CAREER: Correlating Metalloenzyme Structure with Reactivity By Tunneling Electrons in Crystals

Cornell University, Ithaca NY

Investigators

Abstract

Ultimately, the essence of life is the controlled movement of charge. The vast number of conformational and chemical states available to the polypeptide chain allows nature to tune the reactivity of metal centers and direct electron flow within and between proteins. The goal of Dr. Crane's research is to develop and apply new photochemical methods for studying the structural basis of redox chemistry and long-range electron transfer (ET) in biology. Photosensitizers will be used to initiate long-range ET in single protein crystals, where structure can be precisely defined by X-ray crystallography. Designed crystal systems that fix donor and acceptor orientations allow effects of intervening protein and water structure on electron tunneling to be probed by mutagenesis and isotopic substitution. ET rates will be determined directly in crystals of metal-modified azurins and crystals of complexes between cytochrome c and cytochrome c peroxidase. Redox reactions at protein metal centers will be driven in crystals by photoinduced ET so that structures of activated states important for catalysis can be determined by cryo-crystallography or time-resolved diffraction techniques. Structures will be determined for peroxidase peroxo-iron and oxo-iron species, important intermediates in biological oxygen activation, and for tryptophan and tyrosine radicals, emerging players in a wide variety of high-potential, biological redox chemistries. Atomic structure will be correlated with electronic structure probed with magnetic and optical spectroscopies to understand the reciprocal tuning of reactivity between metallocofactors and the polypeptide chain. The results of this research will provide sets of long-range ET rates for structural states defined in detail, new structures of hitherto unobserved metalloprotein catalytic species, and new techniques for studying protein dynamics by X-ray diffraction. Educational activities connected with this research aim to relate fundamental concepts in structure, kinetics, thermodynamics and chemical reactivity to complex biological processes such as energy transduction, signal transduction, environmental sensitivity and response. Effort falls into two general categories: 1) mentoring high-school, undergraduate, and graduate students in research; and 2) the development and teaching of new undergraduate and graduate courses at Cornell University. Discovery-based learning at the K-12 level will also be promoted. The research described above is designed to provide projects appropriate for students of all levels. A new graduate course, " the physical chemistry of proteins" is now being taught and a second "Bio-inorganic chemistry" will be presented in 2003. Other course activities include development of an introductory course for freshman chemistry majors in chemical structure and bonding, and an interdepartmental short course in enzyme kinetics. A playful approach to addressing problems will be emphasized in all activities.