William R Montfort
Professor, Applied Mathematics - GIDP
Professor, BIO5 Institute
Professor, Cancer Biology - GIDP
Professor, Genetics - GIDP
Professor, Molecular and Cellular Biology
Professor, Chemistry and Biochemistry-Sci
Primary Department
(520) 621-1884
Work Summary
We investigate how proteins work in healthy organisms and how they fail in disease. We determine the atomic structures of proteins and the underlying biochemistry that gives rise to protein function. We also develop new proteins as drug targets for treating cancer and cardiovascular disease.
Research Interest
William Montfort, PhD, determines the atomic structures of proteins and seeks to understand how protein structure gives rise to protein function – both in vitro and in living cells. At their heart, the problems have a fundamental structure-function question, but also address questions of importance to human health. Approaches include X-ray crystallography, rapid kinetic measurements, spectroscopy, theory, protein expression, drug discovery, molecular genetics and related techniques.Dr. Montfort is particularly interested in nitric oxide signaling mechanisms. Nitric oxide (NO) is a small reactive molecule produced by all higher organisms for the regulation of an immensely varied physiology, including blood pressure regulation, memory formation, tissue development and programmed cell death. He is interested in two NO signaling mechanisms: binding of NO to heme and the nitrosylation (nitrosation) of cysteines. NO, produced by NO synthase, binds to soluble guanylate cyclase (sGC) at a ferrous heme center, either in the same cell or in nearby cells. Binding leads to conformational changes in heme and protein, and to induction of the protein’s catalytic function and the production cGMP. NO can also react with cysteine residues in proteins, giving rise to S-nitroso (SNO) groups that can alter protein function. He continues to study the mechanistic details surrounding cGMP and SNO production, and the signaling consequences of their formation.For reversible Fe-NO chemistry, Dr. Montfort is studying soluble guanylate cyclase and the nitrophorins, a family of NO transport proteins from blood-sucking insects. Our crystal structures of nitrophorin 4 extend to resolutions beyond 0.9 angstroms, allowing us to view hydrogens, multiple residue conformations and subtle changes in heme deformation. For reversible SNO chemistry, he is studying thioredoxin, glutathione S-nitroso reductase (GSNOR) and also sGC. For regulation in the cell, Dr. Montfort and his group have constructed a model cell system based on a human fibrosarcoma called HT-1080, where sGC, NO synthase, thioredoxin and GSNOR can be manipulated in a functional cellular environment. With these tools, they are exploring the molecular details of NO signaling and whole-cell physiology, and undertaking a program of drug discovery for NO-dependent diseases. Keywords: Structural Biology, Drug Discovery, Cancer, Cardiovascular Disease


Molnar, I., Xu, Y., Zhou, T., Zhou, Z., Su, S., Roberts, S. A., Montfort, W. R., Zeng, J., Chen, M., Zhang, W., Lin, M., Zhan, J., & Molnar, I. -. (2013). Rational reprogramming of fungal polyketide first-ring cyclization. Proceedings of the National Academy of Sciences of the United States of America, 110(14).
BIO5 Collaborators
Istvan Molnar, William R Montfort

Resorcylic acid lactones and dihydroxyphenylacetic acid lactones represent important pharmacophores with heat shock response and immune system modulatory activities. The biosynthesis of these fungal polyketides involves a pair of collaborating iterative polyketide synthases (iPKSs): a highly reducing iPKS with product that is further elaborated by a nonreducing iPKS (nrPKS) to yield a 1,3-benzenediol moiety bridged by a macrolactone. Biosynthesis of unreduced polyketides requires the sequestration and programmed cyclization of highly reactive poly-β-ketoacyl intermediates to channel these uncommitted, pluripotent substrates to defined subsets of the polyketide structural space. Catalyzed by product template (PT) domains of the fungal nrPKSs and discrete aromatase/cyclase enzymes in bacteria, regiospecific first-ring aldol cyclizations result in characteristically different polyketide folding modes. However, a few fungal polyketides, including the dihydroxyphenylacetic acid lactone dehydrocurvularin, derive from a folding event that is analogous to the bacterial folding mode. The structural basis of such a drastic difference in the way a PT domain acts has not been investigated until now. We report here that the fungal vs. bacterial folding mode difference is portable on creating hybrid enzymes, and we structurally characterize the resulting unnatural products. Using structure-guided active site engineering, we unravel structural contributions to regiospecific aldol condensations and show that reshaping the cyclization chamber of a PT domain by only three selected point mutations is sufficient to reprogram the dehydrocurvularin nrPKS to produce polyketides with a fungal fold. Such rational control of first-ring cyclizations will facilitate efforts to the engineered biosynthesis of novel chemical diversity from natural unreduced polyketides.

