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T. J. Kappock

Biochemistry 

  • Assistant Professor of Biochemistry
765.494.8383
765.494.7897
BCHM Room 29

Lab Members


Area of Expertise: Resistance strategies in acetic acid bacteria; enzyme mechanism; purine biosynthesis

Biochemistry of acetic acid bacteria (AAB). Bacteria cope with life in harsh environments using specific stress responses and chemical alterations of cell components. The naturally acid-resistant AAB Acetobacter aceti has the ability to survive in molar concentrations of acetic acid at low pH. Most AAB are benign plant-associated organisms. Some strains produce huge amounts of acetic acid by oxidizing ethanol and have been used for millennia to make vinegar. These conditions poison other microbes, nearly all of which (unlike A. aceti) are unable to tolerate an acidic cytoplasm. We use this food-grade organism to explore bacterial acid survival strategies, which are among the most complicated stress responses deployed by microbes, including many pathogenic organisms. Our interests are centered on the adaptation of enzyme function and metabolism to acidic conditions. X-ray crystallographic studies of A. aceti proteins have revealed distinctive architectural features that are correlated with increased acid stability of pure proteins. 


Enzyme mechanism. Enzymes are the gold standard for synthetic chemistry. We are particularly interested in those that form carbon-carbon bonds, among them the purine biosynthesis enzyme PurE and the citric acid cycle enzyme citrate synthase. An example of this remarkable chemistry is the carbon dioxide migration performed by PurE (illustrated above for the microbial form of PurE). Structural, mutagenesis, and pre-steady state kinetics methods are enlisted to understand how these enzymes do their jobs. We typically use enzymes from A. aceti in these studies because they are durable and cooperative.


Selected Publications

Mullins, E. A., Sullivan, K. L., & Kappock, T. J. (2013). Function and X-Ray crystal structure of Escherichia coli YfdE. PLoS ONE, 8, e67901. doi: 10.1371/journal.pone.0067901. Retrieved from http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0067901

Mullins, E. A., & Kappock, T. J. (2013). Functional analysis of the acetic acid resistance (aar) gene cluster in Acetobacter aceti strain 1023. Acetic Acid Bacteria, s1, e3. Retrieved from http://www.pagepressjournals.org/index.php/aab/article/view/aab.2013.s1.e3

Mullins, E. A., & Kappock, T. J. (2012). Crystal structures of Acetobacter aceti succinyl-Coenzyme A (CoA):acetate CoA-transferase reveal specificity determinants and illustrate the mechanism used by class I CoA-transferases. Biochemistry, 42, 8422-8434. Retrieved from http://pubs.acs.org/doi/pdf/10.1021/bi300957f

Mullins, E. A., Starks, C. M., Francois, J. A., Sael, L., Kihara, D., & Kappock, T. J. (2012). Formyl-coenzyme A (CoA):oxalate CoA-transferase from the acidophile Acetobacter aceti has a distinctive electrostatic surface and inherent acid stability. Protein Sci., 21, 686-696. Retrieved from http://dx.doi.org/10.1002/pro.2054

Tranchimand, S., Starks, C. M., Mathews, I. I., Hockings, S. C., & Kappock, T. J. (2011). Treponema denticola PurE is a bacterial AIR carboxylase. Biochemistry, 50, 4623-4637. Retrieved from http://dx.doi.org/10.1021/bi102033a

Kurz, L. C., Constantine, C. Z., Jiang, H., & Kappock, T. J. (2009). The partial substrate dethiaacetyl-coenzyme A mimics all critical carbon acid reactions in the condensation half-reaction catalyzed by Thermoplasma acidophilum citrate synthase. Biochemistry, 48, 7878-7891. Retrieved from http://dx.doi.org/10.1021/bi9006447

Mullins, E. A., Francois, J. A., & Kappock, T. J. (2008). A specialized citric acid cycle requiring succinyl-coenzyme A (CoA):acetate CoA-transferase (AarC) confers acetic acid resistance on the acidophile Acetobacter aceti. J Bacteriol, 190, 4933-4940. Retrieved from http://dx.doi.org/10.1128/JB.00405-08

Francois, J. A., & Kappock, T. J. (2007). Alanine racemase from the acidophile Acetobacter aceti. Protein Expr. Purif., 51, 39-48. Retrieved from http://dx.doi.org/10.1016/j.pep.2006.05.016

Schaefer, J., Jiang, H., Ransome, A. E., & Kappock, T. J. (2007). Multiple active site histidine protonation states in Acetobacter aceti N5-carboxyaminoimidazole ribonucleotide mutase detected by REDOR NMR. Biochemistry, 46, 9507-9512. Retrieved from http://dx.doi.org/10.1021/bi700899q

Constantine, C. Z., Starks, C. M., Mill, C. P., Ransome, A. E., Karpowicz, S. J., Francois, J. A., . . . Kappock, T. J. (2006). Biochemical and structural studies of N5-carboxyaminoimidazole ribonucleotide mutase from the acidophilic bacterium Acetobacter aceti. Biochemistry, 45, 8193-8208. Retrieved from http://dx.doi.org/10.1021/bi060465n