THE TLA-PROTEIN OF PORPHYROMONAS-GINGIVALIS-W50 - A HOMOLOG OF THE RI-PROTEASE PRECURSOR (PRPRI) IS AN OUTER-MEMBRANE RECEPTOR REQUIRED FORGROWTH ON LOW-LEVELS OF HEMIN

The prpR1 gene of Porphyromonas gingivalis W50 encodes the polyprotein precursor (PrpRI) of an extracellular arginine-specific protease, Prp RI is organized into four distinct domains (pro, alpha, beta, and gamm a) and is processed to a heterodimeric protease (RI) which comprises t he alpha and beta components in a noncovalent association, The alpha c omponent contains the protease active site, whereas the beta component appears to have a role in adherence and hemagglutination processes, D NA sequences homologous to the coding region for the RI beta component are present at multiple loci on the P. gingivalis chromosome and may represent a family of related genes, In this report, we describe the c loning, sequence analysis, and characterization of one of these homolo gous loci isolated in plasmid pJM7, The 6,041-bp P. gingivalis DNA fra gment in pJM7 contains a major open eading frame of 3,291 bp with codi ng potential for a protein with an M-r 118,700, An internal region of the deduced sequence (V304 to N768) shows 98% identity to the beta dom ain of PrpRI, and the recombinant product of pJM7 is immunoreactive wi th an antibody specific to the RI beta component, The N terminus of th e deduced sequence has regional similarity to TonB-linked receptors wh ich are frequently involved in periplasmic translocation of hemin, iro n, colicins, or vitamin B-12 in other bacteria, We have therefore desi gnated this gene tla (TonB linked adhesin). In contrast to the parent strain, an isogenic mutant of P. gingivalis W50 in which the tla was i nsertionally inactivated was unable to grow in medium containing low c oncentrations of hemin (<2.5 mg liter(-1)), and hemin-depleted cells o f this mutant failed to respond to hemin in an agar diffusion plate as say, These data suggest a role for this gene product in hemin acquisit ion and utilization, Furthermore, the mutant produced significantly le ss arginine- and lysine-specific protease activities than the parent s train, indicating that there may be a regulatory relationship between tin and other members of this gene family.