Confirmation of a Trimeric Subunit Arrangement for 2-Keto-3-deoxy-6-phosphogluconic Aldolase Using X-ray Crystallographic Methods

Abstract 2-Keto-3-deoxy-6-phosphogluconate aldolase of Pseudomonas putida crystallizes from ammonium sulfate at pH 3.5 in the cubic system with unit cell dimensions of 103.1 ± 0.2 A in the space group P213 which has 12 equivalent positions. From variable equilibrium density measurements and the salt-free density determination, the molecular weight per unit cell was calculated to be 326,000 or 27,200 ± 2,000 per asymmetric unit, in good agreement with other chemical and physical data. Consideration of the mass per asymmetric unit, the symmetry elements of P213, and the results of chemical and physical solution studies suggest that the molecules are assemblages of trimers in the crystal with the subunits related by a 3-fold rotation axis.