The tautomerase superfamily, a group of structurally homologous proteins that share a common building block (the 2-1-2 motif) and a catalytic amino-terminal proline (Pro-1), is rich in mechanistic, structural, and evolutionary questions. The long-term goal of this project is to address these questions by a combination of mechanistic enzymology, molecular biology, X-ray crystallography, and bioinformatics. In the last funding period, mechanisms and structures were established for three superfamily members [the isomer-specific 3-chloroacrylic acid dehalogenases, designated CaaD and cis-CaaD, and malonate semialdehyde decarboxylase (MSAD)], showing how Nature used the 2-1-2 motif to create structural and mechanistic diversity. The stage is now set to use these enzymes as experimental vehicles to address fundamental questions about how enzymes work, how they evolve, and how new activities arise. The proposed studies will identify the underlying principles used in this system so that we might ultimately mimic Nature's processes and create new activities and structures using the 2-1-2 motif. Our major specific aims will be to (1) establish substrate orientation and interactions in the three active sites;(2) delineate the consequences of key mutations in CaaD, cis-CaaD, and MSAD;(3) carry out a pre-steady state kinetic analysis of CaaD and cis-CaaD;and (4) examine the role of catalytic promiscuity in the evolution of the tautomerase superfamily and establish evolutionary relationships by phylogenetic and bioinformatics analysis. The results set the stage for the generation of enzymatic activities using the 2-1-2 template. These studies will enhance our understanding of enzyme mechanisms and bacterial metabolism, lead to a better understanding of the role played by catalytic promiscuity in divergent evolution, and assist in the design of environmentally friendly proline-based biocatalysts. It is critical to understand how enzymes evolve due to the prevalence of antibiotic-resistant bacteria and other drug-resistant organisms (e.g., M. tuberculosis and HIV). One mechanism for resistance involves the enzymatic inactivation of a drug (e.g., 2-lactam hydrolysis). Resistance enzymes can evolve by amplification of a low-level resistance activity in a physiological enzyme. Thus, a well-defined model for divergent evolution is a valuable resource for understanding how resistance activities evolve in the first place and could suggest more effective strategies for overcoming drug-resistant organisms.

Public Health Relevance

It is critical to understand how enzymes evolve and acquire new functions due to the prevalence of antibiotic-resistant bacteria and other drug-resistant organisms such as M. tuberculosis and HIV. Drug-resistant organisms have become a major public health threat and will continue to be one. The proposed studies will result in a well-defined model for the evolution of enzymes and enhance our understanding of how resistance evolves in the first place.

National Institute of Health (NIH)
National Institute of General Medical Sciences (NIGMS)
Research Project (R01)
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Macromolecular Structure and Function E Study Section (MSFE)
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Barski, Oleg
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University of Texas Austin
Schools of Pharmacy
United States
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Huddleston, Jamison P; Wang, Susan C; Johnson, Kenneth A et al. (2017) Resolution of the uncertainty in the kinetic mechanism for the trans-3-Chloroacrylic acid dehalogenase-catalyzed reaction. Arch Biochem Biophys 623-624:9-19
Huddleston, Jamison P; Johnson Jr, William H; Schroeder, Gottfried K et al. (2015) Reactions of Cg10062, a cis-3-Chloroacrylic Acid Dehalogenase Homologue, with Acetylene and Allene Substrates: Evidence for a Hydration-Dependent Decarboxylation. Biochemistry 54:3009-23
Huddleston, Jamison P; Burks, Elizabeth A; Whitman, Christian P (2014) Identification and characterization of new family members in the tautomerase superfamily: analysis and implications. Arch Biochem Biophys 564:189-96
Schroeder, Gottfried K; Huddleston, Jamison P; Johnson Jr, William H et al. (2013) A mutational analysis of the active site loop residues in cis-3-Chloroacrylic acid dehalogenase. Biochemistry 52:4204-16
Poelarends, Gerrit J; Serrano, Hector; Huddleston, Jamison P et al. (2013) A mutational analysis of active site residues in trans-3-chloroacrylic acid dehalogenase. FEBS Lett 587:2842-50
Guo, Youzhong; Serrano, Hector; Poelarends, Gerrit J et al. (2013) Kinetic, mutational, and structural analysis of malonate semialdehyde decarboxylase from Coryneform bacterium strain FG41: mechanistic implications for the decarboxylase and hydratase activities. Biochemistry 52:4830-41
Huddleston, Jamison P; Schroeder, Gottfried K; Johnson, Kenneth A et al. (2012) A pre-steady state kinetic analysis of the ?Y60W mutant of trans-3-chloroacrylic acid dehalogenase: implications for the mechanism of the wild-type enzyme. Biochemistry 51:9420-35
Schroeder, Gottfried K; Johnson Jr, William H; Huddleston, Jamison P et al. (2012) Reaction of cis-3-chloroacrylic acid dehalogenase with an allene substrate, 2,3-butadienoate: hydration via an enamine. J Am Chem Soc 134:293-304
Guo, Youzhong; Serrano, Hector; Johnson Jr, William H et al. (2011) Crystal structures of native and inactivated cis-3-chloroacrylic acid dehalogenase: Implications for the catalytic and inactivation mechanisms. Bioorg Chem 39:1-9
Sevastik, Robin; Whitman, Christian P; Himo, Fahmi (2009) Reaction mechanism of cis-3-chloroacrylic acid dehalogenase: a theoretical study. Biochemistry 48:9641-9

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