Genetic analyses of the single-pass transmembrane protein TspA in Neisseria meningitidis

Neisseria meningitidis typically colonizes human nasopharynges and happens to invade the bloodstream and cerebrospinal fluid. While the machinery on meningococcal pathogenesis via the pili have been uncovered in detail, molecular characters and mechanisms by pathogenic factors other than pili has been remained to be elucidated. In this study, one of the factors, outer membrane protein TspA, was examined. Biochemical and immunological analyses revealed that TspA was a single-pass transmembrane protein protruding the N-terminus extracellularly at the outer membrane. Infection assays of tspA deletion (ΔtspA) mutant and the ΔtspA mutant ectopically complemented with the tspA+ gene with human brain microvascular endothelial cells (HBMEC) revealed that tspA was participated in the meningococcal adhesion and invasion. Since tspA mutation is reported to be unlink to the pili, TspA was considered to function directly to HBMEC. However, tspA mutant deleted with the N-terminal extracellular domains, chimeric tspA mutants in which the N-terminal domain fused to the Escherichia coli periplasmic proteins MalE and EmrA or dimeric proteins DsbG and DsbC did not compensate the infection ability to HBMEC. The results in this study might implicate some insights into meningococcal infection to human cells in a pili-indirect manner.