Structural basis for arginine glycosylation of host substrates by bacterial effector proteins

15 pags, 5 figs
The bacterial effector proteins SseK and NleB glycosylate host proteins on arginine residues, leading to reduced NF-κB-dependent responses to infection. Salmonella SseK1 and SseK2 are E. coli NleB1 orthologs that behave as NleB1-like GTs, although they differ in protein substrate specificity. Here we report that these enzymes are retaining glycosyltransferases composed of a helix-loop-helix (HLH) domain, a lid domain, and a catalytic domain. A conserved HEN motif (His-Glu-Asn) in the active site is important for enzyme catalysis and bacterial virulence. We observe differences between SseK1 and SseK2 in interactions with substrates and identify substrate residues that are critical for enzyme recognition. Long Molecular Dynamics simulations suggest that the HLH domain determines substrate specificity and the lid-domain regulates the opening of the active site. Overall, our data suggest a front-face Si mechanism, explain differences in activities among these effectors, and have implications for future drug development against enteric pathogens.
This work was supported by Grants from the National Research Foundation of Korea (NRF) funded by the Korean government (MEST) (NRF- 2016R1A2B2013305, 2016R1A5A1010764, 2014R1A4A1008625, 2017M3A9F6029755 and 2017R1A2B3006704), the Strategic Initiative for Microbiomes in Agriculture and Food funded by Ministry of Agriculture, Food and Rural Affairs (918012-4) and Brain Korea 21 PLUS Project for Medical Science. This work was also supported by Grants AI093913 and AI127973 from the National Institutes of Health (to P.R.H.). We also thank ARAID and MEC (CTQ2013-44367-C2-2-P, BFU2016-75633-P to R.H-G.), and the DGA (group number E34_R17) for financial support. S.M. acknowledges a postgraduate studentship from the School of Pharmacy of the University of East Anglia. J.A. and S W. acknowledge funding from BBSRC through a research grant (BB/P010660/1) and a DTP PhD studentship, respectively.