Todd Holyoak

Bachelor of Science (BSc) Waterloo, Doctor of Philosophy (PhD) Notre Dame

Email:  tholyoak@uwaterloo.ca

Telephone:  (519) 888-4567 ext. 31565

Office:  B1-276A

Lab:  (519) 888-4567 ext. 31559

Research interests

My laboratory’s research interests lie in the areas of enzyme structure, mechanism, inhibition and allostery. In light of these general interests our research currently focuses on the role that conformational plasticity plays in these areas of enzymology and how these dynamic aspects of enzyme structure can be exploited in the regulation of enzyme function. We are currently investigating these phenomena in two enzyme families:

1)    the GTP-dependent phosphoenolpyruvate carboxykinase and
2)    the IgA protease family of bacterial proteases

using primarily the tools of steady-state kinetics and x-ray crystallography.

Phoshoenolpyruvate Carboxykinases (PEPCK)

Our investigations of PEPCK utilize these enzymes as a model system in which to investigate and develop our understanding of the linkage between the conformational plasticity of protein structure and enzyme function and molecular recognition. However, our studies on PEPCK should have additional impacts upon human health as PEPCK is an important cataplerotic enzyme whose activity in humans and other mammals is essential to the maintenance of blood glucose levels.  As a consequence, flux through PEPCK contributes to the fasting hyperglycemia observed in individuals afflicted with either Type I or Type II diabetes.

IgA proteases

In the IgA proteases we are interested in discovering the mechanisms by which this enzyme family, containing both serine and metallo-protease isoforms, selectively cleaves a narrow range of protein substrates, primarily human immunoglobulin A1  (IgA1). In particular we are interested in how conformational flexibility plays a role in substrate selectivity and catalytic function in these enzymes. IgA proteases are produced in a number of important human bacterial pathogens, including Haemophilus influenzae and Streptococcus pneumoniae, and the evidence supports a definite role for IgA proteases in the pathogenesis of mucosal infection.

Recent publications

• Park KT, Wu W, Battaile KP, Lovell S, Holyoak T, Lutkenhaus J. (2011) The Min oscillator uses MinD-dependent conformational changes in MinE to spatially regulate cytokinesis. Cell.146(3):396-407.
• Wu W, Park KT, Holyoak T, Lutkenhaus J. (2011) Determination of the structure of the MinD-ATP complex reveals the orientation of MinD on the membrane and the relative location of the binding sites for MinE and MinC. Mol Microbiol. 79(6):1515-28. 
• Xia Z, Chibnik LB, Glanz BI, Liguori M, Shulman JM, Tran D, Khoury SJ, Chitnis T, Holyoak T, Weiner HL, Guttmann CR, De Jager PL. (2010) A putative Alzheimer's disease risk allele in PCK1 influences brain atrophy in multiple sclerosis. PLoS One.  5(11):e14169.
• Fenton AW, Johnson TA, Holyoak T. (2010) The pyruvate kinase model system, a cautionary tale for the use of osmolyte perturbations to support conformational equilibria in allostery. Protein Sci. 19(9):1796-800.
• Johnson TA, Holyoak T. (2010) Increasing the conformational entropy of the Omega-loop lid domain in phosphoenolpyruvate carboxykinase impairs catalysis and decreases catalytic fidelity. Biochemistry. 49(25):5176-87.
• Carlson GM, Holyoak T. (2009) Structural insights into the mechanism of phosphoenolpyruvate carboxykinase catalysis. J Biol Chem. 284(40):27037-41.
• Johnson TA, Qiu J, Plaut AG, Holyoak T. (2009) Active-site gating regulates substrate selectivity in a chymotrypsin-like serine protease the structure of Haemophilus influenzae immunoglobulin A1 protease. J Mol Biol.389(3):559-74. 
• Sullivan SM, Holyoak T. (2008) Enzymes with lid-gated active sites must operate by an induced fit mechanism instead of conformational selection. Proc Natl Acad Sci U S A. 105(37):13829-34. 
• Stiffin RM, Sullivan SM, Carlson GM, Holyoak T. (2008) Differential inhibition of cytosolic PEPCK by substrate analogues. Kinetic and structural characterization of inhibitor recognition. Biochemistry.47(7):2099-109.
• Sullivan SM, Holyoak T. (2007) Structures of rat cytosolic PEPCK: insight into the mechanism of phosphorylation and decarboxylation of oxaloacetic acid. Biochemistry. 46(35):10078-88.
• Wheatley JL, Holyoak T (2007) Differential P1 arginine and lysine recognition in the prototypical proprotein convertase Kex2.. Proc Natl Acad Sci U S A. 104(16):6626-31.