System specificity of the TpsB transporters of coexpressed two-partner secretion systems of Neisseria meningitidis

Abstract

The two-partner secretion (TPS) systems of Gram-negative bacteria consist of a largesecreted exoprotein (TpsA) and a transporter protein (TpsB) located in the outer membrane. TpsA targets TpsB for transport across the membrane via its ~30-kDa TPS domain locatedat its N terminus, and this domain is also the minimal secretory unit. Neisseria meningitidis genomes encode up to five TpsAs and two TpsBs. Sequence alignments of TPS domains suggested that these are organized into three systems, while there are two TpsBs, which raised questions on their system specificity. We show here that the TpsB2 transporter of Neisseria meningitidis is able to secrete all types of TPS domains encoded in N. meningitidisand the related species Neisseria lactamica but not domains of Haemophilus influenzae andPseudomonas aeruginosa. In contrast, the TpsB1 transporter seemed to be specific for its cognate N. meningitidis system and did not secrete the TPS domains of other meningococcalsystems. However, TpsB1 did secrete the TPS2b domain of N. lactamica, which is related tothe meningococcal TPS2 domains. Apparently, the secretion depends on specific sequences within the TPS domain rather than the overall TPS domain structure. © 2013, American Society for Microbiology.