Analysis of the prtP gene encoding porphypain, a cysteine proteinase of Porphyromonas gingivalis

The cloning and sequencing of the gene encoding porphypain, a cysteine proteinase previously isolated from detergent extracts of the Porphyromonas gingivalis W12 cell surface, are described. The prtP gene encoded a unique protein of 1,732 amino acids, including a putative signal sequence for protein secretion. The predicted molecular mass for the mature protein was 186 kDa, which was close to the observed molecular mass of 180 kDa. There was one copy of prtP in the genomes of seven P. gingivalis strains examined. The gene,vas located 5' to a region with a high degree of homology to the insertion element IS1126 in P. gingivalis W12. The PrtP protein had regions of high homology to HagA, a hemagglutinin of P. gingivalis, and to several purported proteinases of P. gingivalis that have Arg-X specificity. A detailed comparison of genes encoding the latter and cpgR suggested that rgp-1, prpR1, prtR, agp, cpgR, and possibly prtH were derived from identical genetic loci. Although an rgp-1-like locus was detected in seven P.gingivalis strains by Southern blot analyses, agp and cpgR were not detected, not even in the strains from which they were originally isolated. In addition, at least 20 copies of a repeat region common to PrtP, the Rgp-1-like proteins, and HagA were observed in each of the seven genomes examined. The repeat region hybridization patterns for strains W83 and W50 were very similar, and they were identical for strains 381 and ATCC 33277, providing further evidence that these strains are closely related genetically.