3zss
From Proteopedia
Apo form of GlgE isoform 1 from Streptomyces coelicolor
Structural highlights
Function[GLGE1_STRCO] Maltosyltransferase that uses maltose 1-phosphate (M1P) as the sugar donor to elongate linear or branched alpha-(1->4)-glucans. Maltooligosaccharides with a degree of polymerization (DP) superior or equal to 4 are efficient acceptors, with DP6 being optimal in the GlgE-catalyzed polymerization with M1P. Is specific for the alpha-anomer of M1P as substrate, since the beta-anomer of M1P gives no activity. Alpha-D-glucose 1-phosphate cannot serve as a donor substrate, but alpha-maltosyl fluoride is an efficient donor in vitro. Exhibits an alpha-retaining catalytic mechanism, with evidence that maltooligosaccharide acceptors are extended at their non-reducing ends. Is also able to catalyze the reverse reaction in vitro, releasing M1P from glycogen or maltoheptaose in the presence of inorganic phosphate. Also catalyzes disproportionation reactions through maltosyl transfer between maltooligosaccharides. Is probably involved in a branched alpha-glucan biosynthetic pathway from trehalose, together with TreS, Mak and GlgB.[1] Publication Abstract from PubMedGlgE is a recently identified (1-->4)-alpha-D-glucan:phosphate alpha-D-maltosyltransferase involved in alpha-glucan biosynthesis in bacteria and is a genetically validated anti-tuberculosis drug target. It is a member of the GH13_3 CAZy sub-family for which no structures were previously known. We have solved the structure of GlgE isoform I from Streptomyces coelicolor and shown that this enzyme has the same catalytic and very similar kinetic properties to GlgE from Mycobacterium tuberculosis. The S. coelicolor enzyme forms a homodimer with each subunit comprising five domains including a core catalytic alpha-amylase-type domain A with a (beta/alpha)8 fold. This domain is elaborated with domain B and two inserts that are specifically configured to define a well conserved donor pocket capable of binding maltose. Domain A, together with domain N from the neighbouring subunit, forms a hydrophobic patch that is close to the maltose binding site and capable of binding cyclodextrins. Cyclodextrins competitively inhibit the binding of maltooligosaccharides to the S. coelicolor enzyme, showing that the hydrophobic patch overlaps with the acceptor binding site. This patch is incompletely conserved in the M. tuberculosis enzyme such that cyclodextrins do not inhibit this enzyme, despite acceptor length specificity being conserved. The crystal structure reveals two further domains, C and S, the latter being a helix bundle not previously reported in GH13 members. The structure provides a framework for understanding how GlgE functions and will help guide the development of inhibitors with therapeutic potential. Structure of a Streptomyces maltosyltransferase GlgE: a homologue of a genetically validated anti-tuberculosis target.,Syson K, Stevenson CE, Rejzek M, Fairhurst SA, Nair A, Bruton CJ, Field RA, Chater KF, Lawson DM, Bornemann S J Biol Chem. 2011 Sep 13. PMID:21914799[2] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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