Brazzolotto_2012_Febs.J_279_2905

Butyrylcholinesterase is a serine hydrolase present in all mammalian tissues. It can accommodate larger substrates or inhibitors than acetylcholinesterase, the enzyme responsible for hydrolysis of the neurotransmitter acetylcholine in the central nervous system and neuromuscular junctions. AChE is the specific target of organophosphorous pesticides and warfare nerve agents, while BChE is their stoichiometric bioscavenger. Conversion of BChE into a catalytic bioscavenger by rational design or designing reactivators specific to BChE required structural data obtained with a recombinant low-glycosylated human BChE expressed in Chinese hamster ovary cells. This expression system yields about 1 mg of pure enzyme per liter of cell culture. Here, we report an improved expression system with 4-fold higher yield for truncated human BChE with all glycosylation sites present using insect cells. We developed a fast purification protocol of the recombinant protein using a huprine-based affinity chromatography superior to the classical procainamide-based affinity. The purified BChE crystallized in different conditions and space group than those for the recombinant low-glycosylated protein produced in Chinese hamster ovary cells. The crystals diffracted to 2.5 A. The overall monomer structure is similar to the low-glycosylated structure but for the presence of the additional glycans. Remarkably, the carboxylic acid molecule systematically bound to the catalytic serine in the low-glycosylated structure is also present in this new structure, despite the different expression system, purification protocol and crystallization conditions.