2quu
Dihydroxyacetone phosphate Schiff base intermediate in mutant fructose-1,6-bisphosphate aldolase from rabbit muscle
Structural highlights
FunctionALDOA_RABIT Plays a key role in glycolysis and gluconeogenesis. In addition, may also function as scaffolding protein.[1] Evolutionary Conservation Check, as determined by ConSurfDB. You may read the explanation of the method and the full data available from ConSurf. Publication Abstract from PubMedClass I fructose-1,6-bisphosphate aldolases catalyze the interconversion between the enamine and iminium covalent enzymatic intermediates by stereospecific exchange of the pro(S) proton of the dihydroxyacetone-phosphate C3 carbon, an obligatory reaction step during substrate cleavage. To investigate the mechanism of stereospecific proton exchange, high resolution crystal structures of native and a mutant Lys(146) --> Met aldolase were solved in complex with dihydroxyacetone phosphate. The structural analysis revealed trapping of the enamine intermediate at Lys(229) in native aldolase. Mutation of conserved active site residue Lys(146) to Met drastically decreased activity and enabled trapping of the putative iminium intermediate in the crystal structure showing active site attachment by C-terminal residues 360-363. Attachment positions the conserved C-terminal Tyr(363) hydroxyl within 2.9A of the C3 carbon in the iminium in an orientation consistent with incipient re face proton transfer. We propose a catalytic mechanism by which the mobile C-terminal Tyr(363) is activated by the iminium phosphate via a structurally conserved water molecule to yield a transient phenate, whose developing negative charge is stabilized by a Lys(146) positive charge, and which abstracts the C3 pro(S) proton forming the enamine. An identical C-terminal binding mode observed in the presence of phosphate in the native structure corroborates Tyr(363) interaction with Lys(146) and is consistent with transient C terminus binding in the enamine. The absence of charge stabilization and of a mobile C-terminal catalyst explains the extraordinary stability of enamine intermediates in transaldolases. Stereospecific proton transfer by a mobile catalyst in mammalian fructose-1,6-bisphosphate aldolase.,St-Jean M, Sygusch J J Biol Chem. 2007 Oct 19;282(42):31028-37. Epub 2007 Aug 29. PMID:17728250[2] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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