Impact of Cholesterol on the Stability of Monomeric and Dimeric Forms of the Translocator Protein TSPO: a Molecular Simulation Study

Abstract

The translocator protein (TSPO) is a transmembrane protein present in the three domains of life. Its functional quaternary structure consists of one or more subunits. In mouse, the dimer-to-monomer equilibrium is shifted in vitro towards the monomer by adding cholesterol, a natural component of mammalian membranes. Here, we present a coarse-grained molecular dynamics study on the mouse protein in the presence of a physiological content and of an excess of cholesterol. The latter turns out to weaken the interfaces of the dimer by clusterizing mostly at the inter-monomeric space and pushing the contact residues apart. It also increases the compactness and the rigidity of the monomer. These two factors might play a role for the experimentally observed incremented stability of the monomeric form with increased content of cholesterol. Comparison with simulations on bacterial proteins suggests that the effect of cholesterol is much less pronounced for the latter than for the mouse protein.

The Interplay of Cholesterol and Ligand Binding in hTSPO from Classical Molecular Dynamics Simulations

“…Indeed, the latter is currently the best template choice in comparative modeling of mammalian TSPOs [ 40 , 41 ] for the following reasons: (i) the structural folds of the TSPOs on passing from the bacterial to the mammalian proteins are conserved [ 34 , 35 , 36 ]; (ii) the NMR Mo TSPO structure is affected by the ionic detergents used for the purification during the measurements [ 36 ]; as a result, the positions of highly conserved amino acids and of the transmembrane helices are altered [ 40 ]; (iii) the Rs TSPO crystal structure was resolved at a relatively good resolution (1.8 Å).…”

“…Bacterial and mouse TSPO can exist as monomers, dimers, and other oligomers as shown by experiments [ 34 , 35 , 37 , 38 ]. Different computational molecular modeling studies were carried out to further shed light on the dimerization of mouse and bacterial TSPO and on how ligands (small chemical compounds, porphyrin, cholesterol) interact with dimers or influence their stability [ 39 , 40 , 41 , 42 ]. In contrast, the oligomerization state of h TSPO has not been established.…”

CGMD Platform: Integrated Web Servers for the Preparation, Running, and Analysis of Coarse-Grained Molecular Dynamics Simulations

“…TSPO is an 18 KDa membrane protein conserved across the three domains of life [ 36 ] with a vast spectrum of roles ranging from an environmental sensor to a functional bioregulator of apoptosis, autophagy, inflammation, along with cholesterol and porphyrin transport [ 37 ]. Recently, we presented a CGMD study of this receptor aimed at the characterization of the impact of cholesterol in the formation of multimeric assemblies [ 38 ]. In this paper, we claimed that cholesterol affects the size and rigidity of the bacterial translocator proteins to a lesser extent than the mammalian protein.…”

“…Additional plots provided on the analysis page offer tools to assess the behavior of the simulation, which were stable in all the ensembles. Indeed, taking all the analyses together, the user has a system that is prepared to be run in a similar fashion to the one in [ 38 ]. During and after the simulation, the users are constantly informed of the status of their calculation through a progress bar positioned at the top of each analysis page, which is always accessible.…”