Faculty Profile

Faculty Profile of F. Ann Walker

F. Ann Walker

Regents Professor

Email: awalker@email.arizona.edu
Building: OC 204A
Phone: 520-621-8645

Honors


  • Galileo Circle Fellow, College of Science, University of Arizona, 2009
  • Alfred Bader Award in Bioinorganic Chemistry, American Chemical Society, 2006
  • Alexander von Humboldt Senior Research Award, 2003-2004
  • Luigi Sacconi Medal, Inorganic Chemistry Division, Italian Chemical Society, 2001
  • Inducted as Regents Professor, University of Arizona, 2001
  • Francis P. Garvin - John M. Olin Medal of the American Chemical Society, 2000

Education and Appointments


  • B.A. 1962, The College of Wooster
  • Ph.D. 1966, Brown University
  • Postdoc 1966-67, UCLA

Research Interests


  • Biochemistry
  • Inorganic
  • Physical
  • Bioinorganic
  • Biophysics
  • Chemical Biology
  • Chemical Reaction Dynamics/Kinetics/Interactions
  • Protein and Membrane Biochemistry
  • Spectroscopy/molecular Structure
  • Structural Biology

Research Summary

Bioinorganic Chemistry of Hemes and Heme Proteins; Site-Directed Mutagenesis, Electrochemistry, NMR and EPR Spectroscopies.

We study a wide range of bioinorganic and biological systems, all of which fall under the general theme of gaining a better understanding of the heme centers in heme proteins that are vital to the life of almost all living organisms. The overall goals of this research are:

  1. To characterize the nitrosylheme proteins from blood-sucking insects. Nitric oxide has been shown to be an important neurotransmitter, vasodilator, and other chemical messenger. We have recently shown that Rhodnius prolixus (the "kissing bug")1,2 and Cimex lectularius (the bedbug)3 each have at least one NO-carrying heme protein in their saliva that helps them succeed in their goal of living on the blood of higher animals. In collaboration with the research group of Dr. William Montfort, Dept. of Chemistry and Biochemistry, and others off-campus, we are investigating the 3-D structures, spectroscopy (NMR, EPR, UV-vis, MCD, Mössbauer and resonance Raman), thermodynamics (kinetics and equilibria of NO binding, and reduction potentials in the absence and presence of NO) of the NO-binding heme proteins from both of these insects4. Current research on these proteins includes preparation and investigation of appropriate site-directed mutants to test hypotheses as to which amino acid side chains affect NO and histamine binding and release.
  2. To prepare and investigate site-directed mutants of the membrane-bound cytochrome b of the bc1 complex (respiratory Complex III) of the photosynthetic bacterium Rhodobacter sphaeroides. The mutants are chosen so as to interfere with the binding of one of the histidine ligands of either the high- or the low-potential heme of cytochrome b, in order to determine how this interference affects the EPR spectrum and the reduction potential of that heme, and the rate of electron transfer through the low-potential half of the bifurcated electron transfer pathway of the Q-cycle.
  3. To investigate the reaction mechanisms, substrate specificity and domain interactions of cytochrome P450BM3 and several insect cytochromes P450. Cytochromes P450 are monooxygenase enzymes that comprise about 10% of the protein found in the human liver. They hydroxylate or epoxidize a wide range of substrates including (but not limited to) steroid hormones and xenobiotics. P450BM3, from Bacillus megaterium, has been described as a "complete enzyme" because in one polypeptide it has both the heme and reductase domains necessary to catalyze the oxidation of substrates in the presence of molecular oxygen and NADPH, and its reactions are 100-1000 times faster than those of reconstituted microsomal P450s. We are using the "scanning chimeragenesis" approach to create P450BM3 mutants with altered substrate specificity. Techniques being used include genetic engineering, protein expression and purification, optical, multidimensional NMR, EPR and pulsed EPR spectroscopies, stopped-flow kinetics, gas chromatography and mass spectrometry (for identification of the products of enzymatic reactions).
  1. J. M. C. Ribeiro, J. M. H. Hazzard, R. Nussenzveig, D. Champagne, F. A. Walker, Science 1993, 260, 539.
  2. J. M. C. Ribeiro, F. A. Walker, J. Exper. Med. 1994, 180, 2251.
  3. J. G. Valenzuela, F. A. Walker, J. M. C. Riberiro, J. Exper. Biol. 1995, 198, 1519.
  4. F. A. Walker, J. Inorg Biochem. 2005, 99, 216-236.


Selected Publications

  • "Effect of the N-Terminus on Heme Cavity Structure, Ligand Equilibrium and Rate Constants, and Reduction Potentials of Nitrophorin 2 from Rhodnius prolixus," Berry, R. E.; Shokhireva, T. Kh.; Filippov, I.; Shokhirev, M. N.; Zhang, H.; Walker, F. A. Biochemistry 2007, 46, 6830-6843. (DOI: 10.1021/bi7002263)

  • "Assignment of Ferriheme Resonances for High- and Low-Spin Forms of the Symmetrical Hemin-Reconstituted Nitrophorins 1-4 by 1H and 13C NMR Spectroscopy: The Dynamics of Heme Ruffling Deformations," Shokhireva, T. Kh.; Shokhirev, N. V.; Berry, R. E.; Zhang, H.; Walker, F. A. J. Biol. Inorg. Chem. 2008, 13, 941-959. (DOI: 10.1007/s00775-008-0381-8)

  • Effect of Mutation of Carboxylate Side-Chain Amino Acids Near the Heme on the Midpoint Potentials and Ligand Binding Constants of Nitrophorin 2 and its NO, Histamine and Imidazole Complexes," Berry, R. E.; Shokhirev, M. N.; Ho, A. Y. W.; Yang, F.; Shokhireva, T. K.; Zhang, H.; Weichsel, A.; Montfort, W. R.; Walker, F. A. J. Am. Chem. Soc. 2009, 131, 2313-2327. (DOI: 10.1021/ja00006a066)

  • "1H and 13C NMR Spectroscopic Studies of the Ferriheme Resonances of the Low- Spin Imidazole, Histamine and Cyanide Complexes of wt Nitrophorin 2 and NP2(V24E) as a Function of pH," Yang, F.; Knipp, M.; Berry, R. E.; Shokhireva, T. K.; Zhang, H.; Walker, F. A. J. Biol. Inorg. Chem. 2009, 14, 1077-1095. (DOI: 10.1007/200775-009-00551-3))

  • "Scanning Chimeragenesis: The Approach Used to Change the Substrate Selectivity of Fatty Acid Monooxygenase CYP102A1 to That of Terpene ω-Hydroxylase CYP4C7," Chen, C.-K. J.; Berry, R. E.; Shokhireva, T. K.; Murataliev, M. B.; Zhang, H.; Walker, F. A. J. Biol. Inorg. Chem. 2010, 15, 159-174. (DOI: 10.1007/s00775-009-0580-y))

  • "The Unprecedented Peroxidase-like Activity of Rhodnius prolixus Nitrophorin 2: Identification of the [FeIV=O Por⋅]+ and [FeIV=O Por](Tyr38⋅) Intermediates and Their Role(s) in Substrate Oxidation," Singh, R.; Berry, R. E.; Yang, F.; Zhang, H.; Walker, F. A.; Ivancich, A. I. Biochemistry 2010, 49, 8857-8872. (DOI: 10.1021/bi100499a))


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