Refined crystal structure of mitochondrial malate dehydrogenase from porcine heart and the consensus structure for dicarboxylic acid oxidoreductases.

The crystal structure of mitochondrial malate dehydrogenase from porcine heart contains four identical subunits in the asymmetric unit of a monoclinic cell. Although the molecule functions as a dimer in solution, it exists as a tetramer with 222 point symmetry in the crystal. The crystallographic refinement was facilitated in the early stages by using weak symmetry restraints and molecular dynamics. The R-factor including X-ray data to 1.83-A resolution was 21.1%. The final root mean square deviation from canonical values is 0.015 A for bond lengths and 3.2 o for bond angles. The resulting model of the tetramer includes independent coordinates for each of the four subunits allowing an internal check on the accuracy of the model