Insights from P-Glycoprotein in-silico modelling

P-glycoprotein (P-gp) is the most representative member of the ABC transmembranar transporter superfamily, often implicated in the multidrug-resistance phenomenon (MDR) [1]. Several models have been proposed for the efflux mechanism, namely the hydrophobic pore, the flipase model and, more recently, the hydrophobic vacuum-cleaner model.

Using the bacterial transporters Sav1866, BtuCD or MsbA, several homology models have been constructed. However, the majority proved to be inaccurate due to errors introduced during the homology process, originating misleading results. The recently published crystallographic structure of the murine P-glycoprotein [2] constitutes a more suitable working model. However, a linker known to regulate substract's specificity and to be involved in the conformational changes that accompanies ATP hydrolysis was not mapped [3].

Starting with the murine P-gp crystallographic structure, we built a system comprising a correctly protonated P-gp structure inserted in a lipid bilayer inside a molecular dynamics simulation box with respective counter-ions and waters to solvate all the system. Variations on this system were studied that allowed examining the influence of the linker and lipid type on the P-gp structure stability. The lipid environment and bilayer rigidity was also tested by studying systems with and without cholesterol. Different force field parameterizations were used for quality assessment.

The molecular dynamics systems were simulated for tens of nanoseconds using the GROMACS simulation package and the new insights gathered from the simulations namely dynamic and static properties both from P-gp and lipids will be presented and discussed.

Acknowledgement: This study was supported by FCT, Portugal (project PTDC/QUI-QUI/099815/2008)

References: 1. Juliano R et al. (1976) Biochimica et Biophysica Acta 455: 152–162

2. Aller S. et al. (2009) Science 323: 1718–1722

3. Sato T et al. (2009) FEBS 276: 3504–3516