The crystal packing interactions of two different crystal forms of bovine Ribonuclease A

Abstract The crystal packing interactions of two crystal forms of bovine Ribonuclease A are compared. One form, grown in 43% t -butanol at pH 5.3, has space group P2 1 , one molecule in the asymmetric unit, a = 30.18 A, b = 38.32 A, c = 53.32 A and β = 105.85°. The other crystal form is grown in 3M CsCl and acetate buffer at pH 5.1, has space group P2 1 2 1 2 1 , two molecules in the asymmetric unit, a = 53.14 A, tb = A and c = 73.64 A. An analysis of the crystal packing interactions, including solvent bridging, the indicates that The high-alcohol crystal form of Ribonuclease A has a balance of hydrogen bonding, electrostatic and Van der Waals interactions. In contrast, the high-salt crystal packing forces are dominated by Van der Waals interactions, but at the dimer interface of the molecules in this crystal form the interactions have a large electrostatic component. The electrostatic interactions of the dimer may be due to a rearrangement in the charge-charge interactions at the active site, a direct result of the presence of the inhibitor, deoxythymidine, covalently bound to His 12.