Fritz, B. G., Roberts, S. A., Ahmed, A., Breci, L., Li, W., Weichsel, A., Brailey, J. L., Wysocki, V. H., Tama, F., & Montfort, W. R. (2013). Molecular model of a soluble guanylyl cyclase fragment determined by small-angle X-ray scattering and chemical cross-linking. Biochemistry, 52(9), 1568-82.

Soluble guanylyl/guanylate cyclase (sGC) converts GTP to cGMP after binding nitric oxide, leading to smooth muscle relaxation and vasodilation. Impaired sGC activity is common in cardiovascular disease, and sGC stimulatory compounds are vigorously sought. sGC is a 150 kDa heterodimeric protein with two H-NOX domains (one with heme, one without), two PAS domains, a coiled-coil domain, and two cyclase domains. Binding of NO to the sGC heme leads to proximal histidine release and stimulation of catalytic activity. To begin to understand how binding leads to activation, we examined truncated sGC proteins from Manduca sexta (tobacco hornworm) that bind NO, CO, and stimulatory compound YC-1 but lack the cyclase domains. We determined the overall shape of truncated M. sexta sGC using analytical ultracentrifugation and small-angle X-ray scattering (SAXS), revealing an elongated molecule with dimensions of 115 Å × 90 Å × 75 Å. Binding of NO, CO, or YC-1 had little effect on shape. Using chemical cross-linking and tandem mass spectrometry, we identified 20 intermolecular contacts, allowing us to fit homology models of the individual domains into the SAXS-derived molecular envelope. The resulting model displays a central parallel coiled-coil platform upon which the H-NOX and PAS domains are assembled. The β1 H-NOX and α1 PAS domains are in contact and form the core signaling complex, while the α1 H-NOX domain can be removed without a significant effect on ligand binding or overall shape. Removal of 21 residues from the C-terminus yields a protein with dramatically increased proximal histidine release rates upon NO binding.

Montfort, W. R., Wales, J. A., & Weichsel, A. (2017). Structure and Activation of Soluble Guanylyl Cyclase, the Nitric Oxide Sensor. Antioxidants & redox signaling, 26(3), 107-121.

Soluble guanylyl/guanylate cyclase (sGC) is the primary receptor for nitric oxide (NO) and is central to the physiology of blood pressure regulation, wound healing, memory formation, and other key physiological activities. sGC is increasingly implicated in disease and is targeted by novel therapeutic compounds. The protein displays a rich evolutionary history and a fascinating signal transduction mechanism, with NO binding to an N-terminal heme-containing domain, which activates the C-terminal cyclase domains. Recent Advances: Crystal structures of individual sGC domains or their bacterial homologues coupled with small-angle x-ray scattering, electron microscopy, chemical cross-linking, and Förster resonance energy transfer measurements are yielding insight into the overall structure for sGC, which is elongated and likely quite dynamic. Transient kinetic measurements reveal a role for individual domains in lowering NO affinity for heme. New sGC stimulatory drugs are now in the clinic and appear to function through binding near or directly to the sGC heme domain, relieving inhibitory contacts with other domains. New sGC-activating drugs show promise for recovering oxidized sGC in diseases with high inflammation by replacing lost heme.

