Sequence of the V. parahaemolyticus gene for cytoplasmic N,N'-diacetylchitobiase and homology with related enzymes

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The nucleotide sequence of the gene encoding the cytoplasmic N,N'-diacetylchitobiase [EC] from Vibrio parahaemolyticus (ATCC 27969) has been determined. The deduced peptide sequence of this unusual β-hexosaminidase surprisingly shows minimum evolutionary relationship to two other reported N,N'-diacetylchitobiases from vibrios, except in highly conserved regions which are also homologous to lysosomal β-hexosaminidases from eukaryotes including humans. In contrast, the two other β-hexosaminidases from vibrios with reported sequences are much more closely related to each other. This novel 85 kDa cytoplasmic glycosyl hydrolase with restricted specificity participates in the high level utilization of chitin-derived 2-deoxy-2-acetamido-D-glucose (GlcNAc) by vibrios as one of two parallel pathways for the metabolism of N,N'-diacetylchitobiose. These pathways use chitin-binding proteins for the adherence of the bacterial chitinase to the substrate, and an extracellular chitinase and a periplasmic chitodextrinase to produce N,N'-diacetylchitobiose. The V. parahaemolyticus cytoplasmic N,N'-diacetyl-chitobiase reported herein appears to be a unique protein, lacking a signal sequence, and genetically distant from other known chitinoclastic β-N,N'-diacetyl-hexosaminidases. This is consistent with its limited substrate specificity to small GlcNAc terminated oligosaccharides and its cytoplasmic rather than periplasmic localization.

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Journal of Biochemistry

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