👤 Prasanna D Revanasiddappa

Cholesteryl ester transfer protein (CETP) plays a central role in plasma lipid transport, facilitating the exchange of neutral lipids, such as cholesteryl esters and triglycerides, between lipoproteins. Despite the existence of several lipid-carrying/binding proteins in the family, such as lipopolysaccharide-binding protein (LBP), bacterial permeability increasing protein (BPI), and phospholipid transfer protein (PLTP), the structural and mechanistic uniqueness of CETP in neutral lipid transfer remains underexplored. Moreover, the involvement of PLTP in neutral lipid transfer is still debated, with researchers presenting conflicting mechanisms. Therefore, this study investigates the distinct structural ability of CETP in mediating neutral lipid exchange compared to other lipid-binding proteins. The study also emphasizes that simple protein modeling based on templates may not guarantee structural integrity unless validated through simulations. To achieve our objectives, we employed molecular docking, comparative molecular dynamics simulations, structural analysis, and lipid-protein interaction profiling with representative neutral lipids. In addition, protein-lipid affinities, tunnel architecture, and conformational flexibility were examined to characterize CETP's unique features and evaluate the quality of the constructed model for PLTP. The results demonstrated that a tunnel-like hydrophobic channel in CETP facilitates bidirectional neutral lipid transfer, unlike the compartmentalized binding pockets observed in other proteins. In addition, the neutral lipids' unfavorable conformational orientation was not affected in PLTP, whereas the same unfavorable conformation is changed to a favorable conformation in CETP, making only the lipid-carrying protein have the ability to transfer the neutral lipids. In conclusion, our findings highlight that the CETP is a specialized neutral lipid carrier with a unique structural mechanism distinct from typical lipid-binding proteins. This comparative insight enhances understanding of the structural plasticity of each lipid-carrying protein and the reliability of the modeled structure. Show less

Cholesteryl Ester Transfer Protein (CETP) is a plasma glycoprotein that intervenes the reverse cholesterol transport (RCT) by equimolar exchange of Cholesteryl esters (CE) and Triglycerides (TGs) between anti-atherogenic High-Density Lipoproteins (HDLs) and pro-atherogenic Low-Density Lipoproteins (LDLs) resulting in the increased concentration of CEs in LDL. This is a potential cause for the formation of atherosclerotic plaques in blood vessels leading to fatality. Therefore, blocking the function of CETP has emerged as a novel strategy for suppressing atherosclerotic plaques. The crystal structure of CETP revealed two Cholesteryl esters (CEs) in the hydrophobic tunnel and two phospholipids (PLs) plugged on the concave surface. Previous lipid transfer assay experimental studies have shown a substantial reduction in the neutral lipid transfer in [R201S] and [I443W, V198W] mutants. However, the protein conformational arrangements due to the mutations present in the CETP system leading to a decrease in the transfer rate of neutral lipids is not explored. Thus, I explored the reason behind the decreased transfer rate in mutants using molecular dynamics (MD) simulations and free energy calculations. Resulting evidences show that R201S mutant induces unfavorable bending angle to CETP with a decreased binding efficiency between N-terminal phospholipid of CETP with S201. Also, an unfavorable conformation state of TGs is formed which makes them difficult to transfer across CETP. Likewise, [I443W, V198W] mutant induces unfavorable CE, TG, and bending angle conformation to CETP impeding neutral lipid transfer. Thus, my results provide sufficient insights on the causation for a decreased transfer rate as reported earlier. The detailed understanding obtained here could help in developing a new strategy in preventing the function of CETP by blocking the role of potential hot spot residues. Show less

Cholesteryl ester transfer protein (CETP) is a plasma glycoprotein that assists the transfer of cholesteryl esters (CEs) from antiatherogenic high-density lipoproteins (HDLs) to proatherogenic low-density lipoproteins (LDLs), initiating cholesterol plaques in the arteries. Consequently, inhibiting the activity of CETP is therefore being pursued as a novel strategy to reduce the risk of cardiovascular diseases (CVDs). The crystal structure of CETP has revealed the presence of two CEs running in the hydrophobic tunnel and two plugged-in phospholipids (PLs) near the concave surface. Other than previous animal models that rule out the PL transfer by CETP and PLs in providing the structural stability, the functional importance of bound phospholipids in CETP is not fully explored. Here, we employ a series of molecular dynamics (MD) simulations, steered molecular dynamics (SMD) simulations, and free energy calculations to unravel the effect of PLs on the functionality of the protein. Our results suggest that PLs play an important role in the transfer of neutral lipids by transforming the unfavorable bent conformation of CEs into a favorable linear conformation to facilitate the smooth transfer. The results also suggest that the making and breaking interactions of the hydrophobic tunnel residues with CEs with a combined effort from PLs are responsible for the transfer of CEs. Further, the findings demonstrate that the N-PL has a more pronounced effort on CE transfer than C-PL but efforts from both PLs are essential in the transfer. Thus, we propose that the functionally important PLs can be considered with potential research interest in targeting cardiovascular diseases. Show less

Cholesteryl ester transfer protein (CETP) facilitates the transfer of cholesteryl esters (CEs) from antiatherogenic high-density lipoproteins to proatherogenic low-density lipoproteins. Inhibition of CETP is therefore being pursued as a potential strategy to reduce cardiovascular risk. The crystal structure of CETP has revealed the existence of two neutral CEs and two charged phospholipids (PLs) in its hydrophobic tunnel. This is in direct contrast to the other lipid-binding proteins that contain only two bound lipids. Moreover, previous animal studies on mice showed no detectable PL-transfer activity of CETP. Thus, the role of bound PLs in CETP is completely unknown. Here, we employ molecular dynamics simulations and free-energy calculations to unravel the primary effects of bound PLs on CETP structure and dynamics and attempt to correlate the observed changes to its function. Our results suggest that the structure of CETP is elastic and can attain different conformations depending on the state of bound PLs. In solution, these PLs maintain CETP in a bent-untwisted conformation that can uphold neutral lipids in its core tunnel. Results also suggest that although both PLs complement each other in their action, the C-terminal PL (C-PL) imparts greater influence on CETP by virtue of its tighter binding. Our finding fits very well with the recent inhibitor-bound CETP crystal structure, where the inhibitor displaced the N-terminal PL for binding to CETP's central domain without disrupting the binding of C-PL. We speculate that the observed increased flexibility of CETP in the absence of PLs could play a crucial role in its binding with lipoproteins and subsequent lipid-transfer activity. Show less