The adherence-associated lipoprotein P100, encoded by an opp operon structure, functions as the oligopeptide-binding domain OppA of a putative oligopeptide transport system in Mycoplasma hominis

Mycoplasma hominis, a cell-wail-less prokaryote,was shown to be cytoadheren t by the participation of a 100-kDa membrane protein (P100), To identify th e gene encoding P100, peptides of P100 were partially sequenced to enable t he synthesis of P100-specific oligonucleotides suitable as probes for the d etection of the P100 gene. With this strategy, we identified a genomic regi on of about 10.4 kb in M, hominis PEG carrying the P100 gene. Analysis of t he complete deduced protein sequence suggests that P100 is expressed as a p relipoprotein with a structure in the N-terminal region common to peptide-b inding proteins and an ATP- or GTP-binding P-loop structure in the C-termin al region. Downstream of the P100 gene, an additional four open reading fra mes putatively encoding the four core domains of an active transport system , OppBCDF, were localized. The organization of the P100 gene and oppBCDF; i n a transcriptionally active operon structure was demonstrated in Northern blot and reverse transcription-PCR analyses, as all gene-specific probes de tected a common RNA of 9.5 kb. Primer extension analysis revealed that the transcriptional initiation site was localized 323 nucleotides upstream of t he methionine-encoding ATG of the P100 gene. The peptide-binding character of the P100 protein aas confirmed by fluorescence spectroscopy and strongly suggests that the cytoadherence-mediating lipoprotein P100 represents OppA , the substrate-binding domain of a peptide transport system in M, hominis.