An Insight into the Function of Family IV GtrABC: Putative Glycosyltransferase Proteins Present in Some Serovars of Non-Typhoidal Salmonella

The O-antigen is a component of the LPS, a surface molecule that covers the surface of bacteria including Salmonella. The O-antigen has an important role in infection as it is recognized by the host immune system. Salmonella is a Gram-negative foodborne bacterial pathogen causing inflammation in the gut and diarrhea or an invasive typhoidal disease. The O-antigen of Salmonella has been known to be modified by gtr genes, a group of three genes: gtrA, gtrB and gtrC found within an operon, which have been found to mediate the addition of a glucose molecule on to the repeating unit of the O-antigen. However, the family IV Gtr proteins’ function has not been identified but a study has shown that they may be needed for persistence within a host. This project studied the expression of these genes, using a beta-galactosidase assay and RT-qPCR, and looked at their ability to mediate modifications to the Salmonella O-antigen using LPS extraction and analysis techniques. The results of this study show expression from transcriptional start sites within the operon suggesting that GtrC(IV) can be expressed independently of the remainder of the operon. The results also show that GtrAB(IV) can replace the function of other GtrAB proteins of known function indicating that they are able to bind and transfer a glucose to a GtrC protein. However, this study was not able to show that GtrC(IV) was targeting the O-antigen, it also found that there is no common sugar amongst the family IV core O-antigens. This suggests that either further unidentified modifications are needed to be made to the O-antigen or the O-antigen is not the target of GtrC(IV).