N,N'-diacetylchitobiase of Vibrio harveyi. Primary structure, processing, and evolutionary relationships

The nucleotide sequence of the gene, chb, encoding the outer membrane protein, N,N'-diacetylchitobiase (chitobiase), of the marine bacterium, Vibrio harveyi, has been determined. The amino acid sequence of prechitobiase was derived from the nucleotide sequence. Prechitobiase has a molecular mass of 97,771 Da and consists of 883 amino acid residues. A characteristic signal peptide is present at the amino terminus whose removal is inhibited by the antibiotic, globomycin, suggesting that mature chitobiase is a lipoprotein with a maturation pathway similar to that of the Escherichia coli major outer membrane lipoprotein. A perfect homology to six amino acids at the processing and modification region of the outer membrane lipoprotein of E. coli was found with amino acids 15-19 of the deduced prechitobiase protein sequence. Chitobiase shares similarities and possibly common ancestry with the alpha-chain of the human beta-hexosaminidase. A comparison of the amino acid sequences of chitobiase and the alpha-chain of beta-hexosaminidase gave a highly significant alignment score of 19.1 standard deviation units above a mean randomized alignment score. Primer extension analysis of the promoter region revealed three transcription initiation sites used by E. coli cells harboring the chb gene, two of which were also evident in V. harveyi cells.