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Towards the molecular understanding of glycogen elongation by amylosucrase
Author(s) -
Albenne Cécile,
Skov Lars K.,
Tran Vinh,
Gajhede Michael,
Monsan Pierre,
RemaudSiméon Magali,
AndréLeroux Gwénaëlle
Publication year - 2007
Publication title -
proteins: structure, function, and bioinformatics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.699
H-Index - 191
eISSN - 1097-0134
pISSN - 0887-3585
DOI - 10.1002/prot.21083
Subject(s) - glycogen branching enzyme , chemistry , glycogen debranching enzyme , glycogen , docking (animal) , glycoside hydrolase , biochemistry , glycogen synthase , stereochemistry , enzyme , medicine , nursing
Amylosucrase from Neisseria polysaccharea (AS) is a transglucosidase from the glycoside‐hydrolase family 13 that catalyzes the synthesis of an amylose‐like polymer from sucrose, without any primer. Its affinity towards glycogen is particularly noteworthy since glycogen is the best D ‐glucosyl unit acceptor and the most efficient activator (98‐fold k cat increase) known for this enzyme. Glycogen–enzyme interactions were modeled starting from the crystallographic AS: maltoheptaose complex, where two key oligosaccharide binding sites, OB1 and OB2, were identified. Two maltoheptaose molecules were connected by an α‐1,6 branch by molecular modeling to mimic a glycogen branching. Among the various docking positions obtained, four models were chosen based on geometry and energy criteria. Robotics calculations enabled us to describe a back and forth motion of a hairpin loop of the AS specific B′‐domain, a movement that assists the elongation of glycogen branches. Modeling data combined with site‐directed mutagenesis experiments revealed that the OB2 surface site provides an anchoring platform at the enzyme surface to capture the polymer and direct the branches towards the OB1 acceptor site for elongation. On the basis of the data obtained, a semiprocessive glycogen elongation mechanism can be proposed. Proteins 2007. © 2006 Wiley‐Liss, Inc.