A molecular dynamics simulation study to understand the effect of cholesterol and tissue factor palmitoylation on...

Tissue factor (TF), a transmembrane glycoprotein, plays a profound role in the formation of the tissue factor-factor VIIa (TF-FVIIa) complex that initiates factor Xa (FXa) generation followed by thrombin activation and clot formation. Previous reports suggest that TF-FVIIa coagulant activity at the cell surface may be affected by various processes, including changes in cholesterol content and posttranslational modifications of TF. Numerous studies were conducted but yielded inconclusive results about the effect of cholesterol on TF expression.

The present study aimed to understand how cholesterol affects structural modulations on the tissue factor-factor VIIa-factor Xa ternary complex (TF-FVIIa-FXa). Additionally, we aimed to illustrate the effect of palmitoylation on the Cys245 residue of TF and understand its structural implications on the TF-FVIIa-FXa.

We set up the following 4 systems in different lipid environments: TF-FVIIa-FXa in POPC:POPS (CS), TF-FVIIa-FXa in POPC:POPS:CHOL (CSL), Palmitoylated TF-FVIIa-FXa in POPC:POPS:CHOL (CSLP), and Palmitoylated TF-FVIIa-FXa in POPC:CHOL (CLP), respectively, and subjected them to molecular dynamics simulation.

Hydrogen-bond and contact probability analysis were performed between various important domains of TF-FVIIa-FXa and notable novel interactions: Asn93^FVIIa:L-Lys48^TF, Arg178^FVIIa:H-Asp95^FXa:B, Lys20^FVIIa:H-Glu193^FXa:A, Arg178^FVIIa:H-Asp97^FXa:B, and Arg153^FVIIa:H-Gln135^FXa:B have been reported. The protein stability study implies that the CS and CLP systems are thermodynamically less stable than CSL and CSLP systems.

Analysis of molecular dynamic simulation data suggests that the presence of cholesterol and palmitoylation may contribute to structural rigidity, stability, and compactness of key domains of TF-FVIIa-FXa by augmenting protein-protein and protein-lipid interactions.