Molecular symmetry of glyceraldehyde-3-phosphate dehydrogenase from Bacillus coagulans

The thermolabile glyceraldehyde-3-phosphate dehydrogenase from the facultative thermophile Bacillus coagulans has a crystallographically exact 2-fold rotation axis of symmetry in one of its orthorhombic crystal forms (Lee et al., 1982). Using various crystallographic techniques, we have now identified this axis to be the molecular R-axis, which is the symmetry axis that relates the two subunits that form each active site of the tetrameric enzyme. This is in contrast to the symmetry of the human skeletal muscle enzyme wherein the crystallographically exact axis was found to be the Q-axis (Buehner et al., 1974). This finding could have important implications for the possible mechanism for the allosteric behavior of this molecule.