Modelling of third cytoplasmic loop of bovine rhodopsin by multicanonical molecular dynamics.

The third cytoplasmic loop (C3) of bovine rhodopsin (Rh) is an important site for its interaction with G-protein transducin. The tertiary structure of Rh was determined by X-ray crystallography, although the local conformation around the C3 loop (residues: 236-240) was not visible in electron density maps. We constructed a canonical conformation ensemble at 310 K for the C3 loop (residues: 227-244) using a multicanonical molecular dynamics simulation, and predicted several putative conformations. The conformation ensemble was classified by principal component analysis into several distinct structural clusters, some of which could provide the putative structural models of Rh and the activated state of Rh.