A molecular dynamics study of Fe2S2 putidaredoxin: multiple conformations of the C-terminal region.

Putidaredoxin (Pdx) plays an essential role as an electron donor and effector in the biochemical cycle involving cytochrome P450cam. Only recently has an NMR-derived structure for this protein been published, but because of the presence of a paramagnetic Fe2S2 center, the NMR assignment could not be completed for residues within a region of 8 A around the active site. That region was modeled by homology with a related protein. The structural refinement for those experiments was done in vacuum, without the use of electrostatic terms in the force field. The present manuscript will describe and discuss a series of long-time, unrestrained, solution molecular dynamic runs for this system. Results will be presented that construct a molecular-level picture that rationalizes experimental results concerning the conformation and mobility of the C-terminal residue Trp106. At least two different conformers are found for this residue during the simulations. The time scale for interconversion between them is found to be in the subnanosecond regime. The results presented here open the possibility for studying binding and electron transfer between Pdx and P450cam, in a framework that allows for dynamical information to be used during the computational process, instead of the single structures deposited on the protein data base.