Validation of the mechanism of cholesterol binding by StAR using short molecular dynamics simulations.
We previously proposed an original two-state cholesterol binding mechanism by StAR, in which the C-terminal alpha-helix of StAR gates the access of cholesterol to its binding site cavity. This cavity, which can accommodate one cholesterol molecule, was proposed to promote the reversible unfolding of the C-terminal alpha-helix and allow for the entry and dissociation of cholesterol. In our molecular model of the cholesterol-StAR complex, the hydrophobic moiety of cholesterol interacts with hydrophobic amino acid side-chains located in the C-terminal alpha-helix and at the bottom of the cavity. In this study, we present a structural in silico analysis of StAR. Molecular dynamics simulations showed that point mutations of Phe(267), Leu(271) or Leu(275) at the alpha-helix 4 increased the gyration radius (more flexibility) of the protein's structure, whereas the salt bridge double mutant E169M/R188M showed a decrease in flexibility (more compactness). Also, in the latter case, an interaction between Met(169) and Phe(267) disrupted the hydrophobic cavity, rendering it impervious to ligand binding. These obtained results are in agreement with previous in vitro experiments, and provide further validation of the two-state binding mode of action.
Barbar
Elie
E
Département de Biochimie, Faculté de médecine et des sciences de la santé, Université de Sherbrooke, Sherbrooke, Québec, Canada J1H 5N4.
Lavigne
Pierre
P
Lehoux
Jean-Guy
JG
D002784:Cholesterol / Q000378:metabolism*; D003198:Computer Simulation; D006801:Humans; D008958:Models, Molecular; D050505:Mutant Proteins / Q000737:chemistry / Q000378:metabolism; D010750:Phosphoproteins / Q000737:chemistry* / Q000378:metabolism*; D017433:Protein Structure, Secondary; D015203:Reproducibility of Results; D000098682:Steroidogenic Acute Regulatory Protein
D050505:Mutant Proteins; D010750:Phosphoproteins; D000098682:Steroidogenic Acute Regulatory Protein; D002784:Cholesterol