Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:3.2.1.17 (lysozyme)
21,489 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

This research was undertaken to demonstrate that the protein-bound chromophores in aged human lens can act as sensitizers for protein damage by UVA light. The water-insoluble (WI) proteins from pooled human and bovine lenses were solubilized by sonication in water and illuminated with UV light similar in output to that transmitted by the cornea. Analysis of the irradiated proteins showed a linear decrease in sulfhydryl groups with a 30% loss after 2 h. No loss was seen when native alpha-crystallin was irradiated under the same conditions. A 25% loss of histidine residues was also observed with the human lens WI fraction, and sodium dodecyl sulfate polyacrylamide gels indicated considerable protein cross-linking. Similar photodamage was seen with a WI fraction from old bovine lenses. While the data show the presence of UVA sensitizers, some histidine destruction and protein cross-linking were also obtained with alpha-crystallin and with lysozyme, which argue that part of the histidine loss in the human WISS was likely due to tryptophan acting as a sensitizer. A preparation of human WI proteins was irradiated with a total of 200 J/cm2 of absorbed light at 10 nm intervals from 290 to 400 nm. Photodamage of cysteine SH groups (35%) and methionine (28%) was maximum at 330 nm and diminished linearly at longer wavelengths. The major loss of tryptophan (80%) occurred at 290 nm, but destruction was observed throughout the UVA range. Tyrosine was 35% destroyed at 290 nm but decreased sharply to only 5% at 330 nm.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:UVA photolysis using the protein-bound sensitizers present in human lens. 807 76

The new fMLP analog HCO-Hmb-Leu-Phe-OMe (1), containing (S)-2-hydroxy-4-(methylthio)butyric acid (Hmb) in place of L-methionine at the N-terminal position, has been synthesized and fully characterized. The peptide 1 has been designed in order to improve the understanding of the role exerted by the formamido group in the binding interaction with the formylpeptide chemotactic receptors. Chemotaxis, superoxide anion production, and lysozyme release have been measured for both 1 and its deformylated analog Hmb-Leu-Phe-OMe 2. Results indicate that a strong hydrogen bond of the OH....O = C type may complement a weak H-bonding interaction involving the formylic proton as H-bond donor.
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PMID:Synthesis and chemotactic activity of the fMLP analog HCO-Hmb-Leu-Phe-OMe. 821 43

To determine the effects of different amino acids on the structure and stability of an alpha-helix in the context of a globular protein, all 19 naturally-occurring amino acids were substituted for Ser44 in phage T4 lysozyme. A more restricted set of nine replacements was also made for Val131. Ser44 and Val131 are two of a very limited number of possible sites in T4 lysozyme that are well within alpha-helices, are solvent-exposed and relatively free of interactions with neighboring residues, and are not involved in crystal contacts. High resolution structures for the majority of the mutants, some of which crystallized non-isomorphously with wild-type, were determined. With the exception of proline, the amino acid substitutions caused little if any perturbation of the alpha-helix backbone. Also the beta-branched residues Thr, Val and Ile show no indication of either side-chain or backbone distortion. Therefore, other than proline, there is no evidence that differences in helix propensities are associated with different amounts of strain introduced into the helix. For reference, and also to allow estimates of side-chain entropy, a survey was made of side-chain conformations in 100 well-refined protein structures. As noted previously all side-chains within alpha-helices strongly avoid the g- conformation (chi 1 approximately 60 degrees). This restricts the beta-branched residues Thr, Val and Ile to a single conformer (g+, chi 1 approximately -60 degrees). Asp, Asn, Met and Ser within helices also overwhelmingly prefer the g+ conformation. For Arg, Cys, Gln, Glu, Leu and Lys the t (chi 1 approximately 180 degrees) and g+ conformers are populated roughly equally. Only the aromatic residues, His, Tyr, Trp and Phe prefer the t conformation. These preferences are the same whether the side-chain is buried or solvent-exposed. In general, the side-chain conformations adopted by the residues substituted at positions 44 and 131 correspond to the most commonly observed conformation for the same amino acid in helices in known protein structures. The changes in protein stability for the replacements at site 131 in general agree well with those at site 44 (correlation r = 0.97), suggesting that these may be representative of substitutions at fully solvent-exposed sites in the middle of alpha-helices. The free energy values also agree quite well with those observed for equivalent replacements in a number of soluble alpha-helical model peptides and with data from "host-guest" studies and statistical surveys (r = 0.69 to 0.93).(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Determination of alpha-helix propensity within the context of a folded protein. Sites 44 and 131 in bacteriophage T4 lysozyme. 828 84

