Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.2.1.23 (beta-galactosidase)
 14,648 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Coupling of ribonucleoprotein particles from L cells infected with vesicular stomatitis virus to a pre-incubated ribosomal system obtained from uninfected HeLa cells allowed synthesis of two proteins. G1 (molecular weight 63,000) and G2 (molecular weight 67,000), and all other proteins of vesicular stomatitis virus except the spike protein G (molecular weight 69,000). Analyses of the tryptic peptides showed that G1, G2, and G had identical peptide sequences. The synthesis of G2 required the presence of membranes; only G1 was synthesized in the absence of any membranes. G2 but not G1 was shown to be a glycoprotein by affinity chromatography on a concanavalin A-Sepharose column. Removal of sialic acid residues from G by neuraminidase resulted in a product having an identical mobility to G2. Digestion of G2 or G with a mixture of neuraminidase (EC 3.2.1.18), beta-galactosidase (EC 3.2.1.23), and beta-N-acetylglucosaminidase (EC 3.2.1.30), however, produced a protein of molecular weight 65,000. These data suggest that G2 is the desialated G and is formed by glycosylation of G1, which is the unglycosylated polypeptide backbone of G.
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PMID:Synthesis and glycosylation in vitro of glycoprotein of vesicular stomatitis virus. 19 4

We have characterized expression of beta-galactosidase from a plasmid cloning vehicle, pBGP120, which carries most of the lacZ gene and contains a single EcoRI site near the end of lacZ. In addition, we have examined expression of heterologous DNA inserted at the position of the EcoRI site. The EcoRI site was shown to be within the sequence coding for beta-galactosidase and its precise location and phase were deduced. Insertion of heterologous EcoRI-generated DNA fragments altered the molecular weight of the plasmid-encoded beta-galactosidase polypeptide. Those insertions that were in the correct phase were expressed at a high level as a fused protein. The different forms of beta-galactosidase polypeptides produced by various hybrid plasmids were all stable proteins. The level of expression of the plasmid-encoded beta-galactosidase was several times higher than maximal expression of chromosome-encoded beta-galactosidase, suggesting that expression is proportional to gene copy number. The expression of the plasmid lacZ gene was controlled by cyclic AMP. When grown in a cya strain (DG74), expression was dependent on exogenous cyclic AMP. Although in normal strains there was insufficient lac repressor to inactivate all copies of the plasmid, repressor regulation was restored when the plasmid was grown in a strain (M96) that overproduces the lac repressor.
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PMID:Regulated expression by readthrough translation from a plasmid-encoded beta-galactosidase. 20 72

The amino acid sequence of beta-galactosidase was determined. The protein contains 1021 amino acid residues in a single polypeptide chain. The subunit molecular weight calculated from the sequence is 116,248. The sequence determination, carried out mainly by conventional methods, was aided by complementation tests, by the use of termination mutant strains, and by a new immunochemical method. The five residue sequence Thr-Pro-His-Pro-Ala appears twice within the polypeptide chain, but no other striking homologous features are evident.
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PMID:The amino acid sequence of beta-galactosidase of Escherichia coli. 32 55

The energy source shift-down described in the preceding paper (Molin et al., J. Bacteriol. 131: 7-17, 1977) was used to study the effects of shift-down on protein synthesis. The overall rate of protein synthesis was reduced immediately, and to the same extent, in stringent and relaxed strains. The primary effect of the shift was a slowing down of the polypeptide chain growth rate, a finding not previously reported. In stringent strains the normal, preshift rate was reestablished within 2 to 3 min, whereas in relaxed strains the chain growth rate remained low for about 20 min before slowly returning to the normal value, which was reestablished some 50 to 60 min after the shift. Throughout this transition, the stability of messenger ribonucleic acid (mRNA) remained unchanged in both strains. We interpret these findings as evidence of the more rapid reduction of the mRNA pool in the stringent strain after shift-down: we believe that very soon after the shift, the stringent strain reduces its pool of mRNA and with it the number of ribosomes engaged in protein synthesis. In this manner the number of active ribosomes is adjusted to the availability of energy and carbon. The relaxed strain cannot rapidly reduce its mRNA pool, which thus remains large enough to engage a near-preshift number of ribosomes during a prolonged period; as a consequence its ribosomes must work at a reduced rate. The possibility that ppGpp is involved in the control of mRNA production is discussed. After shift-down, the initial part of beta-galactosidase (the auto-alpha fragment) was produced at a higher rate than complete beta-galactosidase in the relaxed strain, as expected when translation is impeded.
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PMID:Control of protein synthesis in Escherichia coli: analysis of an energy source shift-down. 32 60

