Anionic charge is prioritized over geometry in aluminum and magnesium fluoride transition state analogs of phosphoryl transfer enzymes.
Phosphoryl transfer reactions are ubiquitous in biology and metal fluoride complexes have played a central role in structural approaches to understanding how they are catalyzed. In particular, numerous structures of AlFx-containing complexes have been reported to be transition state analogs (TSAs). A survey of nucleotide kinases has proposed a correlation between the pH of the crystallization solution and the number of coordinated fluorides in the resulting aluminum fluoride TSA complexes formed. Enzyme ligands crystallized above pH 7.0 were attributed to AlF3, whereas those crystallized at or below pH 7.0 were assigned as AlF4-. We use 19F NMR to show that for beta-phosphoglucomutase from Lactococcus lactis, the pH-switch in fluoride coordination does not derive from an AlF4- moiety converting into AlF3. Instead, AlF4- is progressively replaced by MgF3- as the pH increases. Hence, the enzyme prioritizes anionic charge at the expense of preferred native trigonal geometry over a very broad range of pH. We demonstrate similar behavior for two phosphate transfer enzymes that represent typical biological phosphate transfer catalysts: an amino acid phosphatase, phosphoserine phosphatase from Methanococcus jannaschii and a nucleotide kinase, phosphoglycerate kinase from Geobacillus stearothermophilus. Finally, we establish that at near-physiological ratios of aluminum to magnesium, aluminum can dominate over magnesium in the enzyme-metal fluoride inhibitory TSA complexes, and hence is the more likely origin of some of the physiological effects of fluoride.
Baxter
Nicola J
NJ
Department of Molecular Biology and Biotechnology, University of Sheffield, Sheffield S10 2TN, United Kingdom.
Blackburn
G Michael
GM
Marston
James P
JP
Hounslow
Andrea M
AM
Cliff
Matthew J
MJ
Bermel
Wolfgang
W
Williams
Nicholas H
NH
Hollfelder
Florian
F
Wemmer
David E
DE
Waltho
Jonathan P
JP
D017607:Aluminum Compounds / Q000737:chemistry*; D000838:Anions / Q000737:chemistry; D001665:Binding Sites; D002384:Catalysis; D005459:Fluorides / Q000737:chemistry*; D001411:Geobacillus stearothermophilus / Q000201:enzymology; D006863:Hydrogen-Ion Concentration; D008024:Ligands; D017616:Magnesium Compounds / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy / Q000379:methods / Q000592:standards; D008958:Models, Molecular; D008968:Molecular Conformation; D010735:Phosphoglycerate Kinase / Q000737:chemistry*; D010744:Phosphoric Monoester Hydrolases / Q000737:chemistry*; D017875:Phosphotransferases (Phosphomutases) / Q000737:chemistry*; D017434:Protein Structure, Tertiary; D012015:Reference Standards
D017607:Aluminum Compounds; D000838:Anions; D008024:Ligands; D017616:Magnesium Compounds; C031288:magnesium fluoride; D010735:Phosphoglycerate Kinase; D010744:Phosphoric Monoester Hydrolases; C022394:phosphoserine phosphatase; D017875:Phosphotransferases (Phosphomutases); C512509:beta-phosphoglucomutase, Lactococcus lactis; D005459:Fluorides; C032311:aluminum fluoride