High-level expression, purification, and crystallization of recombinant rat leukotriene C4 synthase from the yeast Pichia pastoris

Leukotriene C4 synthase (LTC4S) is a member of the MAPEG family of integral membrane proteins and catalyzes the conjugation of leukotriene A4 with glutathione to form leukotriene C4, a powerful mediator of allergic inflammation and anaphylaxis. Structural information on this class of proteins would be highly useful for rational drug design. Here, we report the expression, purification, and crystallization of recombinant LTC4S from rat. The enzyme was expressed as an N-terminal hexa-histidine-tagged fusion protein in Pichia pastoris and purified with two steps of affinity chromatography on Ni–Sepharose and S-hexyl-glutathione agarose, followed by gel filtration. From 1 l culture, we obtained 0.5–1 mg of apparently homogeneous protein with a specific LTC4S activity ranging between 36 and 49 μmol/mg/min. A small-scale screen identified dodecyl maltoside as a useful detergent for protein extraction and yielded a highly active protein. When tested separately in crystallization trials of the purified LTC4S, six out of seven detergents from all the maltoside family yielded diffracting crystals with the highest resolution at ∼6 Å. Hence, our approach holds promise for solving the structure of rat LTC4S and other members of the MAPEG family of integral membrane proteins.