Eric A. Toth
Biochemistry and Molecular Biology
9600 Gudelsky Drive
I received a B.A. in Biochemistry from the University of Pennsylvania and a Ph.D. in Biochemistry from the University of California, Los Angeles (UCLA). I then conducted postdoctoral training at UCLA in the Department of Chemistry and Biochemistry and Harvard Medical School in the Department of Biological Chemistry and Molecular Pharmacology prior to joining the faculty at the University of Maryland in the Department of Biochemistry and Molecular Biology in 2004. In 2011, I became a Section Leader in Structural Biology in the Center for Biomolecular Therapeutics. I am a member of the Molecular and Structural Biology Program within the University of Maryland Marlene and Stewart Greenebaum Cancer Center Program in Oncology and co-Director of the Structural Biology Shared Service. As such, I collaborate with both basic and clinical research investigators to study the basic mechanisms of cancer development and metastasis and to identify candidate proteins that may serve as targets for therapeutic intervention.
As a Section Leader in Structural Biology at the Center for Biomolecular Therapeutics, I am responsible for using X-ray crystallographic techniques to accelerate the development of agenst that modulate the function of a wide array of potential therapeutic targets. These targets have been selected through consultations with investigators in the University System of Maryland and beyond. A significant fraction of the Structural Biology portfolio arose via my association with the University of Maryland Marlene and Stewart Greenebaum Cancer Center and thus entails an effort to develop both research tools that will help us understand the root causes of various cancers and therapeutics that will combat those diseases. In this capacity, I am engaged in both smaller scale collaborations aimed at augmenting the research programs of other investigators and a research program that I direct. In the context of these two types of initiatives, my research has three main foci: (1) Structure-based drug design; (2) Oxidative DNA damage repair; and (3) Neurological diseases involving the kynurenine pathway of tryptophan degradation.
Structure-based drug design:
In order to develop small-molecule agents that specifically modulate the activity of a given therapeutic target macromolecule, it is often the case that an initial “lead compound” will require significant modifications to achieve the required efficacy. X-ray crystallography can play a pivotal role in determining which changes to a given lead compound are likely to improve interactions with a given target. This stems from the fact that X-ray crystallography provides an atomic level picture of the molecule under study. Therefore, we can visualize in great detail where on a given target macromolecule the lead compound of interest interacts, which functional groups on the lead compound make critical interactions, and which functional groups do not productively participate in binding. This information allows us to make rational choices regarding which additions or subtractions to the lead compound should be given the highest priority. This information is used, in conjunction with data from the Computer-Aided Drug Design (CADD) and Medicinal Chemistry groups at the Center for Biomolecular Therapeutics, to develop a plan for creating the next generation of inhibitors. It is via this pipeline that we take the initial agents that produce the desired effects against a given target and eventually transition them to the clinic. One example of an ongoing effort in this area is the development of inhibitors that block the S100B-p53 interaction. Blocking this interaction can restore the tumor suppressor activity of p53 in certain cancers such as malignant melanoma. This project has been a long-term effort of Dr. David Weber, and my laboratory has collaborated with the Weber lab to obtain high-resolution structural data describing the interactions between small-molecule inhibitors and S100B. An example of one of our structures is shown below:
Oxidative DNA damage repair:
Reactive oxygen species (ROS), both endogenous and exogenous (e.g., ionizing radiation) threaten genomic integrity by inflicting DNA damage, including chemical modification of the nucleobases. One particularly deleterious type of ROS-induced damage is 8-oxo-7,8-
dihydrodeoxyguanine (8-oxo-dG, or Go). In the absence of repair, Go lesions cause G:C to T:A mutations due to the propensity of Go to base-pair with adenine. Decreased oxidative DNA damage repair capacity contributes to both premature aging and cancer. In fact, mutations in hMYH are implicated in a colorectal adenoma and carcinoma predisposition syndrome called MYH-associated polyposis (MAP). Base excision repair (BER) eliminates ROS-induced DNA damage. The first step in long-patch (LP)-BER is performed by a lesion-specific DNA glycosylase such as MutY homologue (MYH), which selectively excises adenines that are mispaired with Go lesions. The resulting apurinic/apyrimidinic (AP) product is transferred to AP-endonuclease 1 (APE1) for further processing and downstream enzymes complete repair (i.e. steps 3-5, below). Regulation of BER activity via protein-protein interactions is a poorly-understood feature of BER. The control of BER via interactions between MYH, APE1 and the Rad9, Rad1, and Hus1 (9-1-1) checkpoint complex is a major focus of our research.
