4XSO image
Entry Detail
PDB ID:
4XSO
Keywords:
Title:
Crystal structure of apo-form Alr3699/HepE from Anabaena sp. strain PCC 7120
Biological Source:
PDB Version:
Deposition Date:
2015-01-22
Release Date:
2016-01-13
Method Details:
Experimental Method:
Resolution:
2.01 Å
R-Value Free:
0.24
R-Value Work:
0.19
R-Value Observed:
0.19
Space Group:
C 2 2 21
Macromolecular Entities
Polymer Type:polypeptide(L)
Description:Alr3699 protein
Chain IDs:A (auth: B), B (auth: A)
Chain Length:388
Number of Molecules:2
Biological Source:Nostoc sp. (strain PCC 7120 / UTEX 2576)
Ligand Molecules
Primary Citation
Structural and enzymatic analyses of a glucosyltransferase Alr3699/HepE involved in Anabaena heterocyst envelop polysaccharide biosynthesis
Glycobiology 26 520 531 (2016)
PMID: 26692049 DOI: 10.1093/glycob/cwv167

Abstact

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.

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