The 19 kDa Protein from ＂Mycobacterium Avium Subspecies Paratuberculosis＂ is a Glycolipoprotein

This study characterizes the 19 kDa protein expressed by Mycobacterium avium subspecies paratuberculosis (MAP) as a glycolipoprotein, providing the foundation for future experiments regarding its antigenicity and role in disease pathogenicity. We have previously shown that a 4.8 kb insert from MAP will produce a 16 kDa recombinant protein when expressed in Escherichia coli and 19 kDa recombinant protein when expressed in M. smegmatis (smeg19K). The difference of 3 kDa in size of these expressed proteins may be related to post translational modifications that occur in Mycobacterium species. We hypothesized that smeg19K is a glycolipoprotein since BLAST analysis revealed approximately 76% amino acid identity between the MAP 19 kDa protein and a known lipoglycoprotein, the 19 kDa protein of M. tuberculosis. This prediction was confirmed by the following positive staining of smeg19K with Sudan Black 4B, a postelectrophoresis dye used to stain for lipids. Smeg19K has also stained positively for glycosylation with the lectin concavalin A, a highly specific stain for mannose residues. As expected, treatment with tunicamycin (an antibiotic known to inhibit N-glycosylation) and treatment with deglycosylation assay (non-specific for mannose), showed no reduction in size of 19 kDa glycolipoprotein.