As part of our investigation of regulatory protein interactions that control oxidative DNA damage repair, we determined the first crystal structure of human MYH and identified the interdomain
connector (IDC) as a region important for facilitating interactions with 9-1-1 and APE1. In addition, we used NMR to identify two regions on APE1 that interact with the IDC.
Taken together, our results are consistent with the hypothesis that recruitment of 9-1-1 to sites of DNA damage facilitates a dynamic interplay between BER enzymes by sequestering them at sites of damage. Such interplay could help ensure that toxic BER intermediates do not escape the pathway and imperil the integrity of the genome.
The kynurenine pathway:
A1. Dysregulation of the kynurenine pathway (KP) of tryptophan (Trp) degradation causes brain disorders: The KP accounts for >90 % of Trp metabolism in peripheral organs, shuttling Trp to de novo NAD+ synthesis for use in fundamental metabolic processes. In the brain, the KP produces neuroactive metabolites such as quinolinic acid (QA), 3-hydroxykynurenine (3-HK), and kynurenic acid (KYNA), which play important roles in neurodegenerative phenomena and cognitive processes. Of the three, the potent biological activity of QA along with its implication in a number of neurodegenerative conditions makes it the leading target for pharmacological modulation and thus understanding the biology of QA metabolism is paramount. QA is formed by 3-hydroxyanthranilic acid oxygenase (3HAO, step 3, red box below). Underscoring its importance, QA exerts neurotoxic effects by a number of mechanisms. One mechanism is via the generation of free radicals which destroy neurons. In addition, QA is a selective N-methyl-D-aspartate receptor (NMDAR) agonist that causes excitotoxic lesions when administered intracerebrally. QA can also trigger excessive glutamate release, which leads to neurotoxicity. These and other neurotoxic effects are exacerbated by the lack of an effective removal system which likely contributes to its potent excitotoxic properties in vivo. A beneficial property of QA is that it serves as a precursor for de novo NAD+ biosynthesis. In fact, the only known mechanisms for QA removal are brain efflux and shuttling of QA to NAD+ biosynthesis by quinolinic acid phosphoribosyltransferase (QPRT, step 4 below). Thus, QPRT, which metabolizes QA, acts as the “gatekeeper” of the pathway. In fact, our recent evidence shows that mice with a genetic ablation of QPRT show both increased QA levels and pronounced neurodegeneration in the striatum. Interestingly, lack of QPRT in these mice also significantly increases the levels of the amyloid peptides Ab1-40 and Ab1-42 in the brain. Thus, the main focus of this proposal is to understand how QA levels are regulated and further how to potentially exploit this regulation to treat neurodegenerative disease.
QA is an important metabolite in a metabolic pathway, and as such changes in QA levels can affect the levels of other neuroactive metabolites in the pathway. 3-HK is produced by kynurenine 3-monooxygenase (KMO, step 2 above) and can, like QA, generate free radicals that are neurotoxic. However, baseline levels of 3-HK in the brain are typically very low. KYNA, which is neuroprotective against free radicals produced by QA and 3-HK, also plays a major role in cognition. Enhanced KYNA synthesis causes distinct cognitive impairments in experimental animals. Conversely, inhibition of KYNA synthesis in the brain results in improved spatial learning and memory. Thus, while QA levels are the primary determinant of toxicity, therapeutic strategies will need to consider secondary effects by monitoring the levels of QA, 3-HK, and KYNA.
