Leptospiral LruA Is Required for Virulence and Modulates an Interaction with Mammalian Apolipoprotein AI

Abstract

ABSTRACTLeptospirosis is a worldwide zoonosis caused by spirochetes of the genusLeptospira. While understanding of pathogenesis remains limited, the development of mutagenesis inLeptospirahas provided a powerful tool for identifying novel virulence factors. LruA is a lipoprotein that has been implicated in leptospiral uveitis as a target of the immune response. In this study, twolruAmutants, M754 and M765, generated by transposon mutagenesis fromLeptospira interrogansserovar Manilae, were characterized. In M754, the transposon inserted in the middle oflruA, resulting in no detectable expression of LruA. In M765, the transposon inserted toward the 3′ end of the gene, resulting in expression of a truncated protein. LruA was demonstrated to be on the cell surface in M765 and the wild type (WT). M754, but not M765, was attenuated in a hamster model of acute infection. A search for differential binding to human serum proteins identified a serum protein of around 30 kDa bound to the wild type and the LruA deletion mutant (M754), but not to the LruA truncation mutant (M765). Two-dimensional separation of proteins from leptospiral cells incubated with guinea pig serum identified the 28-kDa apolipoprotein A-I (ApoA-I) as a major mammalian serum protein that bindsLeptospirain vitro. Interestingly, M754 (with no detectable LruA) bound more ApoA-I than did the LruA-expressing strains Manilae wild type and M765. Our data thus identify LruA as a surface-exposed leptospiral virulence factor that contributes to leptospiral pathogenesis, possibly by modulating cellular interactions with serum protein ApoA-I.