In Silico Vaccine Designing Targeting the Virulence Factors of mce Operons of Mycobacterium avium subsp. Paratuberculosis

Background: Mycobacterium avium sp. paratuberculosis (MAP) causes Paratuberculosis (pTB) in domestic livestock and has also been associated with auto-immune disorders in humans. Infection leads to huge economic losses to the farmers associated with livestock production system worldwide. Currently, search to find proteins with potential to develop as vaccine candidates against MAP are underway. Objective: In this study, we aimed to explore the immunogenicity of the proteins of mammalian cell entry (mce) operons of MAP using computational tools. Method: Genes of mce operons of MAP strain K10 were selected and their orthologs identification was done using VFanalyzer tool. Mce proteins encoded by these operons were analyzed for their antigenicity and sub-cellular localization. Three dimensional structures for Mce proteins were predicted using Phyre2. B cell and T cell epitope analysis was done using methods available at Immune Epitope Database and Analysis Resource. Selection analysis of mce genes was also done. Results: Eight Mce proteins were predicted with B cell and T cell epitopes. Some of them were reported with overlapping B cell and T cell epitopes. We found positively selected sites within some predicted epitopes that indicated some kind of selection pressure by immune system on these protein regions. Some predicted epitopes also had similarity with experimentally identified epitopes of Mce proteins of M. tuberculosis which further strengthened the immunogenic role of Mce proteins. Conclusion: Our findings may potentially assist in the development of effective vaccine against the incurable infection due to MAP bacilli in the domestic livestock species.

Analysis of Expression Profile of Mammalian Cell Entry (mce) Operons of Mycobacterium tuberculosis

ABSTRACT The sequencing of the complete genome of M. tuberculosis H37Rv has resulted in the recognition of four mce operons in its genome by in silico analysis. In an attempt to understand the significance of the redundancy of mce operons, we analyzed the expression profile of mce operons after different periods of growth in culture as well as during in vivo infection. Our results strongly suggest that mce1 is expressed as a polycistronic message. In culture from day 8 to day 12, expression of only mce1 was observed, but as the cultures progress towards stationary phase the expression profile of mce operons was altered; the transcripts of the mce1 operon were barely detected while those of the mce4 operon were prominent. In an analysis of the expression of mce operons in tubercle material collected from infected animal tissues, we detected the expression of mce1, -3 and -4. Our results imply that mce operons other than mce1 are also expressed during infection and that it is necessary to examine their role in pathogenesis.