As part of our efforts to understand the regulation of this pathway, we solved the first crystal structure of human QPRT bound to its inhibitor phthalic acid (below). These studies will set the stage for the development of biological tools that we can use to manipulate the KP in vivo using the well-established rat and mouse models of our collaborator, Dr. Robert Schwarcz of the Maryland Psychiatric Research Institute.
Current Staff Members:
- Swarna Pidugu, postdoctoral fellow
- Carlos Alejandro Velikovsky, postdoctoral fellow
- Revanth Baddam, undergraduate intern
- JC Emmanuel Mbimba, undergraduate intern
- Tin Lok Wong, undergraduate intern
- Cavalier MC, Pierce AD, Wilder PT, Alasady MJ, Hartman KG, Neau DB, Foley TL, Jadhav A, Maloney DJ, Simeonov A, Toth EA, Weber DJ. (2014) Covalent Small Molecule Inhibitors of Ca(2+)-Bound S100B. Biochemistry, 53(42): 6628-40.
- Jin, J., Hwang, B-J., Chang, P-W., Toth, E.A., and Lu, A-L. (2014) Interactions of apurinic/apyrimidinic endonuclease 2 (Apn2) with Myh1 DNA glycosylase in fission yeast DNA Repair. DNA Repair, 15(1): 1-10.
- Malik, S.S., Patterson, D.N., Ncube, Z., and Toth, E.A. (2014) The crystal structure of human quinolinic acid phosphoribosyltransferase in complex with its inhibitor phthalic acid. Proteins: Structure, Function, and Bioinformatics, 82(3): 405-14.
- Manvilla, B.A., Pozharski, E., Toth, E.A., and Drohat, A.C. (2013) Crystal structure of human apurinic/apyrimidinic endonuclease 1 with the essential Mg2+ cofactor. Acta Crystallographica D69, 2555-62.
- Luncsford, P.J., Manvilla, B.A., Patterson, D.N., Malik, S.S., Jin, J., Hwang, B-J., Gunther, R., Kalvakolanu, S., Lipinski, L.J., Yuan, W., Lu, W., Drohat, A.C., Lu, A-L., and Toth, E.A. (2013) Coordination of MYH DNA glycosylase and APE1 endonuclease activities via physical interactions. DNA Repair, 12(12), 1043-52.
- Pazgier M, Ericksen B, Ling M, Toth EA, Shi J, Li X, Galliher-Beckley A, Lan L, Zou G, Zhan C, Yuan W, Pozharski E, Lu W. (2013) Structural and functional analysis of the pro-domain of human cathelicidin, LL-37. Biochemistry, 52(9): 1547-58.
- Erzurumlu, Y., Kose, F.A., Gozen, O., Gozuacik, D., Toth, E.A., Ballar, P. (2013) A unique IBMPFD-related P97/VCP mutation with differential binding pattern and subcellular localization. Int. J. Biochem. & Cell Biol., 45(4): 773-82.
- Kishor A, Tandukar B, Ly YV, Toth EA, Suarez Y, Brewer G, Wilson GM. (2013) Hsp70 is a novel posttranscriptional regulator of gene expression that binds and stabilizes selected mRNAs containing AU-rich elements. Mol. Cell. Biol., 33(1): 71-84.
- McKnight, L. E., Raman, E.P., Bezawada, P., Kudrimoti, S., Wilder, P.T., Hartman, K.G., Godoy-Ruiz, R., Toth, E.A., Coop, A., MacKerell, A.D. and Weber, D.J. (2012) Structure-Based Discovery of a Novel Pentamidine-Related Inhibitor of the Calcium-Binding Protein S100B. ACS Med. Chem. Lett., 3(12): 975-9.
- Liriano MA, Varney KM, Wright NT, Hoffman CL, Toth EA, Ishima R, Weber DJ. (2012) Target Binding to S100B Reduces Dynamic Properties and Increases Ca(2+)-Binding Affinity for Wild Type and EF-Hand Mutant Proteins. J. Mol. Biol., 423(3):365-85
- Manvilla, BA, Maiti, A, Begley, MC, Toth, EA, and Drohat, AC. (2012) Crystal structure of human methyl-binding domain IV glycosylase bound to abasic DNA. J Mol. Biol., 420(3), 164-75.
