CAREER: Understanding the Role of Amino Acid Radicals in Electron Transfer

University Of Montana, Missoula MT

Investigators

Abstract

Amino acid radicals are vital to the catalytic mechanisms of many fundamental biological processes, including nucleic acid metabolism, DNA repair, photosynthesis, and aerobic respiration. Amino acid radicals may serve as "sinks" for positive charges during oxidation, to facilitate very long-range (>25 angstrom) electron transfer in proteins via multi-step tunneling. Yet despite the significance of amino acid radicals in biology, their electrochemical and electron transfer properties are not well defined. In this project, these properties will be measured directly using the beta-sheet protein azurin and the 4-helix bundle protein cytochrome c' as model systems. To investigate the effects of electrochemical potentials on electron transfer mechanisms, non-natural Trp and Tyr amino acids will be incorporated at specific sites of the polypeptide chains. This extends the range of electrochemical potentials ~ +/- 0.4 V compared with the natural amino acids. Moreover, several Tyr analogs have pKa values within the biological pH range. These offer a unique opportunity to kinetically separate electron transfer from the accompanying proton transfer step that is obligatory in biological electron transfer. The analogs also provide distinctive spectroscopic handles for defining local amino acid environments. Broader impacts: Coupled with the proposed research is the development of a research-oriented upper level biochemistry course that integrates lectures into laboratory time. The goals of the course are to expose more undergraduates to scientific research and encourage them to pursue careers in science. Guidelines for course evaluation and outcomes assessment are also included. The course also provides a graduate student or postdoctoral scholar with the resources needed to explore innovative ways of teaching and presenting course material. Special efforts are made to recruit native American undergraduate and graduate students to work on the project. This is greatly facilitated by existing contacts with tribal colleges in Montana.