Mechanism of Ionic Strength Dependence of Crystal Growth Rates in a Subtilsin Variant
David T. Gallagher, Q Pan, G L. Gilliland
An orthorhombic crystal form of subtilisin exhibits a systematic variation in growth rates of its three unique faces, resulting in pronounced morphology variations, depending on ionic strength. Several common salts cause a concentration-dependent change in the crystal habit from thin plates to isometric bars. The effect is analyzed in terms of the four crystal contacts in the 1.75 A resolution X-ray structure. Morphological growth fronts and the rate-limiting attachment step for growth of each face are considered, and it is concluded that ion screening of a carboxyl-carboxyl interaction in one crystal contact plays a key role in the salt-morphology effect.
Journal of Crystal Growth
crystal structure, ion screening, lattice packing, protein crystal growth, subtilisin