BMCB-Faculty Research, Michael A. Cusanovich

Regents Professor of Biochemistry & Molecular Biophysics and Chemistry
Ph.D., University of California, San Diego

Protein structure and function, biological electron transfer, sensor proteins, bacterial evolution.

Research Interests

The Cusanovich laboratory focuses on two critically important issues. First, we study biological recognition, that is, the chemical and structural interactions that mediate protein-protein interactions and which control biological specificity. Metabolic processes occur in a complex milieu, yet with high fidelity, with specificity derived in large measure by the formation of transient and long-lived metabolically relevant complexes. Second, we study functionally relevant protein motions (protein dynamics). Proteins are not static structures and in some cases undergo a variety of relatively rapid large motions (protein dynamics). These motions are functionally relevant in some cases and provide mechanisms to facilitate biological processes. Our approach to these problems uses a variety of kinetic and structural approaches to relate the time course of events to structural and chemical features of these macromolecules. These techniques include electrochemistry, spectroscopy, calorimetry, NMR, x-ray crystallography, stopped-flow, laser flash photolysis and perturbation methods as well as site-directed mutagenesis and computer modeling of the kinetic mechanism and protein structure. Two structurally well defined model systems are utilized.

The bacterial cytochromes c2 which are structural homologs of mitochondrial cytochrome c, are well characterized with substantial structural data available (both NMR solution structures and x-ray structures). The cytochromes c2 have as a natural electron acceptor, photosynthetic reaction centers, thus, we can elucidate the specific chemical and structural interactions that direct the flow of electrons from the cytochrome to the photosynthetic reaction center, and not to other thermodynamically allowable pathways. This system is of particular value as a model system since we can initiate electron transfer with a pulse of laser light, thus kinetic measurements can be made in real time and directly reflect the function of the interacting proteins.

Our second area of focus is on Photoactive Yellow Protein (PYP). This is a signaling protein involved in sensing blue light. However, and more importantly, PYP is the structural prototype for the super family of sensor proteins which contain a PAS domain. The PAS domain containing super family has a common structural motif, which is found throughout the phylogenetic tree. Interestingly, this motif has evolved to sense a wide range of stimuli, ranging from light, oxygen, redox potential, and small molecules to electric field changes. In all cases the stimulus initiates structural changes which result in the conversion to the signaling state. In the signaling state, the PAS domain can directly regulate transcription or activate an enzyme, for example, a kinase, which then elicits a response. Thus PYP serves as an experimental model system for a broad and diverse family of sensor proteins. In the context of our general interest in biological recognition and protein dynamics the conversion of PAS domains from the resting state to the signaling state, is inherently a relatively fast functionally relevant dynamic process. Moreover, the interaction of the signaling state with the appropriate reaction partner (for example, a kinase) requires biological recognition. It is important to note that many of the techniques used by us (e.g., site-directed mutagenesis and laser flash photolysis) are the same for both the cytochrome and the PYP studies.

Select Publications

Any link on the below references will take you off of the BMCB site and to an abstract of that particular paper.

Kyndt, J.A., J.C. Fitch, T.E. Meyer, and M.A. Cusanovich. 2007. The photoactivated PYP domain of Rhodospirillum centenum Ppr accelerates recovery of the bacteriophytochrome domain after white light illumination. Biochemistry 46: 8256-8262.

Hoersch, D., H. Otto, C.P. Joshi, B. Borucki, M.A. Cusanovich, and M.P. Heyn. 2007. Role of a conserved salt bridge between the PAS core and the N-terminal domain in the activation of the photoreceptor photoactive yellow protein. Biophysical Journal 93: 1687-1699.

Devanathan, S., Z. Salamon, G. Tollin, J.C. Fitch, T.E. Meyer, E.A. Berry, and M.A. Cusanovich. 2007. Plasmon waveguide resonance (PWR) spectroscopic evidence for differential binding of oxidized and reduced Rhodobacter capsulatus cytochrome c2 to the cytochrome bc1 complex mediated by the conformation of the Rieske iron-sulfur protein. Biochemistry 46: 7138-7145.

Kyndt, J.A., S.N. Savvides, S. Memmi, M. Koh, J.C. Fitch, T.E. Meyer, J.J. Van Beeumen, and M.A. Cusanovich. 2007. Structural role of Y98 in PYP: effects on fluorescence, gateway and photocycle recovery. Biochemistry 46: 95-105.

Cheng, G., M.A. Cusanovich, and V.H. Wysocki. 2006. Properties of the dark and signaling states of photoactive yellow protein probed by solution phase hydrogen/deuterium exchange and mass spectrometry. Biochemistry 45: 11744-11751.

Borucki, B., C.P. Joshi, H. Otto, M.A. Cusanovich, and M.P. Heyn. 2006. The transient accumulation of the signaling state of photoactive yellow protein is controlled by the external pH. Biophysical Journal 91: 2991-3001.

Joshi, C.P., B. Borucki, H. Otto, T.E. Meyer, M.A. Cusanovich, and M.P. Heyn. 2006. Photocycle and photoreversal of photoactive yellow protein at alkaline pH: Kinetics, intermediates, and equilibria. Biochemistry 45: 7057-7068.

Cheng, G., V.H. Wysocki, and M.A. Cusanovich. 2006. Local stability of Rodobacter capsulatus cytochrome c2 probed by solution phase hydrogen/deuterium exchange and mass spectrometry. Journal of the American Society for Mass Spectrometry 17: 1518-1525.

Van Driessche, G., B. Devreese, J.C. Fitch, T.E. Meyer, M.A. Cusanovich, and J.J. Van Beeumen. 2006. GHP, a new c-type green heme protein from Halochromatium salexigens and other proteobacteria. The FEBS Journal 273: 2801-2811.

Contact Information

Mailing:
Michael A. Cusanovich, Regents Professor
Department of Biochemistry & Molecular Biophysics
University of Arizona
Biological Sciences West 430
P.O. Box 210088
Tucson, AZ 85721-0088

Web Site: Home Page

Telephone:
520-621-7533 (Office)
520-621-5256 (Lab)

Fax:
520-626-9204

Email:
cusanovi@email.arizona.edu

Please e-mail any comments to:
bmcb@email.arizona.edu