The polarized secretion of newly-synthesized proteins of human tracheal submucosal gland cells was studied. Human tracheal gland cells were cultured on permeable filter supports allowing a separate biochemical analysis of apical and basal secretion. By transmission electron microscopy, confluent filter-grown cells were seen to form a continuous sheet of both multilayer and monolayer epithelial cells. Junctional complexes between adjacent cells were observed. On immunofluorescence microscopy, human tracheal gland cells in cultured exhibited characteristics of epithelial and secretory cells, including cytoplasmic staining for cytokeratin and for two secretory protein markers specific to the glandular serous type cell: lysozyme and antileucoprotease. [35S]methionine metabolic labelling experiments demonstrated that at least 90% of newly-synthesized secretory proteins were recovered in the apical medium. Moreover, lysozyme secretion was strongly polarized since 85% was released into the apical medium. Conversely, antileucoprotease secretion was more bidirectional since nearly 40% of released antileucoprotease was present in the basal medium. The fact that these two secretory proteins are released with differing relative polarity emphasizes that human tracheal gland cells exhibit at least two different exocytotic routing operations.
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PMID:Vectorial delivery of newly-synthesized secretory proteins by human tracheal gland cells in culture. 834 52

Changes in biological properties of serum albumin, egg white lysozyme, human serum alpha-1 antiproteinase and human leukocyte ribonuclease in effect of interaction with the enzyme system composed of myeloperoxidase from human neutrophilic polymorphonuclear leukocytes, Cl- and H2O2 were investigated. All the studied proteins lost their biological functions and were denaturated, but the amounts of hydrogen peroxide necessary to produce these effects differed remarkably for each individual protein. The alpha-1 antiproteinase ability of binding to trypsin was abolished upon employing 1.2 mols of H2O2 per mol of alpha-1 antiproteinase. The lysozyme enzymatic activity was abolished when 1.4 mols of H2O2 per mol of lysozyme were employed. Albumin decreased its binding to specific antialbumin antibodies and entirely lost the binding properties when 2 mols and about 10 mols of H2O2 per mol of albumin were employed, respectively. On the other hand 18 mols of H2O2 per mol of human leukocyte ribonuclease were necessary to inactivate this enzyme. All the mentioned proteins were protected from losing their biological functions by excess of specific amino acids with affinity to hypochlorite: Alpha-1 antiproteinase by excess of N-acetylmethionine, lysozyme by N-acetylmethionine and N-acetyl glycyltryptophane, albumin by N-acetyl derivatives of methionine, cysteine, tryptophane and lysine, whereas ribonuclease was protected from denaturation by all above mentioned amino acid derivatives. None of the studied proteins was protected from denaturation by N-acetyl tyrosine, or phenylalanine.
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PMID:Inactivation and denaturation of some proteins by enzyme system: myeloperoxidase, chloride and hydrogen peroxide. 840 71

In this study, native cells of Streptococcus mutans VA-29R and Streptococcus rattus FA-1 displayed significantly higher aminopeptidase activity than did cells of Streptococcus cricetus AHT or Streptococcus sobrinus 6715 toward the nitroanilide derivatives of leucine, alanine, methionine, arginine, and lysine. These differences in cellular aminopeptidase activity led us to investigate the subcellular localization of the aminopeptidase in these mutans group streptococci. Following conversion of native cells to protoplasts by treatment with lysozyme, most of the aminopeptidase activity detected in the native-cell preparations remained associated with the intact protoplasts. After lysis of protoplasts and differential centrifugation, most of the total cellular aminopeptidase activity was recovered with the cytoplasmic fraction. Membrane-associated aminopeptidases represented only minor activities in these mutans group streptococci. Although the four strains showed no differences with respect to a predominant cytoplasmic localization for the aminopeptidase activities, the levels of activity in the cytoplasmic fractions from S. cricetus AHT and S. sobrinus 6715 were significantly lower than those measurable in the corresponding fractions from S. mutans VA-29R and S. rattus FA-1. These results support the conclusion that the differences in aminopeptidase activity expressed by these streptococci reflect quantitative differences rather than differences in enzyme subcellular localization.
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PMID:Comparison of aminopeptidase activities in four strains of mutans group oral streptococci. 841 40

