Structural basis of transfer between lipoproteins by cholesteryl ester transfer protein

Abstract

Human cholesteryl ester transfer protein (CETP) mediates the net transfer of cholesteryl ester mass from atheroprotective high-density lipoproteins to atherogenic low-density lipoproteins by an unknown mechanism. Delineating this mechanism would be an important step toward the rational design of new CETP inhibitors for treating cardiovascular diseases. Using EM, single-particle image processing and molecular dynamics simulation, we discovered that CETP bridges a ternary complex with its N-terminal β-barrel domain penetrating into high-density lipoproteins and its C-terminal domain interacting with low-density lipoprotein or very-low-density lipoprotein. In our mechanistic model, the CETP lipoprotein-interacting regions, which are highly mobile, form pores that connect to a hydrophobic central cavity, thereby forming a tunnel for transfer of neutral lipids from donor to acceptor lipoproteins. These new insights into CETP transfer provide a molecular basis for analyzing mechanisms for CETP inhibition.

Structural Plasticity of Cholesteryl Ester Transfer Protein Assists the Lipid Transfer Activity

“…6 shows, the CETP tunnel significantly elongates from the crystal conformation and stabilized to an extended length of ϳ95 Å during the final 500-ns simulation time when CE N was linear. This finding is consistent with the recent EM structure of CETP bound to HDL and LDL, which suggested a more continuous hydrophobic tunnel, compared with the shorter 60-Å central cavity observed in the CETP crystal structure (21). We speculate that the constricted tunnel found in the CETP crystal structure is a consequence of the crystal packing effects, as was also observed in the crystal structures of other proteins (e.g.…”

“…Interestingly, one of the CEs in the hydrophobic tunnel was in the bent conformation, whereas the second CE molecule was in the linear conformation. Recent cryopositive staining EM and optimized negative-staining electron microscopy (OpNS-EM) protocols combined with CETP C terminus-specific polyclonal antibody studies have suggested that CETP penetrates its C-terminal ␤-barrel domain into LDL or VLDL and its N-terminal ␤-barrel domain into HDL to form a ternary complex (21). Further, it was suggested that the aforementioned long continuous hydrophobic tunnel that traverses along the long axis of CETP can connect to the core of HDL and LDL simultaneously to facilitate the transfer of CEs and TGs between the lipoproteins.…”

“…Given the complexity of lipid metabolism and the pivotal role of CETP in the process, understanding CETP structure, CETP inhibition, and the mechanism by which CETP transfers neutral lipids is of prime importance. The last decade, therefore, has seen the employment of sophisticated techniques, like cryo-EM (21,22), x-ray (23,24), and MD simulations (25)(26)(27)(28) on this front. Nevertheless, the story of CETP remains far from complete.…”

Recent advances in physiological lipoprotein metabolism

“…Electron microscopy show virtually no CETP complexes bridging two HDLs, LDLs or VLDLs, implying CETP domain specificity for HDL (N-terminal) and LDL and VLDL (C-terminal) The co-existence of ternary complexes of HDL-CETP-LDL and HDL-CETP-VLDL and lipid transfer are consistent with the mechanistic model of cholesterol ester transfer through a tunnel within CETP, though at this point the continuous hydrophobic tunnel between the distal portions of the Nand C-terminal domains of CETP is hypothetical. Changes in hydrophobicity along the central cavity are suggested as one of the dynamic forces which favor a cholesteryl ester N-to C-terminus transfer [255]. Both CETP structure and circulating molar concentrations of lipoproteins are thought to contribute to CETPs physiological preference for HDL [256].…”

Cholesteryl ester transfer protein inhibition as a strategy to reduce cardiovascular risk

“…1 ) ( 12,18,19 ), and ii ) a tunnel mechanism in which CETP bridges two lipoproteins to form a ternary complex, with lipids fl owing from the donor to acceptor lipoprotein through the CETP molecule ( Fig. 2 ) (20)(21)(22). Proposed shuttle mechanism for cholesteryl ester transfer by CETP.…”