Sulfur K-Edge XAS Studies of the Effect of DNA Binding on the [Fe_4S_4] Site in EndoIII and MutY
S K-edge X-ray absorption spectroscopy (XAS) was used to study the [Fe_4S_4] clusters in the DNA repair glycosylases EndoIII and MutY to evaluate the effects of DNA binding and solvation on Fe–S bond covalencies (i.e., the amount of S 3p character mixed into the Fe 3d valence orbitals). Increased covalencies in both iron–thiolate and iron–sulfide bonds would stabilize the oxidized state of the [Fe_4S_4] clusters. The results are compared to those on previously studied [Fe_4S_4] model complexes, ferredoxin (Fd), and to new data on high-potential iron–sulfur protein (HiPIP). A limited decrease in covalency is observed upon removal of solvent water from EndoIII and MutY, opposite to the significant increase observed for Fd, where the [Fe_4S_4] cluster is solvent exposed. Importantly, in EndoIII and MutY, a large increase in covalency is observed upon DNA binding, which is due to the effect of its negative charge on the iron–sulfur bonds. In EndoIII, this change in covalency can be quantified and makes a significant contribution to the observed decrease in reduction potential found experimentally in DNA repair proteins, enabling their HiPIP-like redox behavior.
© 2017 American Chemical Society. Received: April 19, 2017. Published: July 18, 2017. This work was supported by NIH grants (GM040392, E.I.S.; GM103393, K.O.H.; GM120087 J.K.B.; CA069875 S.S.D.). J.K.B. also thanks the Moore Foundation. A.R.A. was supported by the National Institute of Aging of the NIH on a predoctoral NRSA (F31AG040954). Portions of this research were carried out at the Stanford Synchrotron Radiation Lightsource (SSRL), a Directorate of SLAC National Accelerator Laboratory and an Office of Science User Facility operated for the U.S. Department of Energy (DOE) Office of Science by Stanford University. The SSRL Structural Molecular Biology Program is supported by the DOE Office of Biological and Environmental Research and by the National Institutes of Health, National Institute of General Medical Sciences (P41GM103393). The authors declare no competing financial interest.
Accepted Version - nihms894225.pdf
Supplemental Material - ja7b03966_si_001.pdf