Structure and mechanism of action of a novel phosphoglycerate mutase from Bacillus stearothermophilus

Bacillus stearothermophilus phosphoglycerate mutase (PGM), which interconve rts 2- and 3-phosphoglyceric acid (PGA), does not require 2,3-diphosphoglyc eric acid for activity. However, this enzyme does have an absolute and spec ific requirement for Mn2+ ions for catalysis, Here we report the crystal st ructure of this enzyme complexed with 3PGA and manganese ions to 1.9 Angstr om resolution; this is the first crystal structure of a diphosphoglycerate- independent PGM to be determined. This information, plus the location of th e two bound Mn2+ ions and the 3PGA have allowed formulation of a possible c atalytic mechanism for this PGM. In this mechanism Mn2+ ions facilitate the transfer of the substrate's phosphate group to Ser62 to form a phosphoseri ne intermediate. In the subsequent phosphotransferase part of the reaction, the phosphate group is transferred from Ser62 to the O2 or O3 positions of the reoriented glycerate to yield the PGA product. Site-directed mutagenes is studies were used to confirm our mechanism and the involvement of specif ic enzyme residues in Mn2+ binding and catalysis.