An endoproteolytic enzyme of Escherichia coli, designated protease III, has been purified about 9,600-fold to homogeneity with a 6% yield. The purified enzyme consists of a single polypeptide chain of Mr 110,000 and is most active at pH 7.4. Protease III is very sensitive to metal-chelating agents and reducing agents. The EDTA-inactivated enzyme can be reactivated by Zn2+, Co2+ or Mn2+. Protease III is devoid of activity toward aminopeptidase, carboxypeptidase, or esterase substrates but rapidly degrades small proteins. When fragments of beta-galactosidase are used as substrates for protease III, the enzyme preferentially degrades proteins with molecular weights of less than 7,000. Protease III cleaves the oxidized insulin B chain at two sites with an initial rapid cleavage at Tyr-Leu (16-17) and a second slower cut at Phe-Tyr (25-26).
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PMID:Purification and characterization of protease III from Escherichia coli. 37 13

Escherichia coli Q13 was infected with bacteriophage Q beta and subjected to energy source shift-down (from glucose-minimal to succinate-minimal medium) 20 min after infection. Production of progeny phage was about fourfold slower in down-shifted cultures than in the cultures in glucose medium. Shift-down did not affect the rate of phage RNA replication, as measured by the rate of incorporation of [14C]uracil in the presence of rifampin, with appropriate correction for the reduced entry of exogenous uracil into the UTP pool. Phage coat protein synthesis was three- to sixfold slower in down-shifted cells than in exponentially growing cells, as determined by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate. The polypeptide chain propagation rate in infected cells was unaffected by the down-shift. Thus, the reduced production of progeny phage in down-shifted cells appears to result from control of phage protein synthesis at the level of initiation of translation. The reduction in the rate of Q beta coat protein synthesis is comparable to the previously described reduction in the rate of synthesis of total E. coli protein and of beta-galactosidase, implying that the mechanism which inhibits translation in down-shifted cells is neither messenger specific nor specific for 5' proximal cistrons. The intracellular ATP pool size was nearly constant after shift-down; general energy depletion is thus not a predominant factor. The GTP pool, by contrast, declined by about 40%. Also, ppGpp did not accumulate in down-shifted, infected cells in the presence of rifampin, indicating that ppGpp is not the primary effector of this translational inhibition.
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PMID:Control of protein synthesis in Escherichia coli: control of bacteriophage Q beta coat protein synthesis after energy source shift-down. 38 18

A gene for somatostatin, a mammalian peptide (14 amino acid residues) hormone, was synthesized by chemical methods. This gene was fused to the Escherichia coli beta-galactosidase gene on the plasmid pBR322. Transformation of E. coli with the chimeric plasmid DNA led to the synthesis of a polypeptide including the sequence of amino acids corresponding to somatostatin. In vitro, active somatostatin was specifically cleaved from the large chimeric protein by treatment with cyanogen bromide. This represents the first synthesis of a functional polypeptide product from a gene of chemically synthesized origin.
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PMID:Expression in Escherichia coli of a chemically synthesized gene for the hormone somatostatin. 41 51

The amino acid sequence of beta-galactosidase (beta-D-galactoside galactohydrolase, EC 3.2.1.23) has been compared to itself and to other proteins. Two segments, each of about 380 amino acids, comprising the first three-fourths of the polypeptide chain, were found to be very similar to each other. It is concluded that they are homologous. The carboxyl-terminal fourth has a high percentage of amino acid identities with dihydrofolate reductase of Escherichia coli, suggesting these sequences also are homologous. A model for the origin of beta-galactosidase is presented. The overall similarity of beta-galactosidase to lac repressor does not appear to be significant.
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PMID:On the evolution of beta-galactosidase. 41 4

