EPR characterization of mononuclear Mo/W enzymes

CARLOS D. BRONDINO

Sintra

Conferencia; Molybdenum & Tungsten Enzymes Conference; 2013

Departamento de Química, Universidad Nova de Lisboa

EPR Characterization of mononuclear Mo/W enzymes Carlos D. Brondino Departamento de Física, Facultad de Bioquímica y Ciencias Biológicas, Universidad Nacional del Litoral, Campus Universitario, S3000ZAA Santa Fe, Argentina e-mail brondino@fbcb.unl.edu.ar Molybdenum (Mo, atomic number 42) and Tungsten (W, atomic number 74) are second and third row transition elements, respectively, which are found in a mononuclear form in the active site of a diverse group of redox enzymes that generally catalyze oxygen atom transfer reactions. Mo- and W-enzymes catalyze reactions that imply a net exchange of two electrons between the enzyme active site and substrate, in which the metal ion (Mo or W) cycles between the redox states IV and VI. The two electrons involved in the course of both oxidative and reductive reactions flow through the protein by mean of an electron-transfer process mediated by an electron transfer chain. These chains may include distinct type of redox centers (usually situated ~ 10-20 Å away) connected by long chemical pathways which are thought to be involved in the above mentioned electron transfer processes [1]. The redox centers are paramagnetic in certain oxidation states and may present different relaxation properties. In addition, despite the long both distances and chemical paths, they can present weak magnetic couplings produced by spin-spin interactions such as dipolar and isotropic exchange, also known as superexchange interaction [2,3]. The fact that the redox centers may be paramagnetic has made the Electron Paramagnetic Resonance technique a valuable tool to characterize the electronic and relaxation properties of the metal ions and the nature and magnitude of the weak magnetic coupling among centers. Particularly, the analysis of the magnetic interaction between centers by EPR can be advantageously used to determine intercenter distances, to assign the EPR active centers with those of the structure, to evaluate magnitude and nature of the magnetic coupling, and the integrity of the electron transfer pathways in distinct protein conditions. We discuss some examples of mononuclear W- and Mo-enzymes characterized by EPR and how this spectroscopic technique can be used to obtain structural information that cannot be obtained with conventional structural techniques. [1] C. D. Brondino, M. G. Rivas, M. J. Romão, J. J. G. Moura, I. Moura, Accounts of Chemical Research, 2006, 39, 788-796. [2] N. I. Neuman, M. Perec, P. J. González, M. C. G. Passeggi, A. C. Rizzi, and C. D. Brondino Journal of Physical Chemistry A 2010, 114, 13069-13075. [3] P. J. González, G. I. Barrera, A. C. Rizzi, J. J. G. Moura, M. C. G. Passeggi, C. D. Brondino Journal of Inorganic Biochemistry 2009, 103, 1342-1346.