The Ag38-rec Mycobacterium tuberculosis Antigen as a New Candidate Marker for The Diagnostic of Tuberculosis Meningitis: In Silico Approach

Tuberculous meningitis (TBM) is the most severe extrapulmonary infection caused by Mycobacterium tuberculosis (Mtb). An accurate diagnosis of TBM has yet to be established. Periplasmic Phosphate Binding Lipoprotein is a seropositive marker for TBM diagnosis. In the previous study, we tested antigen Ag38 recombinant from local strain and showed potential as a serodiagnosis agent candidate. This study aimed to analyze the variability gene of PstS1 and Ag38 rec and to identify the immune-dominant epitope protein PstS1 and 38recp. The PstS1 gene sequence of Mtb from the Mycobrowser database and 38kDa rec was obtained from the previous study. Variability gene of PstS1 and Ag38 rec was identified through the alignment of both genes. To predict the signal peptide in the PstS1 protein sequence, TargetP -2.0 was used. The candidate epitope on the mature protein was predicted with Bepipred 2.0 on the IEDB server. The results of Bepipred 2.0 were then compared with the Emini Surface Accessibility tool, Karplus and Schulz Flexibility tool, and Parker Hydrophilicity tool. The epitope obtained was further analyzed for antigenicity prediction. The position of the epitope on the 3D structure of the PstS1 protein was modeled with the help of the Ellipro predictor. The alignment result of gene PstS1 with Ag38reg contains an anonymous N base, but there were no mutations. Based on Target-P 2, it was found that the PstS1 protein contains a signal peptide with a truncation site at residues 24 and 25. From the results of the epitope prediction, ten candidate epitopes were obtained. Based on the antigenicity analysis, candidate epitopes were finally obtained. Of the five epitopes, two epitopes were similar to PstS1 Mtb protein crystallization results. Two epitopes are AGFASKTPANQAISMID-GPAPD and QGTIKTWDDPQIAALNPGVNLP. Thus, two potential epitope candidates are diagnostic biomarkers, namely AGFASKTPANQAISMIDGPAPD and QGTIKTWDDPQIAALNPGVNLP. However, further research is needed to validate these epitopes using the tool diagnosis TBM.