Trapping of different lipase conformers in water-restricted environments

Based on a recently reported strategy to rationally activate lipolytic enzymes for use in nonaqueous media [Mingarro, I., et al. (1995) Proc. Natl. Acad. Sci. U.S.A. 92, 3308-3312], we compared the behavior in water-restricted environments of activated vs nonactivated forms of different lipases toward their natural substrates, triacylglycerols. To this end, nine lipases from varied origins (mammalian, fungal, and bacterial) were assayed using simple acidolyses as nonaqueous model reactions. The experimental results for several (though not all) lipases, discussed in the light of current structural and functional information, were collectively consistent with a model where, depending on the "history" of sample preparation, basically two different conformers (open and closed) of the lipase can be trapped (and assayed) in the nonaqueous medium. In particular, for a few prototypic lipases investigated in more detail, the following were shown: (i) the activation strategy permitted them to rationally overcome their reported reluctance to convert saturated, long-chain triglycerides, providing quantifiable nonaqueous rate accelerations of up to 3 orders of magnitude; (ii) the activated conformer exhibited a markedly higher ability than its nonactivated counterpart to bind a ligand (nonhydrolyzable phospholipid) in the nonaqueous medium; and (iii) a clearly distinct selectivity profile toward the substrate chain length was obtained for either conformer.