Metallfluoride als Analoga für Studien an Phosphoryltransferenzymen

Abstract

In 1994, the protein structure of a transition state analogue for G1, a small G protein, heralded a new field of research into the structure and mechanism of enzymes that manipulate transfer of the phosphoryl (PO3-) group. It was based on a protein complex of GDP and AlF4that mimicked the transition state for hydrolysis of GTP. The growing list of enzyme structures that embrace metal fluorides, MFx, as ligands that imitate either the phosphoryl group or a phosphate, now exceeds 80 per triennium. They fall into three distinct geometrical classes: (i) Tetrahedral complexes based on BeF3-, mimic ground state phosphates, (ii) Octahedral complexes, primarily AlF4-, mimic "inline" anionic transition state for phosphoryl transfer, and (iii) Trigonal bipyramidal complexes additionally mimic the tbp stereochemistry of the transition state and are represented by MgF3and putative AlF3 0 complexes. Their interpretation has provided a deeper mechanistic understanding of the behavior and role of phosphate monoesters in molecular biology. This review challenges the existence of AlF3 0 and MgF4 = as real species in protein complexes and questions the relevance for enzymes of physical organic chemistry and model studies that are waterbased for phosphoryl group transfer. It proposes a new interpretation of the role of general acid-base catalysis. Yi Jin took her BSc chemistry in Xiamen University, China followed by an MSc in organic chemistry in the group of Prof. Yufen Zhao. She received her PhD in 2012 followed by a one-year postdoc under the guidance of Profs. J.P. Waltho and G. M. Blackburn in the University of Sheffield, UK. In 2014, she moved to the group of Prof. G. J. Davies in YSBL, University of York, UK. Her research interests involve mechanistic studies of disease-relevant phosphoryl transfer enzymes and carbohydrate processing enzymes using chemical, NMR, molecular biology, and crystallographic approaches. Michael Blackburn is Emeritus Professor of Biomolecular Chemistry in Sheffield University and a founding member of the Krebs Institute. His undergraduate and post-doctoral career in Cambridge University led him in 1961 into the biological chemistry of phosphorus under Alexander Todd. He has worked on nucleotides, their analogs, and the enzymes that use them at the interface of chemistry and molecular biology for over 50 years. Most recently, he has focused on the unique paradox between their structural stability and kinetic lability.

A GAP‐GTPase‐GDP‐Pi Intermediate Crystal Structure Analyzed by DFT Shows GTP Hydrolysis Involves Serial Proton Transfers

“…Very significantly, this first isomeric structure has an O B ‐P G ‐O G angle of 176°, thus maintaining the “in‐line” character of the TS to the first intermediate complex, also manifest in the X‐ray structure (Figure c). This angle changes to 150° only on subsequent formation of the LBHB between O3G and O3B (Figure c), conflicting with the need for “bending the formed P−O bond for optimal phosphoryl transfer”, advocated elsewhere …”

“…Our result on LBHB for these two isomers in the 3rd and 4th structures now provides a clear explanation for this behavior: O3B cannot be a nucleophile towards PG: by accepting three H‐bonds from O3G, Arg85′, and Ala15 it has no electron pair available for in‐line nucleophilic interaction with PG. This is a powerful example of phosphoryl transfer being suppressed by H‐bonding between nucleophile and phosphoryl oxygen that denies bonding orbital overlap …”