and a small amount of proteins p15 and 16. The DNA-containing 12-particles have all the normal phage structural proteins except the neck appendages, formed by protein NP1; the DNA-free particles are similar to the DNA-free 11-particles. After restricitive infection mutant sus14(1241) has a delayed lysis phenotype and produces a phage burst higher than normal, after artificial lysis. It produces DNA-containing particles, identical to wild-type phage, which have all the normal phage structural proteins, and DNA-free prolate particles, more rounded at the corners than the final phage particles and with an internal core; the last particles contain the same proteins as the DNA-free 11 or 12-particles. These particles could represent a prohead state, ready for DNA encapsulation. None of the DNA-containing particles have the nonstructural proteins p7, p15 or p16, suggesting that these proteins are released from the proheads upon DNA encapsulation.

Bacillus subtilis↗
PubMed1977

Feline leukemia virus: biochemical and immunological characterization of gag gene-coded structural proteins.

The major non-glycosylated structural proteins of feline leukemia virus have been isolated, and competition immunoassays have been developed for each. These proteins include the 27,000- to 30,000-molecular-weight major internal antigen designated p30, a 15,000-molecular-weight protein (p15), an acidic protein of 12,000 molecular weight (p12), and a highly basic 10,000-molecular-weight protein (p10). Immunologically and biochemically corresponding proteins of feline and murine leukemia viruses have been identified. and, on the basis of analogy to the known sequence of a prototype type C virus of mouse origin, the map order of the gag region of the feline type C viral genome has been tentatively deduced as NH2-p15-p12-p10-COOH. The demonstration of two feline leukemia virus gag gene-coded proteins, p15 and p12, expressed in the form of an uncleaved precursor in a mink cell line nonproductively transformed by feline sarcoma virus provides indirect support for the proposed sequence.

AKR murine leukemia virus↗