A.B. (1971): Brown University
Ph.D. (1976) : Massachusetts Institute of Technology
Postdoctoral Fellowship (1977-1978) : University of California, San Diego
Positions 1967 – 1971 A.B. in Chemistry; Brown University, Rhode Island 1971 – 1972 Schering Corporation; Bloomfield, New Jersey 1972 – 1976 Ph.D. in Organic Chemistry; Massachusetts Institute of Technology 1976 – 1979 Postdoctoral Fellow; University of California at San Diego 1979 – 1986 Assistant Professor of Chemistry; Washington University 1986 – 1990 Assistant Professor of Chemistry; Georgia State University 1992 – 1993 Associate Dean for Mathematics and the Natural Sciences; Georgia State University 1990 – 2002 Associate Professor of Chemistry; Georgia State University 2002 – Professor of Chemistry; Georgia State University 2005 – 2008 Associate Chair of Chemistry, Georgia State University 2008 – 2011 Coordinator for STEM Education Initiatives, Arts and Sciences, GSU 2011 – Director of STEM Education Initiatives, Georgia State University
Iron is required for infection in essentially all bacterial pathogens. In vertebrate infections, the most abundant source of iron is heme, which comes primarily from hemoglobin. Bacteria have developed sophisticated approaches to transport heme into the cytoplasm. We study the heme uptake pathways in two pathogenic organisms.
Streptococcus pyogenes. Heme uptake in Streptococcus pyogenes involves Shr, Shp, SiaA, and an ABC transporter. SiaA has been shown to have axial histidine and methionine ligands. Studies of mutants of these axial ligands, as well as other nearby residues, give insight into the factors that control heme uptake and release. Shr has two heme-binding NEAT domains which have been expressed and purified. Optical and resonance Raman studies, as well as molecular modeling, have been used to assign the axial ligands.
Corynebacterium diphtheriae. The heme uptake pathway of C. diphtheriae also utilizes multiple proteins to bind and transfer heme to be brought into the cell. The heme-binding protein HmuT delivers heme to the HmuUV ABC transporter. Wild-type HmuT and a series of conserved heme pocket residue mutants have been characterized by UV-visible, resonance Raman, and magnetic circular dichroism spectroscopies to determine the axial ligation of this protein. The addition of guanidine hydrochloride results in protein denaturation that shows more than one process. Unfolding is quite slow, perhaps indicating a role for protein-protein docking in heme transfer. The results as a whole indicate that axial ligation, heme pocket hydrogen-bonding interactions, and heme iron oxidation state all play a role in the mechanism of heme uptake and/or release. HtaB and ChtB appear to be interchangeable in the uptake pathway. Current studies focus on ChtB and a protein, ChtA, which appears to be necessary to take up heme from the hemoglobin/haptoglobin complex.
Dr. Dixon is the Director of the Georgia State University Center for STEM Education Initiatives, which seeks to improve science, technology, engineering, and mathematics (STEM) learning at the University. We use innovations in teaching approaches, implementation of evidence-based teaching practices, and significant support for our students to help them graduate with the depth of technical knowledge, the curiosity, and the problem-solving skills to compete in the 21st century. We engage in research to generate new knowledge about teaching, apply theories to the everyday practice of instruction, and develop, evaluate, and critique educational policy.
Current efforts involve curricular reform, establishment of a STEM Tutoring Center, support of Course-based Research Experiences (CUREs) on campus, and working to increase the role of peer-mentoring in student success. The STEM website is found at http://cas.gsu.edu/stem/
- Y. Cao, A. F. Gill, and D. W. Dixon. Synthesis and characterization of a water-soluble porphyrin with a cyclic sulfone. Tetrahedron Lett. 50 (30):4358-4360, 2009.
- R. A. I. Abou-Elkhair, D. W. Dixon, and T. L. Netzel. Synthesis and electrochemical evaluation of conjugates between 2′-deoxyadenosine and modified anthraquinone: Probes for hole transfer studies in DNA. J.Org.Chem. 74 (13):4712-4719, 2009.
- Y. Cao, D. J. Rabinowitz, D. W. Dixon, and T. L. Netzel. Synthesis, electrochemistry and hydrolysis and anthraquinone derivatives. Synth.Commun., 39, 4230-4238, 2009.
- M. Ouattara, E. B. Cunha, X. Li, Y.-S. Huang, D. W. Dixon, and Z. Eichenbaum. Shr of Group A Streptococcus is a new type of composite NEAT protein involved in sequestering heme from methemoglobin. Mol.Microbiol. 78 (3):739-756, 2010.
- R. E. McKnight, E. Reisenauer, M. V. Pintado, S. R. Polasani, and D. W. Dixon. Substituent effect on the preferred DNA binding mode and affinity of a homologous series of naphthalene diimides. Bioorg.Med.Chem.Lett. 21 (14):4288-4291, 2011.