Dominant conformation of valsartan in sodium dodecyl sulfate micelle environment

The interaction of valsartan (VST), a novel antihypertensive drug, with sodium dodecyl sulfate (SDS) micelles has been investigated using Nuclear Magnetic Resonance (NMR) spectroscopy and Molecular Dynamics (MD) simulation. VST has two conformations in solution, exchanging slowly on the NMR time scale via the trans/cis (conformer A/B) isomerization of the amide bond. It is suggested that drugs in the sartan class incorporate and diffuse into biological membranes before they interact with AT(1) receptors. SDS is used to mimic the membrane environment to characterize two VST conformers. (1)H NMR chemical shift analysis, proton relaxation rates, and self-diffusion coefficient measurements suggest that conformer A has a higher binding affinity to SDS and is the dominant conformer distributed in the SDS micelles. The location of VST in the micelles is determined by NOE measurements and by the MD simulation, showing that the butyl chain and biphenyl groups of VST interact with the alkyl group of SDS through hydrophobic interactions. Preferable binding free energy is found for conformer A by the MD simulation, which demonstrates that the relatively concentrated hydrophobic surface of conformer A is responsible for its higher affinity to the micelles. Our results are in good agreement with a recent simulation of VST bound onto the AT(1) receptor by Potamitis et. al (J. Chem. Inf. Model. 2009) who demonstrate that conformer A (trans conformation in their definition) is the one binding to the receptor. The results presented in our study suggest that the biological membrane plays an essential role in stabilization of the active state of VST. Thus, understanding the interactions between the sartan drugs and the membrane environment should facilitate the studies of the functional mechanism of these compounds with their receptor and provide insight on the development of new approaches for drug discovery.