Construction of a Variable Frequency Ka Band [26-40 GHz] Pulsed EPR Spectrometer for Multi-Dimensional ESEEM and ENDOR Studies of Metalloproteins

University Of Arizona, Tucson AZ

Investigators

Abstract

This award supports the development of a variable frequency pulsed Ka-band (26-40 GHz) EPR spectrometer for electron spin echo envelope modulation (ESEEM) and electron-nuclear double/triple resonance (ENDOR/ENQOR) studies of proteins containing paramagnetic metal atoms. Paramagnetic metal centers in biomolecules are exquisitely sensitive "beacons", whose magnetic coupling to nearby magnetic nuclei reveal the immediate surroundings of the metal atom and can thereby provide detailed information about catalytic reaction pathways. Ligands with coordinated O, N, or S atoms play crucial roles in the paramagnetic metal centers of many biomolecules. The hardware and software to be developed will enable powerful multi-dimensional pulsed EPR methods to be extended to the investigation of nearby magnetic nuclei such as 17O and 33S. In addition, this new instrument will substantially simplify the analysis of coupling with 14N atoms. The hyperfine interaction (hfi) and nuclear quadrupole (nqi) parameters obtained for these atoms will provide direct insight into their paramagetic metal centers. The project includes construction of the instrument, and development of software for data acquisition, data processing and spectral simulation. The initial applications of this new pulsed EPR spectrometer system will be to the catalytic processes of molybdenum enzymes and ferriheme electron-transfer proteins. However, this advanced pulsed EPR instrument will be a powerful tool that will enable the surroundings of paramagnetic metal centers in biological systems to be mapped out in unprecedented detail by biochemists, biophysicists and bioinorganic chemists. A large number of national and international collaborative studies are envisioned once the instrument becomes fully operational, and the software developed in this project will be made generally available to the scientific community.