Using the catalytic mechanism of lysozyme as a paradigm for the mechanism of other enzymes that catalyze the hydrolysis of beta-1,4-glycosidic linkages, including chitinase, we have examined the effect of chemical modification with 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide (EDC) on the reaction catalyzed by Zea mays chitinase. Inactivation with EDC did not result in derivatization of essential carboxylic acid residues, but resulted in the selective modification of a single essential tyrosine residue (Verburg, J. G., Smith, C. E., Lisek, C. A., and Huynh, Q. K., 1991, J. Biol. Chem. 267, 3886-3893). Here, we examine the role of the homologous tyrosine residue in the catalytic mechanism of the Arabidopsis thaliana chitinase. Tyrosine-174 of the Arabidopsis chitinase was replaced, with phenylalanine, alanine, histidine, and methionine by site-directed mutagenesis, and the variant chitinases were expressed in insect cells using baculovirus transfer vectors. A comparison of the reaction catalyzed by each of the variant enzymes indicates that substitution of another amino acid for Tyr-174 alters, but does not eliminate, enzymatic activity. Estimates of the specific activities of the variant chitinases reveal that substitution of His for Tyr-174 has a minimal effect on catalysis, the specific activities of the Phe and Met variants are approximately equivalent to each other, but are 60% the specific activity of wild-type Arabidopsis chitinase, and the specific activity of the Ala variant is only 40% that of wild-type. The observation that the Arabidopsis chitinase is tolerant to mutagenesis at this position suggests that Tyr-174 does not participate directly in catalysis.
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PMID:Examination of the role of tyrosine-174 in the catalytic mechanism of the Arabidopsis thaliana chitinase: comparison of variant chitinases generated by site-directed mutagenesis and expressed in insect cells using baculovirus vectors. 842 56

Two bulky amino acids within the core of phage T4 lysozyme have each been replaced in turn with a series of hydrophobic amino acids. In one set of experiments, Leu99 was replaced with Phe, Met, Ile, Val and Ala. In the second series, Phe153 was replaced with Leu, Met, Ile, Val and Ala. The double mutant in which both Leu99 and Phe153 were replaced with alanine was also constructed. The change in stability of the protein associated with each substitution and the crystal structure of each variant have been determined. In the case of replacements at position 99 the protein behaves in a relatively rigid manner, and changes very little in response to substitutions. In contrast, the protein is more flexible and adjusts much more in response to substitutions of Phe153. In both cases there is a roughly linear dependence between the stability of the mutant protein relative to wild-type (delta delta G) and the difference in the hydrophobic strength of the amino acids involved in the substitution based on solvent transfer measurements (delta delta Gtr). The change in delta delta G is, however, much greater than delta delta Gtr. For the Phe153 replacements the discrepancy is about 1.9-fold, while for the Leu99 series it is about 2.6-fold. Mutants such as Leu99-->Ala, for which the protein remains essentially rigid, tend to create larger cavities and so incur a larger energy of destabilization. Mutants such as Phe153-->Ala, for which the protein structure tends to relax, result in smaller cavities and so are less destabilized. Mutants L99I and L99V are less stable than expected from considerations of transfer free energy and cavity formation due to introduced strain caused by the replacement of Leu99 with a residue of different shape. Mutant F153L is more stable than the reference wild-type, even though the transfer free energy of Leu is less than that of Phe. The increase in stability is apparently due to torsional strain in the side-chain of Phe153 that is present in wild-type lysozyme, but is relieved in the mutant structure.
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PMID:Similar hydrophobic replacements of Leu99 and Phe153 within the core of T4 lysozyme have different structural and thermodynamic consequences. 843 69

LL-H, a virulent phage of Lactobacillus delbrueckii subsp. lactis, produces a peptidoglycan-degrading enzyme, Mur, that is effective on L. delbrueckii, Lactobacillus acidophilus, Lactobacillus helveticus, and Pediococcus damnosus cell walls. In this study, the LL-H gene mur was cloned into Escherichia coli, its nucleotide sequence was determined, and the enzyme produced in E. coli was purified and biochemically characterized. Mur was purified 112-fold by means of ammonium sulfate precipitation and cation-exchange chromatography. The cell wall-hydrolyzing activity was found to be associated with a 34-kDa protein. The C-terminal domain of Mur is not essential for catalytic activity since it can be removed without destroying the lytic activity. The N-terminal sequence of the purified lysin was identical to that deduced from the nucleotide sequence, but the first methionine is absent from the mature protein. The N-terminal part of this 297-amino-acid protein had homology with several Chalaropsis-type lysozymes. Reduction of purified and Mur-digested L. delbrueckii cell wall material with labeled NaB3H4 indicated that the enzyme is a muramidase. The temperature optimum of purified Mur is between 30 and 40 degrees C, and the pH optimum is around 5.0. The LL-H lysin Mur is stable at temperatures below 60 degrees C.
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PMID:Genetic and biochemical characterization of the Lactobacillus delbrueckii subsp. lactis bacteriophage LL-H lysin. 852 15

A plasmid-borne gene encoding bacteriophage T4 lysozyme with a structural mutation, Tyr161-Ala, was mutagenized by by the use of polymerase chain reaction. The mutagenized gene was inserted into a specialized bacteriophage lambda cloning vector that must acquire a functional lysozyme gene in order to form plaques. Functional variants of the mutant lysozyme were selected. Three compensatory second-site revertants were obtained: Thr152-Met, Lys43-Ile, and Thr151-Ala. The effects of these mutations are interpreted in light of previous structural and genetic studies of T4 lysozyme.
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PMID:Second-site reversion of a structural defect in bacteriophage T4 lysozyme. 856 37


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