1. Potato lectin is a glycoprotein that contains about 47% (by weight) l-arabinose, 3% d-galactose and 11% hydroxyproline. It has a monomeric molecular weight of about 50000 and probably exists as a monomer-dimer system in aqueous solution, with the monomer predominating. It has a very high viscosity, which would indicate either that the molecule is very expanded or that it is an elongated ellipsoid. 2. After prolonged proteolytic digestion of a reduced and carboxymethylated derivative of the lectin, a glycopeptide was isolated (of mol.wt. 32000-34000) that included all the carbohydrate and hydroxyproline of the original glycoprotein but less than 30% of the total original amino acid residues. 3. The arabinose of the glycoprotein is present exclusively as the beta-arabinofuranoside and this includes those residues that are directly linked to the hydroxyproline residues of the polypeptide chain. All the arabinose of the glycoprotein is linked to the polypeptide chain through the hydroxyproline residues; the ratio of arabinose to hydroxyproline is 3.4:1. Although alpha-arabinofuranosides are known to be present in arabinans and arabinogalactans, the natural occurrence of beta-arabinofuranosides has not previously been reported. 4. Nine or ten serine residues of the polypeptide chain are substituted with single alpha-galactopyranoside residues that can be removed by the action of alpha-galactosidase from coffee beans but not by a beta-galactosidase. This is the first report of an alpha-galactoside linkage to serine. The effect of alpha-galactosidase is much greater on a glycopeptide from which the arabinose has been already removed, which indicates a steric hindrance of the galactosidase action by adjacent chains of arabinosides. 5. In 0.5m-NaOH (pH13.7), galactose residues were removed from the serine residues of the glycopeptide by a process of beta-elimination. This reaction took place very slowly in the intact glycopeptide but much more rapidly when the arabinofuranoside residues had been removed. This inhibitory effect of the arabinofuranoside residues on the beta-elimination reaction is likely to be due to a negative charge on the hydroxy groups of the adjacent arabinofuranoside residues, which would be ionized at this high pH value. 6. It is suggested that potato lectin may be representative of a class of soluble plant glycoproteins that would include precursors of the cell-wall glycoprotein extensin. If this is the case, extensin should also contain beta-l-arabinofuranosides linked to hydroxyproline and alpha-d-galactopyranosides linked to serine residues of the polypeptide chain.
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PMID:Properties of potato lectin and the nature of its glycoprotein linkages. 66 30

The molecular genetics of GM1 beta-galactosidase is reviewed. This enzyme exists in two forms, A and B. Form A is monomeric with a molecular weight of 72,000 and appears to be coded by a single autosomal locus. Form B is polymeric and cross-reacts with anti-A antibodies; it is coded wholly or in part by the same locus that codes for A. The simultaneous loss of A and B in GM1 gangliosidosis is explained. None of the other beta-galactosidases, including neutral beta-galactosidase, ceramide lactoside beta-galactosidase or cerebroside beta-galactosidase cross-react with anti-A antibodies, demonstrating that they are coded by loci separate from A. GM1 beta-galactosidase A is heterocatalytic, cleaving beta-D-galactose from ganglioside GM1, lactose, N-acetyllactosamine, and galactose-containing glycoproteins such as asialofetuin, red cell stromal glycoproteins and keratan sulfate. The pleotropic effects of a single mutation affecting the locus for beta-galactosidase A can be explained by a one gene:one polypeptide:many substrates model. Phenotypic variability among beta-galactosidase A mutants may result from better residual activity of the mutant enzyme for one substrate than for another. Patients with normal intelligence and severe bony deformities, who are homozygous for a mutation affecting the enzyme, illustrate this point. Thus far all human mutants for GM1 beta-galactosidase studied are structural mutants, synthesizing nearly normal quantities of mutant enzyme; one is a proven Km mutant, the others are very likely so.
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PMID:Molecular genetics of GM1 beta-galactosidase. 81 20


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