Structure of the beta-glucosidase gene bglA of Clostridium thermocellum. Sequence analysis reveals a superfamily of cellulases and beta-glycosidases including human lactase/phlorizin hydrolase.
The nucleotide sequence of the Clostridium thermocellum gene bglA, coding for the thermostable beta-glucosidase A, has been determined. The coding region of 1344 bp was identified by comparison with the N-terminal amino acid squence of recombinant beta-glucosidase A purified from Escherichia coli. The deduced amino acid sequence corresponds to a protein of 51,482 Da. The coding region is flanked by putative promoter and transcription terminator sequences. The protein is unrelated to beta-glucosidase B of C. thermocellum, but has a high level of similarity with other bacterial beta-glucosidases and phospho-beta-glucosidases. Similarity is also observed with the beta-galactosidase of the archaebacterium Sulfolobus solfataricus. Unexpectedly, it was found that human lactase-phlorizin hydrolase contains three copies of a sequence closely related to C. thermocellum beta-glucosidase A (up to 40% sequence identity). These diverse beta-glucosidases can therefore be grouped into an enzyme family (BGA) of common structural design. Sequence comparison by hydrophobic cluster analysis revealed that all BGA enzymes share a well conserved region which is homologous to the catalytic domain of the widely distributed cellulase family A. A distinctive feature of this domain is the sequence motif His-Asn-Glu-Pro in which the catalytic residues His and Glu are separated by 35-55 amino acid residues. The cellulase family A and the beta-glucosidase family BGA might thus be considered as members of a protein super-family comprising beta-glucanases and beta-glycosidases from all three primary kingdoms of living organisms.
Gräbnitz
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Institute for Microbiology, Technical University Munich, Federal Republic of Germany.
Seiss
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Rücknagel
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Staudenbauer
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WL
D000595:Amino Acid Sequence; D001483:Base Sequence; D002480:Cellulase / Q000235:genetics*; D003013:Clostridium / Q000235:genetics*; D004591:Electrophoresis, Polyacrylamide Gel; D005798:Genes, Bacterial; D006801:Humans; D043322:Lactase; D010694:Lactase-Phlorizin Hydrolase / Q000235:genetics*; D008969:Molecular Sequence Data; D005810:Multigene Family; D011401:Promoter Regions, Genetic; D015183:Restriction Mapping; D016415:Sequence Alignment; D012689:Sequence Homology, Nucleic Acid; D014158:Transcription, Genetic; D001616:beta-Galactosidase / Q000235:genetics*; D001617:beta-Glucosidase / Q000235:genetics*
D043322:Lactase; D001617:beta-Glucosidase; D001616:beta-Galactosidase; D002480:Cellulase; D010694:Lactase-Phlorizin Hydrolase