Engineering Orthogonal Polypeptide GalNAc-Transferase and UDP-Sugar Pairs

15 May 2019, Version 1
This content is a preprint and has not undergone peer review at the time of posting.

Abstract

O-GalNAc glycans constitute a major part of the human glycome. They are difficult to study becauseof the complex interplay of 20 distinct glycosyltransferase isoenzymes that initiate this form ofglycosylation, the polypeptide GalNAc transferases (GalNAc-Ts). Despite proven disease relevance,correlating the activity of individual GalNAc-Ts with biological function remains challenging due to alack of tools to probe their substrate specificity in a complex biological environment. Here, wedevelop a “bump–hole” chemical reporter system for studying GalNAc-T activity in vitro. IndividualGalNAc-Ts were rationally engineered to contain an enlarged active site (hole) and probed with anewly-synthesized collection of 20 (bumped) UDP-GalNAc analogs to identify enzyme–substratepairs that retain peptide specificities but are otherwise completely orthogonal to native enzyme–substrate pairs. The approach was applicable to multiple GalNAc-T isoenzymes, including GalNAc-T1 and -T2 that prefer non-glycosylated peptide substrates and GalNAcT-10 that prefers a pre-glycosylated peptide substrate. A detailed investigation of enzyme kinetics and specificities revealed the robustness of the approach to faithfully report on GalNAc-T activity and paves the way forstudying substrate specificities in living systems.

Keywords

glycobiology
glycosyltransferase
bump-hole engineering
mucin
GalNAcT

Supplementary materials

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GalNAcT paper SI
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