Prediction of o-glycosylation pathways in Mycobacterial immunogenic proteins
Authors: Yari Shamsi , Tasbiti Alireza Hadizadeh , Khanipour Sharareh , Abdolrahimi Farid , Masoumi Morteza , Nematollahi Ali Noor , Davari Mehdi , Sakhaee Fatemeh , Siadat Seyed Davar 
Published: January 2021

Aims and objectives:
There is an emergence need to identifying Mycobacterial proteins of value to diagnostic assays and vaccine formulations. Glycosylation is an important post-translational modification of proteins and affects more than half of all the proteins in a cell. O-linked glycosylation refers to the event in which a carbohydrate is covalently linked to the hydroxyl group of serine or threonine. This modification influences a number of properties of proteins including proteolytic resistance, solubility, immunological properties and ligand binding. Host cells can bind to Mycobacterial cell wall carbohydrates via a class of surface localized or secreted proteins known as lectins, and these interactions strongly contribute to bacterial adhesion and uptake, and are also associated with the capability of Mtb to survive. This study represents the attempt to predict o-glycosylation pathways of immunogenic TB proteins as potential therapeutic strategies against TB.

Methods:
A Mycobacterium tuberculosis culture filtrate enriched with mannose-containing proteins that were purified by conA-Affinity chromatography. One and two dimensional gel electrophoresis carried out by standard methods. Gel staining procedures are based on the periodic Acid-Schiff reaction. The Protein spots of interest were excised from the gel and then analysis by MALDI Mass Spectrometry. GlycoPP software, Version 1.0, was used for glycosylation prediction and protein sequences.

Results:
Protein bands or spots were excised from the gel and analyzed by mass spectrometry. These proteins have O-glycosite residue and a glycan attached covalently and enzymatically at amide or hydroxyl group which includes Rv0475, Rv3367, Rv3699, Rv0251c, Rv2558 and Rv1284. Rv0475 has 17 Potential O-Linked Glycosylated Sites but 6 sites of Potential Glycosylated. Rv3367 has 67 Potential O-Linked Glycosylated Sites and 55 sites of Potential Glycosylated. Additionally, Rv3699 has 26 Potential O-Linked Glycosylated Sites and 10 sites Potential Glycosylated.

Conclusions:
This study may be shown the role of glycoprotein's in Mycobacterium pathogenesis, disease development, and its implications in drug development. All of these proteins have several putative antigenic epitopes and induces an immune response especially production of antibodies. In addition, Rv3367as a member of the Mycobacterium tuberculosis PE family and PGRS subfamily, gly-rich proteins have carbohydrate moieties and also are known to play a role in several pathological processes. Because of the importance of M.tuberculosis immunogenic antigens, the availability of the secretion and glycosylation of MTB proteins is a tool that will allow a deeper understanding of role these proteins play in the pathogenesis of disease and provide the basis for more sensitive and discriminative clinical diagnostic tests and improving to formulate new Mycobacterial vaccines.