Designed additives for controlled growth of crystals of phospholipid interacting proteins: Short chain phospholipids

Abstract

A new approach to crystallization of proteins that interact with lipids has been applied to the protein crambin. Short chain phospholipids are water-soluble additives and effectively lower the amount of protein needed to form crambin crystals by lowering protein solubility and inhibiting crystal growth in the fastest growing direction. Compared with optimal crystallization conditions without phospholipid, which gave large crambin crystals (1.5 × 0.7 × 0.5 mm), a 30–60-fold decrease in protein concentration as well as 5-fold decrease in volume were achieved. As a result, the efficiency of crystal production was increased by 150–300-fold. The crystals obtained diffracted beyond 1.5 Å resolution. The most effective additive, phosphotidylcholine, had a size comparable to the proposed binding site on crambin and on the homologous membrane-active toxins. The procedure developed may be useful for crystallization of other phospholipid interacting proteins as well as transmembrane proteins.