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 PubMed
GlgE is a maltosyltranferase involved in alpha-glucan biosynthesis in bacteria that has been genetically validated as a target for tuberculosis therapies. Crystals of the Mycobacterium tuberculosis enzyme diffract at low resolution so most structural studies have been with the very similar Streptomyces coelicolor GlgE isoform 1. Although the donor binding site for alpha-1-phosphate had been previously structurally defined, the acceptor site had not. Using mutagenesis, kinetics and protein crystallography of the S. coelicolor enzyme, we have now identified the +1 to +6 sub-sites of the acceptor/product, which overlap with the known cyclodextrin binding site. The sugar residues in the acceptor sub-sites +1 to +5 are oriented such that they disfavour the binding of malto-oligosaccharides that bear branches at their 6 positions, consistent with the known acceptor chain specificity of GlgE. A secondary binding site remote from the catalytic centre was identified that is distinct from one reported for the M. tuberculosis enzyme. This new site is capable of binding a branched alpha-glucan, and is most likely involved in guiding acceptors towards the donor site because its disruption kinetically compromises the ability of GlgE to extend polymeric substrates. However, disruption of this site, which is conserved in the S. venezuelae GlgE enzyme, did not affect the growth of S. venezuelae or the structure of the polymeric product. The acceptor sub-sites +1 to +4 in the S. coelicolor enzyme are well conserved in the M. tuberculosis enzyme so their identification could help inform the design of inhibitors with therapeutic potential.
Ligand-bound structures and site-directed mutagenesis identify the acceptor and secondary binding sites of Streptomyces coelicolor maltosyltransferase GlgE.,Syson K, Stevenson CE, Miah F, Barclay JE, Tang M, Gorelik A, Rashid AM, Lawson DM, Bornemann S J Biol Chem. 2016 Aug 16. pii: jbc.M116.748160. PMID:27531751[2]
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.
References
- ↑ Syson K, Stevenson CE, Rejzek M, Fairhurst SA, Nair A, Bruton CJ, Field RA, Chater KF, Lawson DM, Bornemann S. Structure of a Streptomyces maltosyltransferase GlgE: a homologue of a genetically validated anti-tuberculosis target. J Biol Chem. 2011 Sep 13. PMID:21914799 doi:10.1074/jbc.M111.279315
- ↑ Syson K, Stevenson CE, Miah F, Barclay JE, Tang M, Gorelik A, Rashid AM, Lawson DM, Bornemann S. Ligand-bound structures and site-directed mutagenesis identify the acceptor and secondary binding sites of Streptomyces coelicolor maltosyltransferase GlgE. J Biol Chem. 2016 Aug 16. pii: jbc.M116.748160. PMID:27531751 doi:http://dx.doi.org/10.1074/jbc.M116.748160
