Mycobacterium paratuberculosis, Mycobacterium smegmatis, posttranslational modification, Crohn s disease


Despite the fact that E. coli supports limited posttranslational modification, this bacterium has been universally used as the expression system of choice. Expression of modified proteins in E. coli may lead to expression of recombinant proteins that lack essential immunomodulatory or catalytic components essentials for infectious processes. Previously in our laboratory, pMptb#28 plasmid containing a 4.8 kb insert from M. paratuberculosis has been identified which expressed 16 kDa recombinant protein in E. coli and 19 kDa recombinant protein in Mycobacterium smegmatis. The objective of this study is to identify the ORF sequence, investigate possible posttranslational modification and characterize the protein forms in the two hosts. Earlier in the study, the genome sequence for M. paratuberculosis was not available and therefore sequencing both the 5' and 3' ends of the 4.8 kb insert did not help in the identification of the ORF. However, unidirectional Exonuclease deletion resulted in identification of subclones containing possible ORF sequence. Later on, the publication of the M. paratuberculosis genome sequence along with BLAST analysis of sequences from the subclones resulted in the identification of 486 bp ORF with significant identity to that from M. tuberculosis and M. leprae. Cloning of the 486 ORF coding sequence in E. coli resulted in the expression of 16 kDa protein similar to the calculated predicted size of translated peptide. Cloning of the 486 bp ORF coding sequence in M. smegmatis resulted in the expression of 19 kDa protein similar to that from M. paratuberculosis. The 16/19 kDa forms of the same protein were verified using rabbit anti-M. paratuberculosis antibodies adsorbed in E. coli and M. smegmatis lysates. The size of the 19 kDa proteins was not reduced following treatment with deglycosylation enzymes in absence of any enzyme inhibitors. The 19 kDa product was confirmed not be a glycoprotein when failed to react with ConA stain. The 16/19 kDa forms of the protein were evaluated against T-lymphocytes from Crohn's disease patients and normal controls. T- proliferation assay included controls such as PHA and PPD from M. paratuberculosis. There was not a significant difference between the two forms of the protein (16/19 kDa) against T-cell response from both populations. Overall, the study identified the ORF of the 19 kDa non-glycoprotein from M. paratuberculosis. Moreover, this is the first study which reports that the zoonotic M. paratuberculosis supports posttranslational modification similar to M. tuberculosis and M. leprae pathogens. Although the posttranslational modification component in this 19 kDa nonglycoprotein did not affect T- cell response, the finding is significant toward glycoproteins from M. paratuberculosis and their role in the pathogenesis of this bacterial infection in animals and humans.


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Graduation Date





Naser, Saleh


Master of Science (M.S.)


Burnett College of Biomedical Sciences


Molecular Biology and Microbiology

Degree Program

Molecular Biology and Microbiology








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Masters Thesis (Open Access)