▎ 摘　　要

The fragment of viral protein R (Vpr), Vprl 3-33, plays an important role in regulating nuclear importing of HIV genes through channel formation in which it adopts a leucine-zipper-like alpha-helical conformation. A recent experimental study reported that helical Vprl 3-33 would transform to beta-sheet or random coil structures and aggregate on the surface of graphene or graphene oxide through hydrophobic interactions. Due to experimental limitations, however, there is still a considerable lack of understanding on the adsorption dynamics at the early stage of the conformational transition at water-graphene interface and the underlying driving force at molecular level. In this study, atomistic molecular dynamics simulations were used to explore the conformation transition phenomena. Vpr13-33 kept alpha-helical structure in solution, but changed to beta-sheet structure when strongly adsorbed onto graphene. Preferential adsorption of Vpr13-33 on graphene is dominated by hydrophobic interactions. The cluster analysis identified the most significant populated conformation and the early stage of structure conversion from a-helical to p-sheet was found, but the full beta-sheet propagation was not observed. Free energy landscape analysis further complemented the transformation analysis of peptide conformations. These findings are consistent with experimental results, and give a molecular level interpretation for the reduced cytotoxicity of Vpr13-33 to some extent upon graphene exposure. Meanwhile, this study provides some significant insights into the detailed mechanism of graphene-induced protein conformation transition. (C) 2016 Elsevier B.V. All rights reserved.