Insights into the Tunnel Mechanism of Cholesteryl Ester Transfer Protein through All-atom Molecular Dynamics Simulations

Abstract

Cholesteryl ester transfer protein (CETP) mediates cholesteryl ester (CE) transfer from the atheroprotective high density lipoprotein (HDL) cholesterol to the atherogenic low density lipoprotein cholesterol. In the past decade, this property has driven the development of CETP inhibitors, which have been evaluated in large scale clinical trials for treating cardiovascular diseases. Despite the pharmacological interest, little is known about the fundamental mechanism of CETP in CE transfer. Recent electron microscopy (EM) experiments have suggested a tunnel mechanism, and molecular dynamics simulations have shown that the flexible N-terminal distal end of CETP penetrates into the HDL surface and takes up a CE molecule through an open pore. However, it is not known whether a CE molecule can completely transfer through an entire CETP molecule. Here, we used all-atom molecular dynamics simulations to evaluate this possibility. The results showed that a hydrophobic tunnel inside CETP is sufficient to allow a CE molecule to completely transfer through the entire CETP within a predicted transfer time and at a rate comparable with those obtained through physiological measurements. Analyses of the detailed interactions revealed several residues that might be critical for CETP function, which may provide important clues for the effective development of CETP inhibitors and treatment of cardiovascular diseases.

Role of glycans in cholesteryl ester transfer protein revealed by molecular dynamics simulation

“…The tunnel mechanism suggests a hydrophobic tunnel for neutral lipid exchanging among different lipoprotein fractions (ie HDL‐CETP‐LDL), which is supported by EM images and MD simulations . Our results show that Glycan88 enhances flexibility, and increases both hydrophobic and hydrophilic SASA of the N‐terminal of CETP, as well as allows CETP adopt a more stretched conformation.…”

“…Further down, the secondary structure of His25 converted into turn‐structure after ∼600 ns in the CETP‐G system, and the secondary structure of Glu26 converted into random coil after ∼600 ns. To be noted, there was a local high‐energy barrier including Leu23 when CEs pass through the tunneling . Thus, the glycans may promote the CEs transfer through breaking the alpha‐secondary structure of Pro18 to Ile31, and consequently allow CETP to adopt a more stretched conformation with higher hydrophobic, hydrophilic SASA, and flexibility in N‐terminal domain.…”

“…20 Furthermore, molecular dynamics (MD) simulations showed that a hydrophobic tunneling inside CETP-C is sufficient to allow a CE molecule to completely transfer through the entire CETP. 10,12 These results strongly suggest a tunneling mechanism, in which the cavities of CETP form a continuous tunneling that mediates the CE-TG transfer. 21 However, the driving force for CEs passing through the hydrophobic tunneling is still unclear, and the ternary tunneling complex (ie HDL-CETP-LDL) seems not to be the mechanistic prerequisite for the CETP function, revealed by immuno-transmission electron microscopy (TEM) images of variety binary complexes CETP-HDL and CETP-LDL.…”

“…More recent electron microscopy (EM) images revealed that the N‐terminal of CETP‐C penetrates the HDL surface and core (∼50 Å), whereas the C‐terminal penetrates the LDL or VLDL only ∼25 Å . Furthermore, molecular dynamics (MD) simulations showed that a hydrophobic tunneling inside CETP‐C is sufficient to allow a CE molecule to completely transfer through the entire CETP . These results strongly suggest a tunneling mechanism, in which the cavities of CETP form a continuous tunneling that mediates the CE‐TG transfer .…”

“…While plasma CETP has 4 potential N‐linked glycosylation sites (CETP‐G), which play an important role in the heteroexchange of CEs and TGs between lipoproteins . Up to now, most studies on CETP have only focused on the nascent structure of CETP (CETP‐N, mutated residues were reversed) and CETP‐C . Thus, little is known about the detailed structural information of CETP‐G and effect of glycans on the structure and function of CETP, as well as the accompanying modulation of CEs transfer.…”