Protein NMR Studies of substrate binding to human blood group A and B glycosyltransferases.
Related Articles Protein NMR Studies of substrate binding to human blood group A and B glycosyltransferases.
Chembiochem. 2017 Mar 03;:
Authors: Peters T, Grimm LL, Weissbach S, Flügge F, Begemann N, Palcic M
Abstract
Donor and acceptor substrate binding to human blood group A and B glycosyltransferases (GTA, GTB) has been studied by a variety of protein NMR experiments. Prior crystallographic studies have shown these enzymes to adopt an open conformation in the absence of substrates. Binding of either the donor substrate UDP-Gal, or of UDP induces a semi-closed conformation. In the presence of both, donor- and acceptor substrates, the enzymes shift towards a closed conformation with ordering of an internal loop and the C-terminal residues, which then completely cover the donor-binding pocket. Chemical shift titrations of uniformly 2H,15N labeled GTA or GTB with UDP affected about 20% of all cross peaks in 1H,15N-TROSY-HSQC spectra reflecting substantial plasticity of the enzymes. On the other hand, it is this conformational flexibility that impedes NH backbone assignments. Chemical shift perturbation experiments using ?1-13C-methyl Ile labeled samples revealed two Ile residues, Ile123 at the bottom of the UDP binding pocket, and Ile192 as part of the internal loop that were significantly disturbed upon stepwise addition of UDP and H-disaccharide, also revealing long-range perturbations. Finally, methyl TROSY based relaxation dispersion experiments do not reveal ?s to ms time scale motions. Although this study reveals substantial conformational plasticity of GTA and GTB it remains enigmatic how binding of substrates shifts the enzymes into catalytically competent states.
PMID: 28256109 [PubMed - as supplied by publisher]
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