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Cloning and expression in Escherichia eoli of the nahA gene from Porphyromonas gingivalis

Department of Microbiology and Immunology, Medical Sciences Building, P.O. Box 138, University of Leicester, University Road, Leicester LE1 9HN, UK Porphyromonas gingivalis has been imp1 icated in human periodontal diseases. It expresses a number of exoglycosidase enzymes capable of hydrolysing host proteoglycan residues. As a first stage to explore the role of these enzymes in periodontal tissue damage, the nahA gene of P. gingivalis W83, which encodes /?-N-acetylhexosaminidase (P-Nahase), was cloned. The gene was expressed poorly in Escherichia coli, but increased expression was achieved by cloning the nahA gene downstream of the tac promoter. Southern blot analysis revealed that nahA was present as a single copy, and it was found in all the other P. gingivalis strains tested. In contrast, sequences homologous to nahA were not detected in either P. endodontalis or P. asaccharolytica. The nahA gene was 2331 bp long and encoded a /?-Nahase enzyme of 777 amino acids with a predicted molecular mass of 87 kDa. A characteristic signal peptide for an acylated lipoprotein was present a t the amino-terminus, suggesting that the mature /?-Nahase is a lipoprotein. The predicted amino acid sequence of the P. gingivalis /?-Nahase shared homology with the catalytic domains of the human /?-Nahase enzyme and the chitinase of Vibrio harveyi, suggesting a common catalytic mechanism.