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)

In streptococci, HPr, a phosphocarrier of the phosphoenolpyruvate:sugar phosphotransferase transport system (PTS), undergoes multiple posttranslational chemical modifications resulting in the formation of HPr(His approximately P), HPr(Ser-P), and HPr(Ser-P)(His approximately P), whose cellular concentrations vary with growth conditions. Distinct physiological functions are associated with specific forms of HPr. We do not know, however, the cellular thresholds below which these forms become unable to fulfill their functions and to what extent modifications in the cellular concentrations of the different forms of HPr modify cellular physiology. In this study, we present a glimpse of the diversity of Streptococcus salivarius ptsH mutants that can be isolated by positive selection on a solid medium containing 2-deoxyglucose and galactose and identify 13 amino acids that are essential for HPr to properly accomplish its physiological functions. We also report the characterization of two S. salivarius mutants that produced approximately two- and threefoldless HPr and enzyme I (EI) respectively. The data indicated that (i) a reduction in the synthesis of HPr due to a mutation in the Shine-Dalgarno sequence of ptsH reduced ptsI expression; (ii) a threefold reduction in EI and HPr cellular levels did not affect PTS transport capacity; (iii) a twofold reduction in HPr synthesis was sufficient to reduce the rate at which cells metabolized PTS sugars, increase generation times on PTS sugars and to a lesser extent on non-PTS sugars, and impede the exclusion of non-PTS sugars by PTS sugars; (iv) a threefold reduction in HPr synthesis caused a strong derepression of the genes coding for alpha-galactosidase, beta-galactosidase, and galactokinase when the cells were grown at the expense of a PTS sugar but did not affect the synthesis of alpha-galactosidase when cells were grown at the expense of lactose, a noninducing non-PTS sugar; and (v) no correlation was found between the magnitude of enzyme derepression and the cellular levels of HPr(Ser-P).
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PMID:Diversity of Streptococcus salivarius ptsH mutants that can be isolated in the presence of 2-deoxyglucose and galactose and characterization of two mutants synthesizing reduced levels of HPr, a phosphocarrier of the phosphoenolpyruvate:sugar phosphotransferase system. 1148 68

Streptococcus salivarius is a lactose- and galactose-positive bacterium that is phylogenetically closely related to Streptococcus thermophilus, a bacterium that metabolizes lactose but not galactose. In this paper, we report a comparative characterization of the S. salivarius and S. thermophilus gal-lac gene clusters. The clusters have the same organization with the order galR (codes for a transcriptional regulator and is transcribed in the opposite direction), galK (galactokinase), galT (galactose-1-P uridylyltransferase), galE (UDP-glucose 4-epimerase), galM (galactose mutarotase), lacS (lactose transporter), and lacZ (beta-galactosidase). An analysis of the nucleotide sequence as well as Northern blotting and primer extension experiments revealed the presence of four promoters located upstream from galR, the gal operon, galM, and the lac operon of S. salivarius. Putative promoters with virtually identical nucleotide sequences were found at the same positions in the S. thermophilus gal-lac gene cluster. An additional putative internal promoter at the 3' end of galT was found in S. thermophilus but not in S. salivarius. The results clearly indicated that the gal-lac gene cluster was efficiently transcribed in both species. The Shine-Dalgarno sequences of galT and galE were identical in both species, whereas the ribosome binding site of S. thermophilus galK differed from that of S. salivarius by two nucleotides, suggesting that the S. thermophilus galK gene might be poorly translated. This was confirmed by measurements of enzyme activities.
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PMID:Galactose and lactose genes from the galactose-positive bacterium Streptococcus salivarius and the phylogenetically related galactose-negative bacterium Streptococcus thermophilus: organization, sequence, transcription, and activity of the gal gene products. 1179 Jul 49

The genetic determinants for lactose utilization from Lactobacillus delbrueckii subsp. bulgaricus ATCC 11842 and galactose utilization from Lactococcus lactis subsp. cremoris MG 1363 were heterologously expressed in the lysine-overproducing strain Corynebacterium glutamicum ATCC 21253. The C. glutamicum strains expressing the lactose permease and beta-galactosidase genes of L. delbrueckii subsp. bulgaricus exhibited beta-galactosidase activity in excess of 1000 Miller units/ml of cells and were able to grow in medium in which lactose was the sole carbon source. Similarly, C. glutamicum strains containing the lactococcal aldose-1-epimerase, galactokinase, UDP-glucose-1-P-uridylyltransferase, and UDP-galactose-4-epimerase genes in association with the lactose permease and beta-galactosidase genes exhibited beta-galactosidase levels in excess of 730 Miller units/ml of cells and were able to grow in medium in which galactose was the sole carbon source. When grown in whey-based medium, the engineered C. glutamicum strain produced lysine at concentrations of up to 2 mg/ml, which represented a 10-fold increase over the results obtained with the lactose- and galactose-negative control, C. glutamicum 21253. Despite their increased catabolic flexibility, however, the modified corynebacteria exhibited slower growth rates and plasmid instability.
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PMID:Heterologous expression of lactose- and galactose-utilizing pathways from lactic acid bacteria in Corynebacterium glutamicum for production of lysine in whey. 1512 44

