Active Form ofPseudomonas mevalonii3-Hydroxy-3-methylglutaryl Coenzyme A Reductase

Based on multiple gel permeation chromatographic experiments, we report a Stokes radius of 59.7 Å forPseudomonas mevalonii3-hydroxy-3methylglutaryl coenzyme A reductase (HMG-CoA reductase; EC 1.1.1.88) and its His381Asn, His381Gln, and His381Lys mutant enzymes. Comparison of this Stokes radius with the radius calculated from the crystal structure indicated that the active form ofP. mevaloniiHMG-CoA reductase was a hexamer and not a dimer as previously thought. The Stokes radius, anS_20,wof 11.0, and an estimated$\text{V}\text{̄}$of 0.723 were used in the Svedberg equation to calculate an anhydrous molecular mass of 270,084 Da forP. mevaloniiHMG-CoA reductase (monomer mass 45,538 Da), consistent with the enzyme being a hexamer in solution. The Stokes radii of all standard proteins examined correlated with the inverse error function complement of their partition coefficient,K_d.K_ddid not correlate with logarithm of the standard protein's molecular weight. Eight nonstandard proteins had Stokes radii that matched their crystallographic radii of longest axis. This indicated that the frozen conformation of a protein in its crystal form can dictate restraints on its shape in solution.