Open and closed states of Candida Antarctica lipase B: Protonation and the mechanism of interfacial activation

Abstract Lipases (EC 3.1.1.3) are ubiquitous hydrolases for the carboxyl ester bond of water-insoluble substrates, such as triacylglycerols, phospholipids, and other insoluble sub- strates, acting in aqueous as well as in low-water media, thus being of considerable physiological significance with high in- terest also for their industrial applications. The hydrolysis reaction follows a two-step mechanism, or “interfacial activa- tion,” with adsorption of the enzyme to a heterogeneous in- terface and subsequent enhancement of the lipolytic activity. Among lipases, Candida antarctica lipase B (CALB) has never shown any significant interfacial activation, and a closed con- formation of CALB has never been reported, leading to the conclusion that its behavior was due to the absence of a lid regulating the access to the active site. The lid open and closed conformations and their protonation states are ob- served in the crystal structure of CALB at 0.91 Å resolution. Having the open and closed states at atomic resolution allows relating protonation to the conformation, indicating the role of Asp145 and Lys290 in the conformation alteration. The findings explain the lack of interfacial activation of CALB and offer new elements to elucidate this mechanism, with the consequent implications for the catalytic properties and clas- sification of lipases.—Stauch, B., S. J. Fisher, and M. Cianci. Open and closed states of Candida antarctica lipase B: proton- ation and the mechanism of interfacial activation. J. Lipid Res. 2015. 56: 2348–2358.