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

Bacillus stearothermophilus phosphoglycerate mutase (PGM), which interconverts 2‐ and 3‐phosphoglyceric acid (PGA), does not require 2,3‐diphosphoglyceric acid for activity. However, this enzyme does have an absolute and specific requirement for Mn2+ ions for catalysis. Here we report the crystal structure of this enzyme complexed with 3PGA and manganese ions to 1.9 Å resolution; this is the first crystal structure of a diphosphoglycerate‐independent PGM to be determined. This information, plus the location of the two bound Mn2+ ions and the 3PGA have allowed formulation of a possible catalytic mechanism for this PGM. In this mechanism Mn2+ ions facilitate the transfer of the substrate's phosphate group to Ser62 to form a phosphoserine 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 mutagenesis studies were used to confirm our mechanism and the involvement of specific enzyme residues in Mn2+ binding and catalysis.