Journal Article

Structural and enzymatic analyses of a glucosyltransferase Alr3699/HepE involved in Anabaena heterocyst envelop polysaccharide biosynthesis

Xue-Ping Wang, Yong-Liang Jiang, Ya-Nan Dai, Wang Cheng, Yuxing Chen and Cong-Zhao Zhou

in Glycobiology

Volume 26, issue 5, pages 520-531
Published in print May 2016 | ISSN: 0959-6658
Published online December 2015 | e-ISSN: 1460-2423 | DOI: https://dx.doi.org/10.1093/glycob/cwv167
Structural and enzymatic analyses of a glucosyltransferase Alr3699/HepE involved in Anabaena heterocyst envelop polysaccharide biosynthesis

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Formation of the heterocyst envelope polysaccharide (HEP) is a key process for cyanobacterial heterocyst differentiation. The maturation of HEP in Anabaena sp. strain PCC 7120 is controlled by a gene cluster termed HEP island in addition to an operon alr3698-alr3699, which encodes two putative proteins termed Alr3698/HepD and Alr3699/HepE. Here we report the crystal structures of HepE in the apo-form and three complex forms that bind to UDP-glucose (UDPG), UDP&glucose, and UDP, respectively. The overall structure of HepE displays a typical GT-B fold of glycosyltransferases, comprising two separate β/α/β Rossmann-fold domains that form an inter-domain substrate-binding crevice. Structural analyses combined with enzymatic assays indicate that HepE is a glucosyltransferase using UDPG as a sugar donor. Further site-directed mutageneses enable us to assign the key residues that stabilize the sugar donor and putative acceptor. Based on the comparative structural analyses, we propose a putative catalytic cycle of HepE, which undergoes “open-closed-open” conformational changes upon binding to the substrates and release of products. These findings provide structural and catalytic insights into the first enzyme involved in the HEP biosynthesis pathway.

Keywords: cyanobacteria; crystal structure; glycosyltransferase; GT-B fold; heterocyst envelope polysaccharide

Journal Article.  7663 words.  Illustrated.

Subjects: Carbohydrates

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