Investigation of thioester domains and ester domains in selected TIE proteins of Gram-positive pathogens

Abstract

Pathogenic and commensal microbes rely on surface proteins to facilitate adhesion to and invasion of host cells. Colonization and infection require specific molecular interactions at the host-microbe interface that involve microbial surface adhesins. Mechanisms of binding by bacterial adhesins are attractive targets for development of novel antimicrobials. To mediate strong attachment, bacterial adhesion complexes typically present extensive, multivalent binding interfaces. Preliminary results show that wide and diverse ranges of Gram-positive bacteria have evolved a mechanism for covalent bond formation with specific host factors via a pathogen-encoded reactive internal thioester (TED). Covalent binding of bacteria to host tissue providing rapid, mechanically resistant attachment may be particularly advantageous under conditions of shear stress. This research thesis shows an interaction between relevant human tissues and TEDs from Streptococcus pneumoniae, Streptococcus pyogenes and vancomycin-resistant Staphylococcus aureus (VRSA) proteins, as the first representatives of a newly identified class of Gram- positive “TIE” proteins comprised of repetitive domains containing three different self-generating crosslinks between amino acid side chains: thioester, isopeptide and ester bonds. Moreover this research provides evidence, that this interaction may be blocked using small molecule inhibitors. In this work, we also show biophysical and structural studies of ester domains, and single amino acid mutants thereof, from Streptococcus pneumoniae and VRSA using a combination of circular dichroism spectroscopy (CD), NMR spectroscopy and X- ray crystallography) and we present two ED structures.

Over all, this research brings us a step closer to understanding the mechanisms of action of TIE proteins, which are potential new targets to prevent bacterial colonization of human tissues.

Date of Award	21 Jun 2017
Original language	English
Awarding Institution	University of St Andrews
Supervisor	Uli Schwarz-Linek (Supervisor)