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

The nucleotide sequence of the gene encoding the cytoplasmic N,N'-diacetylc hitobiase [EC 3.2.1.14] from Vibrio parahaemolyticus (ATCC #27969) has been determined, The deduced peptide sequence of this unusual P-hexosaminidase surprisingly shows minimum evolutionary relationship to two other reported N,N'-diacetylchitobiases from vibrios, except in highly conserved regions w hich are also homologous to lysosomal P-hexosaminidases from eukaryotes inc luding humans. In contrast, the two other P-hexosaminidases from vibrios wi th reported sequences are much more closely related to each other. This nov el 85 kDa cytoplasmic glycosyl hydrolase with restricted specificity partic ipates 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 metab olism of N,N'-diacetylchitobiose .These pathways use chitin-binding protein s for the adherence of the bacterial chitinase to the substrate, and an ext racellular chitinase and a periplasmic chitodextrinase to produce N,N'-diac etylchitobiose, The Tr, parahaemolyticus cytoplasmic N,N,N'-diacetyl-chitob iase reported herein appears to be a unique protein, lacking a signal seque nce, and genetically distant from other known chitinoclastic beta-N,N'-diac etyl-hexosaminidases. This is consistent with its limited substrate specifi city to small GlcNAc terminated oligosaccharides and its cytoplasmic rather than periplasmic localization.