[초청강연] Modulation of the biophysical properties of the Rieske iron sulfur protein in the bc1 complex

The first electron / proton transfer from the substrate, hydroquinone species to the oxidized Rieske-type iron sulfur protein (ISP) is the rate-limiting step in the overall reaction of the bc1 complex, which is governed by the biophysical properties of this subunit. The electronegative atoms (O, N, and S) in the side chains and the backbone of the surrounding amino acids have been reported as the determinants of the unique biophysical properties of ISP in the bc1 complex, a higher midpoint potential (Em) and a lower pK. We have constructed most of the possible mutant strains at the S154, Y156, L132, and G133 positions, and for those which assembly an intact ISP, we are determining the X-ray crystallographic structures. We are also making substantial progress in characterization of the local protein environment by spectroscopy (ESEEM, HYSCORE, RR, FTIR, NMR and XANES approaches are being used).The biophysical properties of the mutant ISPs were evaluated by means of circular dichroism (CD) spectroscopy, protein film voltammetry (PFV), Qo-site class II inhibitor resistance, and pre-steady state kinetic measurements. The resulting values were used in a detailed Marcus-Brønsted analysis to model the effect of the mutations on changes in electron transfer characteristics. This study confirms that the H-bonds to the [2Fe-2S] cluster or its ligands are important determinants of the electrochemical characteristics of the ISP. This is likely related to the electron affinity of the oxygen atom and the geometry of the H-bonding network surrounding the cluster.