Professor Marshall's research interests include structure-based drug design; protein engineering; peptidomimetics; G-protein couped receptors; ErbB-tyrosine kinase receptors; virtual screening; combinatorial chemistry; solid-phase organic chemistry.
My interests spring from an eclectic background teaching physiology and pharmacology while developing computer-aided molecular graphics and drug design methodology. Not surprisingly, computational chemistry and its focus on molecular recognition became a dominant focus. In the past, enzyme inhibitors (HIV-protease) and peptide hormones involved in blood pressure regulation (angiotensin and bradykinin) dominated my lab. Now, experimentally determining precise intermolecular distances in biomolecular complexes has become a focus using modern pulse EPR spectrometers.
Specific Research Projects
Inhibitors of dimerization of ErbB tyrosine-kinase transmembrane receptors. These receptors are overexpressed in many cancers and are a useful therapeutic target in oncology. (see Yang et al. Chem Biol Drug Design, 76:1, 2010) catalysts. (Collaboration with Profs. Linda J. Pike and Craig Lockhart, WUSM)
Steric discrimination between acetylcholine, the substrate, and organophosphates that inhibit acetylcholinesterase (AChE) and serve as neurotoxins. (Collaboration with Prof. Terrone Rosenberry, Mayo Clinic)
Allosteric activators of the enzyme ACE2 for treatment of cardiovascular disease. (Collaboration with Dr. Salva Epstein, Division of Cardiology, WUSM)
Inhibitors of two-component systems that regulate virulence in pathogenic bacteria. Two-component signal transduction (TCST) is the predominant signaling scheme used in bacteria to sense and respond to environmental changes in order to survive and thrive. A typical TCST system consists of a sensor histidine kinase to detect external signals, and an effector response regulator to respond to external changes. In the signaling scheme, the histidine kinase phosphorylates and activates the response regulator, which functions as a transcription factor to modulate gene expression. One promising strategy towards antibacterial development is to target TCST regulatory systems, specifically the response regulators to disrupt the expression of genes important for virulence. In Salmonella enterica, for example, the PhoQ/PhoP signal transduction system is used to sense and respond to low magnesium levels, and regulates the expression for over 40 genes necessary for growth under these conditions, and more interestingly, genes that are important for virulence. (Collaboration with Profs. Eduardo Groisman, Jeff Henderson and Jim Havrenek of WUSM and Prof. Ann Stock of Rutgers)
Our interest in protein engineering focuses on enhanced stability of designed protein secondary-structure scaffolds to force the particular sequence chosen to fold into the desired three-dimensional target. Initially, we have been involved in design and experimental validation of semi-rigid secondary structure mimetics.
A. Helical peptidomimetics - Protein helices are often used as recognition motifs in protein/protein and protein/nucleic acid control systems. As such, drug-like mimetics has potential therapeutic utility. We have designed and synthesized substituted phenyldipyridyl helix mimetics for this purpose (Bourne, G.T., Kuster, D.J., and Marshall, G.R. 2010. Bipyridal-Based -Helical Mimetics. Chemistry Eur J published online).
B. Beta-Hairpin scaffolds - Evaluation of a “designed” beta-hairpin FSD-1 as a potential scaffold led us to conclude that its stability was limited at best (Feng, J.A., Kao, J., and Marshall, G.R. 2009. A second look at mini-protein stability: analysis of FSD-1 using circular dichroism, differential scanning calorimetry, and MD simulations. Biophys J 97(10): 2803-2810).
Modeling molecular requires validation of any significant conclusions by experimental techniques. In particular, both accurate and precise distance measurements have to be made at the subnanometer scale. For this reason, spectroscopic techniques such as NMR and EPR are necessary auxiliaries to molecular modeling and molecular dynamics simulations. We have utilized these techniques in studies of the rhodopsin/transducin system of signal transduction. Rhodopsin is the prototypical G-protein coupled receptor and transducin is its G-protein partner in vision.The structure of the C-terminal recognition motif of the alpha subunit of transducin was determined by transfer NMR (Kisselev, O.G., Kao, J., Ponder, J.W., Fann, Y.C., Gautam, N., and Marshall, G.R. 1998. Light-activated rhodopsin induces structural binding motif in G protein alpha subunit. Proc Natl Acad Sci USA 95(8): 4270-4275). More recently, DEER EPR spectroscopy was used to estimate the entropy of peptide binding to photoactivated rhodopsin (Van Eps, N., Anderson, L.L., Kisselev, O.G., Baranski, T.J., Hubbell, W.L., and Marshall, G.R. 2010. EPR Studies of Functionally Active, Nitroxide Spin-Labeled Analogs of the C-Terminus of a G-Protein Alpha Subunit. Biochemistry 49, 6877-6886). Modern pulse EPR spectroscopy allows measurement of interspin distance distributions up to 8 nM. The precision of the measurement depends on the rigidity of the spin label with respect to the secondary structure examined. Nitroxide labels normally used in biological systems are two flexible to determine precise interspin distances. Novel amide-nitroxide spin labels have been developed to be incorporated into peptide backbones of proteins biosynthetically. (Collaboration with Prof. Gail Fanucci, University of Florida, and Prof. Hiro Suga, University of Tokyo)
Awards and Honors
1987 –Medal XL-Lecia Politechniki Lodzkiej (40th Anniversary of Polytechnika, Lodz, Poland)
1988 –Medicinal Chemistry Award, Medicinal Chemistry Division, American Chemical Society
1993 –Doctora Honoris Causa, Politechniki Lodzkiej, Oct. 1, 1993 (Polytechnika, Lodz, Poland)
1994 –Vincent duVigneaud Award, Gordon Conference on Peptides, Ventura, CA, Feb. 17, 1994
1996 –Midwest Award, St. Louis Regional Division, American Chemical Society
1996 –Science and Technology Award, St. Louis Regional Commerce and Growth Association
1996 –George B. Koelle Award, Mid-Atlantic Pharmacology Society
1997 –Medal 50-Lecia Politechniki Lodzkiej (50th Anniversary of Polytechnika, Lodz, Poland)
2000 –Cathay Award, Chinese Peptide Society, Mt. Huangshan, China
2000 – Taito M. Soine Memorial Award, Department of Medicinal Chemistry, University of Minnesota
2001 – Merrifield Award, American Peptide Society, San Diego, CA
2003 – Excellence in Life Sciences Award for Serial Entrepreneurship, Missouri Biotechnology Association
2005 – Inaugural Lee Wing Nam Professor, School of Biological Sciences, Nanyang Technological University, Singapore
2006 – 16th Smissman Memorial Lecturer, Department of Medicinal Chemistry, University of Kansas
2007 – Burger Lecturer, Department of Chemistry, University of Virginia
2008 – Inaugural Member, Medicinal Chemistry Hall of Fame, American Chemical Society
2009 – Plenary Lecturer – Centenary Celebration of Medicinal Chemistry, 238th ACS National Symposium, Washington, D.C.
2011 (fall semester) – Visiting Professor, Universitá di Roma La Sapienza