Mechanism of catalysis of the cofactor-independent phosphoglycerate mutasefrom Bacillus stearothermophilus - Crystal structure of the complex with 2-phosphoglycerate

The structure of the complex between the 2,3-diphosphoglycerate-independent phosphoglycerate mutase (iPGM) hom Bacillus stearothennophilus and its 3-p hosphoglycerate substrate has recently been solved, and analysis of this st ructure allowed formulation of a mechanism for iPGM catalysis. In order to obtain further evidence for this mechanism, we have solved the structure of this iPGM complexed with 2-phoshoglycerate and two Mn2+ ions at 1.7-Angstr om resolution. The structure consists of two different domains connected by two loops and interacting through a network of hydrogen bonds. This struct ure is consistent with the proposed mechanism for iPGM catalysis, with the two main steps in catalysis being a phosphatase reaction removing the phosp hate from 2- or 3-phosphoglycerate, generating an enzyme-bound phosphoserin e intermediate, followed by a phosphotransferase reaction as the phosphate is transferred from the enzyme back to the glycerate moiety, The structure also allowed the assignment of the function of the two domains of the enzym e, one of which participates in the phosphatase reaction and formation of t he phosphoserine enzyme intermediate, with the other involved in the phosph otransferase reaction regenerating phosphoglycerate. Significant structural similarity has also been found between the active site of the iPGM domain catalyzing the phosphatase reaction and Escherichia coli alkaline phosphata se.