Identification of epitopes in Leptospira borgpetersenii leucine-rich repeat proteins

Leptospirosis is considered to be a re-emerging disease that has impacts on public health both globally and in and Thailand. The leptospires outbreak in Thailand during 1999 was largely due to the etiologic agent Leptospira borgpetersenii serogroup Sejroe. This had a related immunity profile in cows from Thailand, which serovars Tarassovi and Sejroe were prevalent. Development of a vaccine protecting against leptospiral infection in livestock has been considered. One family of proteins being targeted as candidates for vaccine development are leucine-rich repeats (LRRs), which have diverse functions such as bacterial host-pathogen interactions, membrane anchoring, invasion and stimulating host defense mechanisms. Identifying leptospiral LRR proteins containing immunogenic epitopes is important for Leptospirosis vaccine development. In this study, we searched LRR genes from L. borgpetersenii serovar Hardjo-bovis strain L550 and LB179 genomic databases in an attempt to find appropriate LRR proteins for vaccine candidates covering the common genospecies detected in Thailand. The in silico analysis, LRR protein secondary and tertiary structures by 3D modeling, and T cell epitope prediction & analysis were performed. In conclusion, we have found seven pairs of conserved LRR genes in L. borpetersenii serovars Hardjo-bovis strains JB197 and L550. Only the LBJ_2271 gene was predicted to be LRR motif subfamily membrane protein with an N-terminal signal sequence, 2 transmembrane domains and an N-glycosylated site. The LRR consensus sequence LXXLXLXXNXL was classified in a typical LRR subfamily. The LBJ_2271 gene sequence has highly homology to genes in other pathogenic Leptospira interrogans serovars; LA_1324, LIC_12401, JX26069, JX26070, JX26071 and JX06072. The LBJ_2271 protein was predicted to containin 14 T cell epitopes, 8 of which are predicted T cell epitopes for Major-Histo-Compatability (MHC) alleles HLA-A(∗)0101, A(∗)0202, A(∗)0203, A(∗)1101, A(∗)3101, A(∗)6802, and HLA-DRB(∗)0401 and DRB(∗)0701, with IC50 values of 0.90-32.28nM, residing outside of the transmembrane domains. At least 5 promising predicted T cell epitopes for alleles HLA-A0202, -A0203, -A1101, -DRB0401 and -DRB0701 had their IC50 lower - equal to IC50 values for the same allele epitopes of known antigenic proteins LigA, LipL32, OMPL1 and LipL36. This study has successfully identified LBJ_2271 as a protein candidate for further study of antigenic immune stimulation for vaccine development.