Gloss, A. D., Vassão, D. G., Hailey, A. L., Nelson Dittrich, A. C., Schramm, K., Reichelt, M., Rast, T. J., Weichsel, A., Cravens, M. G., Gershenzon, J., Montfort, W. R., & Whiteman, N. K. (2014). Evolution in an ancient detoxification pathway is coupled with a transition to herbivory in the drosophilidae. Molecular biology and evolution, 31(9), 2441-56.

Chemically defended plant tissues present formidable barriers to herbivores. Although mechanisms to resist plant defenses have been identified in ancient herbivorous lineages, adaptations to overcome plant defenses during transitions to herbivory remain relatively unexplored. The fly genus Scaptomyza is nested within the genus Drosophila and includes species that feed on the living tissue of mustard plants (Brassicaceae), yet this lineage is derived from microbe-feeding ancestors. We found that mustard-feeding Scaptomyza species and microbe-feeding Drosophila melanogaster detoxify mustard oils, the primary chemical defenses in the Brassicaceae, using the widely conserved mercapturic acid pathway. This detoxification strategy differs from other specialist herbivores of mustard plants, which possess derived mechanisms to obviate mustard oil formation. To investigate whether mustard feeding is coupled with evolution in the mercapturic acid pathway, we profiled functional and molecular evolutionary changes in the enzyme glutathione S-transferase D1 (GSTD1), which catalyzes the first step of the mercapturic acid pathway and is induced by mustard defense products in Scaptomyza. GSTD1 acquired elevated activity against mustard oils in one mustard-feeding Scaptomyza species in which GstD1 was duplicated. Structural analysis and mutagenesis revealed that substitutions at conserved residues within and near the substrate-binding cleft account for most of this increase in activity against mustard oils. Functional evolution of GSTD1 was coupled with signatures of episodic positive selection in GstD1 after the evolution of herbivory. Overall, we found that preexisting functions of generalized detoxification systems, and their refinement by natural selection, could play a central role in the evolution of herbivory.

Purohit, R., Fritz, B. G., The, J., Issaian, A., Weichsel, A., David, C. L., Campbell, E., Hausrath, A. C., Rassouli-Taylor, L., Garcin, E. D., Gage, M. J., & Montfort, W. R. (2014). YC-1 binding to the β subunit of soluble guanylyl cyclase overcomes allosteric inhibition by the α subunit. Biochemistry, 53(1), 101-114.

PMID: 24328155;Abstract:

Soluble guanylate cyclase (sGC) is a heterodimeric heme protein and the primary nitric oxide receptor. NO binding stimulates cyclase activity, leading to regulation of cardiovascular physiology and making sGC an attractive target for drug discovery. YC-1 and related compounds stimulate sGC both independently and synergistically with NO and CO binding; however, where the compounds bind and how they work remain unknown. Using linked equilibrium binding measurements, surface plasmon resonance, and domain truncations in Manduca sexta and bovine sGC, we demonstrate that YC-1 binds near or directly to the heme-containing domain of the β subunit. In the absence of CO, YC-1 binds with a K d of 9-21 μM, depending on the construct. In the presence of CO, these values decrease to 0.6-1.1 μM. Pfizer compound 25 bound ∼10-fold weaker than YC-1 in the absence of CO, whereas compound BAY 41-2272 bound particularly tightly in the presence of CO (Kd = 30-90 nM). Additionally, we found that CO binds much more weakly to heterodimeric sGC proteins (Kd = 50-100 μM) than to the isolated heme domain (K d = 0.2 μM for Manduca β H-NOX/PAS). YC-1 greatly enhanced binding of CO to heterodimeric sGC, as expected (Kd ∼ 1 μM). These data indicate the α subunit induces a heme pocket conformation with a lower affinity for CO and NO. YC-1 family compounds bind near the heme domain, overcoming the α subunit effect and inducing a heme pocket conformation with high affinity. We propose this high-affinity conformation is required for the full-length protein to achieve high catalytic activity. © 2013 American Chemical Society.