HEMOGLOBIN RECEPTOR PROTEIN IS INTRAGENICALLY ENCODED BY THE CYSTEINEPROTEINASE-ENCODING GENES AND THE HEMAGGLUTININ-ENCODING GENE OF PORPHYROMONAS-GINGIVALIS

The obligately anaerobic bacterium Porphyromonas gingivalis produces c haracteristic black-pigmented colonies on blood agar. It is thought th at the black pigmentation is caused by haem accumulation and is relate d to virulence of the microorganism. P. gingivalis cells expressed a p rominent 19 kDa protein when grown on blood agar plates. Analysis of i ts N-terminal amino acid sequence indicated that the 19 kDa protein wa s encoded by an internal region (HGP15 domain) of an arginine-specific cysteine proteinase (Arg-gingipain, RGP)-encoding gene (rgp1) and was also present in genes for lysine-specific cysteine proteinases (prtP and kgp) and a haemagglutinin (hagA) of P. gingivalis. The HGP15 domai n protein was purified from an HGP15-overproducing Escherichia coli an d was found to have the ability to bind to haemoglobin in a pH-depende nt manner. The anti-HGP15 antiserum reacted with the 19 kDa haemoglobi n-binding protein in the envelope of P. gingivalis. P. gingivalis wild -type strain showed pH-dependent haemoglobin adsorption, whereas its n on-pigmented mutants that produced no HGP15-related proteins showed de ficiency in haemoglobin adsorption. These results strongly indicate a close relationship among HGP15 production, haemoglobin adsorption and haem accumulation of P. gingivalis.