CETP and exchangeable apoproteins: Common features in lipid binding activity

In order to define the active domain for lipid binding in CETP (cholesteryl ester transfer protein), our study discusses some fundamental physicochemical properties of this molecule such as hydrophobic moment, protein active surface and helix amphipathicity, in comparison to the properties reported for a series of apoproteins including apoAI, apoAII, apoCI, CII, CIII and apoE. Our study suggests that CETP corresponds to a protein with an active surface slightly lower than the one calculated for the exchangeable apoproteins AI, AII, CI, CII, CIII and E. Arrays type (i, i + 3) and (i, i + 4) were found in the region associated to lipid binding in these apoproteins. Seven such arrays located in the amphipathic a-helices of CETP are also suggested to contribute to the overall lipid binding activity as a consequence of a-helix stability. It is proposed that for lipid binding to occur in both types of molecules, the possibility of a conformational specificity given by a redundant stereochemical code can be actively operating.