Leptospiral outer membrane protein LipL41 is not essential for acute leptospirosis but requires a small chaperone protein, lep, for stable expression

Leptospirosis is a worldwide zoonosis caused by pathogenic Leptospira spp., but knowledge of leptospiral pathogenesis remains limited. However, the development of mutagenesis systems has allowed the investigation of putative virulence factors and their involvement in leptospirosis. LipL41 is the third most abundant lipoprotein found in the outer membrane of pathogenic leptospires and has been considered a putative virulence factor. LipL41 is encoded on the large chromosome 28 bp upstream of a small open reading frame encoding a hypothetical protein of unknown function. This gene was named lep for LipL41 expression partner. In this study lipL41 was found to be co-transcribed with lep. Two transposon mutants were characterized: a lipL41 mutant and a lep mutant. In the lep mutant LipL41 protein levels were reduced by approximately 90 . Lep was shown through cross-linking and co-expression experiments to bind to LipL41. Lep is proposed to be a molecular chaperone essential for stable expression of LipL41. The role of LipL41 and Lep in the pathogenesis of L. interrogans was investigated; surprisingly neither of these two unique proteins was essential for acute leptospirosis.