MODIFICATION OF THE N-TERMINAL CYSTEINE OF PLASMA CHOLESTERYL ESTER TRANSFER PROTEIN SELECTIVELY INHIBITS TRIGLYCERIDE TRANSFER ACTIVITY

An invariant cysteine residue is found at the N-terminus of cholestery l eater transfer protein (CETP) isolated from plasma of humans, rabbit s and cynomolgus monkeys. We previously reported the expression of rec ombinant rabbit cholesteryl ester transfer protein in yeast (Kotake et al., J. Lipid Res. 1996; 37: 599-605). The recombinant CETP secreted into the medium contains an altered N-terminal sequence but was fully capable of facilitating both cholesteryl eater (CE) and triglyceride ( TG) transfer between lipoproteins. We investigated the importance of t he conserved N-terminal cysteine of plasma CETP in the lipid transfer activity by chemical modification of the free sulfhydryl groups of the recombinant CETP and CETP from human and rabbit plasma. The unmodifie d forms of these CETPs had similar specific activities of CE and TG tr ansfer. Neither 5,5'-dithiobis-(2-nitrobenzoate) nor N-ethyl maleimide altered the lipid transfer activity. In contrast, p-chloro-mercuriphe nyl sulfonate selectively inhibited the TG transfer activity of both h uman and rabbit plasma CETP. The TG and CE transfer activities of the recombinant CETP, which lacks the N-terminal cysteine residue, was not affected. These results demonstrate that the N-terminal cysteine resi due of both human and rabbit plasma CETP is free and is likely to be i nvolved in the construction of a critical part of the active site of C ETP that can determine the selectivity of the lipid molecule for the t ransfer reaction. (C) 1997 Elsevier Science B.V.