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Enzyme Catalysed Phosphoryl Transfer Reactions: Magnesium and Other Metal Fluorides as Substrate and Transition-State Analogs
|George M. Blackburn
Sheffield University, Chemistry Department, Brook Hill, Sheffield S37HF, United Kingdom
Magnesium trifluoride, MgF3-, has been assigned [1, 2] and under-assigned  as the molecular species seen in x-ray structures of trigonal-bipyramidal species (tbp) of enzymes catalysing phosphoryl transfer. A structure of ß-phosphoglucomutase (ßPGM) complexed with G6P has been presented as a pentacovalent tbp phosphorus intermediate . Our alternative attribution of MgF3- as the tbp species  has been strongly rejected .
Kinetic, spectroscopic, and structural data confirms MgF3- as a TSA for ßPGM. F- is a strong inhibitor for ßPGM and 19F NMR analysis shows three F- ions are recruited into the active site of the enzyme in the presence of G6P. NOE analysis using 15N,2H-labelled ßPGM shows 4 amino acids in close contact with two F-; the third F- is co-ordinated to a catalytic Mg2+ ion. This accurately locates the binding site for MgF3- which is further co-ordinated to G6P C1-OH group and to Asp8. In examples of metal fluoride complexes of phosphoryl transfer enzymes identified by x-ray analysis, the presence of F- (rather than OH-) must be inferential at the resolutions achieved. Our results constitute the first direct observation of a metal fluoride complex as a TSA for a phosphoryl transfer enzyme. The bonding in the tbp accurately portrays the transition state for phosphoryl transfer in ßPGM and reveals the details of protein catalysis.
 D. L. Graham, P. N. Lowe et al., Chem. Biol. 2002, 9, 375-381.
Presentation: oral at 18th Conference on Physical Organic Chemistry, Symposium 1, by George M. Blackburn
See On-line Journal of 18th Conference on Physical Organic Chemistry
Submitted: 2006-05-19 14:06 Revised: 2009-06-07 00:44