Lipoprotein signal peptidase of Streptococcus suis serotype 2

Abstract

This paper reports the complete coding sequence for a proliprotein signal peptidase (SP-ase) ofStreptococcus suis, Lsp. This is believed to be the first SP-ase described forS. suis. SP-ase II is involved in the removal of the signal peptide from glyceride-modified prolipoproteins. By usingin vitrotranscription/translation systems, it was shown that thelspgene was transcribedin vitro. Functionality of Lsp inEscherichia coliwas demonstrated by using anin vitroglobomycin resistance assay, to show that expression of Lsp inE. coliincreased the globomycin resistance. An isogenic mutant ofS. suisserotype 2 unable to produce Lsp was constructed and shown to process lipoproteins incorrectly, including anS. suishomologue of the pneumococcal PsaA lipoprotein. Five piglets were inoculated with a mixture of both strains in an experimental infection, to determine the virulence of the mutant strain relative to that of the wild-type strain in a competitive challenge experiment. The data showed that both strains were equally virulent, indicating that the knockout mutant oflspis not attenuatedin vivo.