Role of ribosomal protein L12 in gonococcal invasion of Hec1B cells

Previous studies led to the development of a model of contact-induced enhan ced gonococcal invasion of human reproductive cells that utilizes the lutro pin receptor (LHr) as both the induction signal for conversion to this enha nced-gonococcal-invasion phenotype (Inv(+) GC) and as the specific Inv(+) G C uptake mechanism. This model proposes that gonococci express a surface fe ature that mimics human chorionic gonadotropin (hCG), the cognate ligand fo r LHr, and that this structure is responsible for the specific and producti ve interaction of GC with LHr. In this report, we identify a 13-kDa gonococ cal protein with immunological similarities to hCG. The antiserum reactivit y is specific since interaction with the 13-kDa gonococcal protein can be b locked by the addition of highly purified hCG, This gonococcal "hCG-like" p rotein, purified from two-dimensional gets and by immunoprecipitation, was determined by N-terminal sequencing to be the ribosomal protein LL2. We pre sent evidence that gonococcal L12 is membrane associated and surface expose d in gonococci, as shown by immunoblot analysis of soluble and insoluble go nococcal protein and antibody adsorption studies with fixed GC. Using highl y purified recombinant gonococcal L12, we show that preincubation of Inv(-) GC with micromolar amounts of rL12 leads to a subsequent five- to eightfol d increase in invasion of the human endometrial cell line, Hec1B. In additi on, nanomolar concentrations of exogenous L12 inhibits gonococcal invasion to approximately 70% of the level in controls. Thus, we propose a novel cel lular location for the gonococcal ribosomal protein L12 and concomitant fun ction in LHr-mediated gonococcal invasion of human reproductive cells.