Sequence analysis of the beta-N-acetylhexosaminidase gene of Vibrio vulnificus: evidence for a common evolutionary origin of hexosaminidases.

DNA cloned from the marine bacterium Vibrio vulnificus into Escherichia coli HB101 can hydrolyze chitin oligomer analogs in the recipient. The nucleotide sequence of the cloned DNA was determined and a single long open reading frame of 2541 base pairs (initiation codon through termination codon) was found. The nucleotide sequence predicts a gene product of 847 amino acids and a molecular mass of 94.3 kDa. In vitro transcription and translation analyses indicated a single protein of 94 kDa encoded by the cloned DNA. The gene product hydrolyzes methylumbelliferyl beta-D conjugates of chitotriose, chitobiose, N-acetylglucosamine, and N-acetylgalactosamine and has, therefore, been termed a beta-N-acetylhexosaminidase. The predicted protein shares a high degree of sequence similarity with the chitobiase of Vibrio harveyi and limited similarity with the alpha chain of human beta-hexosaminidase. Cluster analyses suggest a common evolutionary ancestor for all known hexosaminidase enzymes, with no detectable relationship to known chitinases.