Bennati, Marina, Prof. Dr.

1995- PhD (Physics) University of Stuttgart

1996-1999 DFG Postdoctoral fellow, MIT Cambridge (USA)

1999-2001 MIT sponsored research staff associate

2002-2006 Lecturer and research scientist, University of Frankfurt

2007- Independent research group leader, Electron Paramagnetic Resonance
Spectroscopy, MPI for Biophysical Chemistry, Göttingen

Homepage Department/Research Group

http://www.mpibpc.mpg.de/english/research/ags/bennati/



Major research interest

EPR Spectroscopy for Biomolecular Structure

Our research focuses on the investigation of paramagnetic centers in biological systems with electron paramagnetic resonance (EPR) spectroscopy. In biological processes, paramagnetic centers are encountered as metal ions or clusters, amino acid radicals cofactors in electron transfer or catalytic reactions or can be inserted in diamagnetic proteins in form of spin labels. The recent advent of high-field EPR in combination with pulsed techniques, has substantially increased the available sensitivity and resolution, allowing us to explore biological systems close to their physiological conditions.

Local structure at atomic resolution can be achieved by detecting the interaction of electron spins with surrounding magnetic nuclei in electron nuclear double resonance (ENDOR). This method permits one to determine the distance as well as the orientation of nuclear spins with respect to a paramagnetic center. The figure illustrates nuclei that were detected in a 95 GHz ENDOR experiment to elucidate the structure of the active site in a p21ras-Mn-GDP complex.

Adapted from Bennati et al. (2006) Biochemistry 45: 42

Distances and orientations in protein complexes by high-field pulse EPR
Pulse EPR spectroscopy can be used to detect the interaction between two unpaired electron spins. These techniques enable long-range distance measurements on the order of 2 up to 8 nm and can give information on the assembly of protein complexes or tertiary structures in large proteins or enzymes at concentrations as low as 10 - 20 μM. Experiments performed at high magnetic fields contain also information about the relative orientations of two paramagnetic centers.

The RNR-R2 dimer from mouse. Structure of the tyrosyl biradical determined in high-field PELDOR, as defined by the projection angles θij between the g-tensor principal axes and the dipolar distance vector r at each radical site. Adapted from V. Denysenkov et al. (2008) Angewandte Chemie 147: 1224

Studies of enzymatic mechanisms: Ribonucleotide reductase
RNRs catalyse the reduction of nucleotide into deoxynucleotide in all living cells, the rate-determining step in DNA biosynthesis. The class I enzymes are composed of two subunits, R1 and R2. The R2 subunit contains the essential diferric cluster-tyrosyl radical cofactor and R1 is the site of conversion of nucleoside diphosphates to 2’-deoxynucleoside diphosphates. In collaboration with the group of J. Stubbe (MIT) we are investigating the mechanism of the long-range electron transfer between R2 and R1 using EPR long-range distance measurements in the active enzyme by freeze quenching the intermediate states. We have measured the distance between the Y•s in R2 as well as the cross distance between R1 and R2 (Figure 3).

Predicted diagonal and linear distances by the docking model (black) and measured diagonal distances obtained by PELDOR (blue) projected onto the docking model of E. coli Ribonucleotide Reductase. Adapted from M. R. Seyedsayamdost, M. Bennati et al. (2007) J. Am. Chem. Soc. 129: 15748

Selected recent publications

• Denysenkov V, Prisner T, Stubbe J, Bennati M (2006) High-field pulsed electron-electron double resonance spectroscopy to determine the orientation of the tyrosyl radicals in ribonucleotide reductase. Proc Natl Acad Sci USA 103, 13389


• Bennati M, Prisner T (2005) New developments in high field EPR with applications in structural biology. Rep Prog Phys 68, 411


• Bennati B, Lendzian F, Schmittle M, Zipse H (2005) Spectroscopic and theoretical approaches to study radical reactions in ribonucleotide reductase. Biol Chem 386, 1007


• Bennati B, Robblee JH, Mugnaini V, Stubbe J, Freed JH, Borbat P (2005) EPR distance measurements support a model for long-range radical initiation in E.coli ribonucleotide reductase. J Am Chem Soc 127, 15014


• Bennati M, Weiden N, Dinse KP, Hedderich R (2004) 57Fe ENDOR spectroscopy on the 4Fe4S cluster directly involved in substrate reduction in heterodisulfide reductase. J Am Chem Soc 128, 8379