Interaction of C70 fullerene with the Kv1.2 potassium channel

Abstract

Fullerene C(70) is known to partition into lipid membranes and change their physical properties. Together with gallic acid (GA), C(70) induces cell contraction and cell death. How C(70) and GA-induced perturbations of lipid membranes affect cellular function and membrane protein activity is not understood, though. Meanwhile, fullerene is also known to interfere with the activity of potassium channel proteins, but the mechanisms of protein inhibition are not known. Here we consider the possibility that membrane protein function would be inhibited by C(70) and/or GA through direct contact or through lipid-mediated interactions. To this end, we use microsecond time scale atomistic simulations to explore (a) modifications of membrane properties in the presence of C(70) and/or GA, and (b) the possible conformational changes in Kv1.2, a voltage-gated potassium channel, upon exposure to C(70), or GA, or both. C(70) is found to have an observable effect on structural and elastic properties of protein-free membranes, while the effects of GA on the membrane are less evident. Fullerene–GA interaction is strong and affects significantly the partitioning of C(70) in the membrane, stabilizing C(70) in the aqueous phase. When Kv1.2 is exposed to the solutes, only small conformational changes are observed on the microsecond time scale – comparable to the fluctuations observed in the absence of any solute. Blocking of the channel entrance is not observed, as fullerene binds mainly to hydrophobic residues, both in the water-exposed loops and in the transmembrane helices. The tilt angle of transmembrane helices in the voltage-sensing domain appears to be affected by direct contact with fullerene, but a generic effect due to the small increase in membrane thickness might also play a role. A small rotation of the S3 and S4 helices in the voltage-sensing domain is noticed when C(70) is embedded in the membrane. The interpretation of the observed conformational changes is not straightforward due to the associated time scales, which are difficult to sample with state-of-the-art computing resources. We cannot exclude that both membrane-mediated interactions and specific protein–solute interactions affect the conformation of the protein.