Carbon catabolite repression by the CreA-transcriptional repressor is widespread in filamentous fungi, but the mechanism by which glucose triggers carbon catabolite repression is still poorly understood. We investigated the hypothesis that the growth rate on glucose may control CreA-dependent carbon catabolite repression by using glucose-limited chemostat cultures and the intracellular beta-galactosidase activity of Aspergillus nidulans, which is repressed by glucose, as a model system. Chemostat cultures at four different dilution rates (D = 0.095, 0.068, 0.045 and 0.015 h-1) showed that formation of beta-galactosidase activity is repressed at the two highest Ds, but increasingly derepressed at the lower Ds, the activity at 0.015 h-1 equalling that in derepressed batch cultures. Chemostat cultures with the carbon catabolite derepressed A. nidulans mutant strain creADelta4 revealed a dilution-rate independent constant beta-galactosidase activity of the same range as that found in the wild-type strain at D = 0.015 h-1. Two other enzymes--isocitrate lyase, which is almost absent on glucose due to a CreA-independent mechanism; and galactokinase, which is formed constitutively and independent of CreA--were measured as controls. They were formed at constant activity at each dilution rate, both in the wild-type strain as well as in the carbon catabolite derepressed mutant strain. We conclude that the growth rate on glucose is a determinant of carbon catabolite repression in A. nidulans, and that below a certain growth rate carbon catabolite derepression occurs.
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PMID:CreA-mediated carbon catabolite repression of beta-galactosidase formation in Aspergillus nidulans is growth rate dependent. 1515 74

A chromosomal DNA fragment of 7.8 kb from Lactobacillus coryniformis CECT 5711 was cloned in Escherichia coli K-12 and was found to express a functional beta-galactosidase. Nucleotide sequence analysis showed that this fragment contained two partially overlapping genes, the lacL (1,881 bp) and the lacM (960 bp), that encode the subunits of a heterodimeric beta-galactosidase, with estimated molecular masses of 72,129 and 35,233 Da, respectively. Other three incomplete open reading frames showing homology to another beta-galactosidase, an alpha-galactosidase, and a galactokinase, respectively, were also found. The L. coryniformis beta-galactosidase was overproduced in E. coli by using an isopropyl-beta-D: -thiogalactopyranoside (IPTG) expression system. Two new proteins with an estimated M (r) s of approximately 72,000 and 35,000 appeared upon induction with IPTG, and extracts of the recombinant E. coli strain showed beta-galactosidase activity.
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PMID:Cloning and characterization of a beta-galactosidase encoding region in Lactobacillus coryniformis CECT 5711. 1682 Sep 50

The ability of Hypocrea jecorina (Trichoderma reesei) to grow on lactose strongly depends on the formation of an extracellular glycoside hydrolase (GH) family 35 beta-galactosidase, encoded by the bga1 gene. Previous studies, using batch or transfer cultures of pregrown cells, had shown that bga1 is induced by lactose and d-galactose, but to a lesser extent by galactitol. To test whether the induction level is influenced by the different growth rates attainable on these carbon sources, bga1 expression was compared in carbon-limited chemostat cultivations at defined dilution (=specific growth) rates. The data showed that bga1 expression by lactose, d-galactose and galactitol positively correlated with the dilution rate, and that galactitol and d-galactose induced the highest activities of beta-galactosidase at comparable growth rates. To know more about the actual inducer for beta-galactosidase formation, its expression in H. jecorina strains impaired in the first steps of the two d-galactose-degrading pathways was compared. Induction by d-galactose and galactitol was still found in strains deleted in the galactokinase-encoding gene gal1, which is responsible for the first step of the Leloir pathway of d-galactose catabolism. However, in a strain deleted in the aldose/d-xylose reductase gene xyl1, which performs the reduction of d-galactose to galactitol in a recently identified second pathway, induction by d-galactose, but not by galactitol, was impaired. On the other hand, induction by d-galactose and galactitol was not affected in an l-arabinitol 4-dehydrogenase (lad1)-deleted strain which is impaired in the subsequent step of galactitol degradation. These results indicate that galactitol is the actual inducer of Bga1 formation during growth on d-galactose in H. jecorina.
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PMID:Induction of extracellular beta-galactosidase (Bga1) formation by D-galactose in Hypocrea jecorina is mediated by galactitol. 1725 22

In this study, we analyze the expression of the Aspergillus nidulans bgaD-lacpA gene couple (encoding an intracellular beta-galactosidase and a lactose permease) in the presence of D-galactose. This monosaccharide can be catabolized via alternative, independent pathways in this model organism. The inductive capabilities of intermediates of the two alternative routes of D-galactose utilization were addressed in loss-of-function mutants defective in a defined step in one of the two pathways. In a galactokinase (galE9) mutant, the cluster is strongly induced by D-galactose, suggesting that formation of Leloir pathway intermediates is not required. The expression profiles of bgaD and lacpA were similar in wild type, L-arabinitol dehydrogenase (araA1), and hexokinase (hxkA1) negative backgrounds, indicating that intermediates of the oxido-reductive pathway downstream of galactitol are not necessary either. Furthermore, bgaD-lacpA transcription was not induced in any of the tested strains when galactitol was provided as the growth substrate. An hxkA1/galE9 double mutant cannot grow on d-galactose at all, but still produced bgaD and lacpA transcripts upon transfer to d-galactose. We therefore concluded that the physiological inducer of the bgaD-lacpA gene cluster upon growth on D-galactose is the nonmetabolized sugar itself.
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PMID:Metabolism of D-galactose is dispensable for the induction of the beta-galactosidase (bgaD) and lactose permease (lacpA) genes in Aspergillus nidulans. 2514 6


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