The simulation of the electronic circular dichroism (CD) spectroscopy of the oxidised form of the blue copper proteins plastocyanin and cucumber basic protein will be discussed. Using excitation energies and transition strengths computed within the framework of multi reference configuration interaction (MRCI), it is shown that the resulting spectra based the coordinates from the crystal structure or a single structure optimised using quantum mechanics/molecular mechanics (QM/MM) or ligand field molecular mechanics (LFMM) are qualitatively incorrect. In particular, the rotational strength of the ligand to metal charge transfer band is predicted to be too small or have the incorrect sign. By considering calculations on active site models with modified structures it is shown that the intensity of this band is sensitive to the non-planarity of the histidine and cysteine ligands coordinated to copper. Calculation of the ultraviolet absorption and CD spectra based upon averaging over many structures drawn from a LFMM molecular dynamics simulation are in good agreement with experiment, and superior to analogous calculations based upon structures from a classical molecular dynamics simulation. This indicates that structural averaging is important for simulating the CD spectroscopy of these systems, and that the LFMM force field provides an accurate description of the molecular dynamics of these proteins.

Simulation of the structure and spectroscopy of blue copper proteins

251st National Meeting (2016)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.