Comparative subproteome analysis of three representative Leptospira interrogans vaccine strains reveals cross-reactive antigens and novel virulence determinants.

Unlabelled: Pathogenic Leptospira spp. causes leptospirosis in China and throughout the world. Here, we have sequenced two L. interrogans moderately virulent vaccine strains JDL03 (serovar Canicola) and JDL10 (serovar Hebdomadis) used in China. We selected a subproteomic approach to identify surface-exposed proteins including OMPs and extracellular proteins of these two strains plus a highly virulent vaccine strain 56601 (serovar Lai). Comparative surface-exposed proteome among the three strains indicated 81 cores, 61 dispensable and 122 unique surface-exposed proteins. Finally, the 10 highly conserved surface-exposed or subsurface proteins included two known cross-reactive antigens (LipL32 and LA_3469) and another two novel antigens (LA_0136 and LA_0505) displaying conserved immunoreactivity among 15 Chinese epidemic serovars. Furthermore, many potential virulence factors were detected in these identified surface-exposed proteins, such as Loa22, LipL32, LenC, LenF and OmpL37. Interestingly, LipL45, ClpA and ClpB, exhibiting obvious amino acid mutations among str.56601, str.JDL03 and JDL10, might contribute to virulence differences observed among these strains. Additionally, specific surface-exposed proteins in virulent str.56601 were considered to be key virulence determinants, such as Zn-dependent protease, cholesterol oxidase precursor, and so on. In all, we had relatively complete surface-exposed subproteomes of L. interrogans, which will enhance our understanding of leptospiral pathogenesis and key virulence determinants.

Biological Significance: The present work demonstrates the use of genomic sequencing and subproteomic studies for the identification of potential vaccine and diagnostic antigen candidates against leptospirosis. The data show the conserved surface-exposed proteins to be novel potentially vaccine/diagnostic candidates. Furthermore, the data also show that LipL45, ClpA, ClpB and a lipoprotein from these three strains plus another highly virulent strain Fiocruz L1-130 contain specific amino acid mutations in strains JDL03 and JDL10. The surface-exposed subproteome of pathogenic L. interrogans could provide valuable information to gain a more complete understanding of leptospiral pathogenesis and virulence determinants.