What is the Real Nature of Ferrous Soybean Lipoxygenase-1? A New Two-Conformation Model Based on Combined ONIOM(DFT:MM) and Multireference Configuration Interaction Characterization

The geometric and spectral features of the ferrous resting state of soybean. lipoxygenase-1 (SLO-1) have remained puzzling. We have theoretically characterized ferrous SLO-1 by means of the ONIOM(DFT:MM). TDDFT, and CASSCF/SORCI methods, taking explicitly into account the effect of the protein environment. Two conformations found theoretically in this study, Conf-A and Conf-B, have almost equal stability but have quite different geometries, with short and long Fe-O-694 distances, respectively While neither of the geometries agreed well with the crystal structure of the enzyme, an averaged geometry showed excellent agreement. Therefore, we propose that the crystal structure reflects a mixture of these two conformations. The calculated circular dichroism (CD) spectra for Conf-A and Conf-B were found to agree well with the two experimental spectra obtained previously for six coordinate and five coordinate forms of ferrods SLO-1, respectively.