4u2z
X-ray crystal structure of an Sco GlgEI-V279S/1,2,2-trifluromaltose complex
Structural highlights
FunctionGLGE1_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 PubMedStreptomyces coelicolor (Sco) GlgEI is a glycoside hydrolase involved in alpha-glucan biosynthesis and can be used as a model enzyme for structure-based inhibitor design targeting Mycobacterium tuberculosis (Mtb) GlgE. The latter is a genetically validated drug target for the development of anti-Tuberculosis (TB) treatments. Inhibition of Mtb GlgE results in a lethal buildup of the GlgE substrate maltose-1-phosphate (M1P). However, Mtb GlgE is difficult to crystallize and affords lower resolution X-ray structures. Sco GlgEI-V279S on the other hand crystallizes readily, produces high resolution X-ray data, and has active site topology identical to Mtb GlgE. We report the X-ray structure of Sco GlgEI-V279S in complex with 2-deoxy-2,2-difluoro-alpha-maltosyl fluoride (alpha-MTF, ) at 2.3 A resolution. alpha-MTF was designed as a non-hydrolysable mimic of M1P to probe the active site of GlgE1 prior to covalent bond formation without disruption of catalytic residues. The alpha-MTF complex revealed hydrogen bonding between Glu423 and the C1F which provides evidence that Glu423 functions as proton donor during catalysis. Further, hydrogen bonding between Arg392 and the axial C2 difluoromethylene moiety of alpha-MTF was observed suggesting that the C2 position tolerates substitution with hydrogen bond acceptors. The key step in the synthesis of alpha-MDF was transformation of peracetylated 2-fluoro-maltal into peracetylated 2,2-difluoro-alpha-maltosyl fluoride in a single step via the use of Selectfluor(R). Synthesis of 2-deoxy-2,2-difluoro-alpha-maltosyl fluoride and its X-ray structure in complex with Streptomyces coelicolor GlgEI-V279S.,Thanna S, Lindenberger JJ, Gaitonde VV, Ronning DR, Sucheck SJ Org Biomol Chem. 2015 Jul 2;13(27):7542-50. doi: 10.1039/c5ob00867k. PMID:26072729[2] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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