- Bernstein, J. and Toth, E.A. (2012) Yeast Nuclear RNA Processing. World J. Biol. Chem., 3(1), 7-26.
- Luncsford, P.J., Chang, D-Y., Shi, G., Bernstein, J., Madabushi, A., Patterson, D.N., Lu, A-L., and Toth, E.A. (2010) A structural hinge in eukaryotic MutY homologues mediates catalytic activity and Rad9-Rad1-Hus1 checkpoint complex interactions. J. Mol. Biol., 403(3), 351-370. PMCID: PMC2953589.
- Zucconi BE, Ballin JD, Brewer BY, Ross CR, Huang J, Toth EA, Wilson GM. (2010) Alternatively expressed domains of AU-rich element RNA- binding protein 1 (AUF1) regulate RNA-binding affinity, RNA-induced protein oligomerization, and the local conformation of bound RNA ligands. J. Biol. Chem., 285(50), 39127-39. PMCID: PMC2998080.
- Ballin, J.D., Prevas, J.P., Ross, C.R., Toth, E.A., Wilson, G.M., Record M.T. (2010). Contributions of the histidine side chain and the N-terminal alpha-amino group to the binding thermodynamics of oligopeptides to nucleic acids as a function of pH. Biochemistry, 49, 2018-2030. PMCID: PMC2864607
- Bernstein J, Ballin JD, Patterson DN, Wilson GM, Toth EA. (2010). Unique properties of the Mtr4p-poly(A) complex suggest a role in substrate targeting. Biochemistry, 49(49),10357-70. PMCID: PMC2999651.
- Wilder, P.T., Charpentier, T.H., Liriano, M.A., Gianni, K., Varney, K.M., Pozharski, E., Coop, A., Toth, E.A., MacKerell, A.D., and Weber, D.J. (2010) In vitro screening and structural characterization of inhibitors of the S100B-p53 interaction. Int. J. High Throughput Screening, 2010(1), 109-126. PMCID: PMC2995924.
- Charpentier, T.H., Thompson, L.E., Liriano, M.A., Varney, K.M., Wilder, P.T., Pozharski, E., Toth, E.A., and Weber, D.J. (2010). The effect of the CapZ peptide (TRTK-12) binding to Ca2+-S100B as examined by NMR and X-ray crystallography, J Mol Biol, 396, 1227-1243. PMCID: PMC2843395.
- Charpentier, T.H., Wilder, P.T., Liriano, M.A., Varney, K.M., Zhong, S., Coop, A., Pozharski, E., MacKerell, A.D., Toth, E.A., and Weber, D.J. (2009). Small molecules bound to unique sites in the target protein binding cleft of calcium-bound S100B as characterized by nuclear magnetic resonance (NMR) and X-ray crystallography. Biochemistry, 48, 6202-6212. PMCID: PMC2804263.
- Charpentier, T.H., Wilder, P.T., Liriano, M., Varney, K.M., Pozharski, E., MacKerell, A.D., Coop, A., Toth, E.A., and Weber, D.J. (2008) Divalent metal ion complexes of S100B in the absence and presence of pentamidine. J Mol Biol, 382, 56-73. PMCID: PMC2636698.
- Bernstein, J., Patterson, D.N., Wilson, G.M., Toth, E.A. (2008) Characterization of the essential activities of Saccharomyces cerevisiae Mtr4p, A 3'→5' helicase partner of the nuclear exosome. J Biol Chem, 283(8), 4930-4942.
- Fialcowitz-White, E.J., Brewer, B.Y., Ballin, J.D., Willis, C.D., Toth, E.A., and Wilson, G.M. (2007). Specific protein domains mediate cooperative assembly of HuR oligomers on AU-rich mRNA-destabilizing sequences. J Biol Chem, 282(29), 20948-20959. PMCID: PMC2244793.