5vje
Class II fructose-1,6-bisphosphate aldolase of Escherichia coli with D-glucitol 1,6-bisphosphate
Structural highlights
FunctionALF_ECOLI Catalyzes the aldol condensation of dihydroxyacetone phosphate (DHAP or glycerone-phosphate) with glyceraldehyde 3-phosphate (G3P) to form fructose 1,6-bisphosphate (FBP) in gluconeogenesis and the reverse reaction in glycolysis.[1] Publication Abstract from PubMedCrystal structures of two bacterial metal (Zn) dependent D-fructose 1,6-bisphosphate (FBP) aldolases in complex with substrate, analogues, and triose-P reaction products were determined to 1.5-2.0 A resolution. The ligand complexes cryotrapped in native or mutant H. pylori aldolase crystals enabled a novel mechanistic description of FBP C3-C4 bond cleavage. The reaction mechanism uses active site remodelling during the catalytic cycle implicating relocation of the Zn cofactor that is mediated by conformational changes of active site loops. Substrate binding initiates conformational changes, triggered upon P1-phosphate binding, which liberates the Zn chelating His180, allowing it to act as a general base for the proton abstraction at the FBP C4-hydroxyl group. A second zinc chelating His83 hydrogen bonds the substrate C4- hydroxyl group and assists cleavage by stabilizing the developing negative charge during proton abstraction. Cleavage is concerted with relocation of the metal cofactor from an interior to a surface exposed site, thereby stabilizing the nascent enediolate form. Conserved residue Glu142 is essential for protonation of the enediolate form, prior to product release. A D-tagatose 1,6-bisphosphate enzymatic complex reveals how His180 mediated proton abstraction controls stereospecificity of the cleavage reaction. Recognition and discrimination of the reaction products, dihydroxyacetone-P and D-glyceraldehyde-3-P, occurs via charged hydrogen bonds between hydroxyl groups of the triose-Ps and conserved residues, Asp82 and Asp255, respectively, and are crucial aspects of the enzyme's role in gluconeogenesis. Conformational changes in mobile loops beta5-alpha7 and beta6-alpha8 (containing catalytic residues Glu142 and His180, respectively) drive active site remodelling enabling the relocation of the metal cofactor. Active site remodeling during the catalytic cycle in metal-dependent fructose-1,6-bisphosphate aldolases.,Jacques B, Coincon M, Sygusch J J Biol Chem. 2018 Mar 28. pii: RA117.001098. doi: 10.1074/jbc.RA117.001098. PMID:29593097[2] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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