Sylvester Comprehensive Cancer Center

Thomas K. Harris, Ph.D.

Thomas K. Harris, Ph.D.

Associate Professor of Biochemistry & Molecular Biology

Description of Research

Since the overwhelming majority of protein kinase inhibitors bind in or near the ATP binding pocket shared by the catalytic domain of all kinases, very few serine-threonine protein kinase inhibitors have been clinically approved due to their broad specificity and overall high toxicity. Thus, Dr. Harris and his colleagues hypothesize that serine-threonine protein kinase inhibitor selectivity may be better achieved by designing compounds that target more distinguishing 'exosites'. Such binding events could serve to stabilize either (i) inactive kinase conformations or (ii) autoinhibitory domain-domain contacts formed between contiguous regulatory and catalytic kinase domains of multi-domain protein kinases. They are employing complementary approaches that seek to establish both the energetic and structural bases by which regulatory domains affect kinase activity. The foregoing approach is determination of the kinetic mechanisms of target protein kinases, which further focuses on establishing the degree of activation or inhibition that a regulatory domain exerts on one or more specific elementary reaction steps such as substrate binding or chemical phosphorylation. Subsequent elucidation of inhibitory contacts and domain-domain conformational dynamics that distinguish catalytically inactive and active kinases will facilitate design and discovery of the hypothesized highly selective 'exosite' inhibitors. The human serine-threonine protein kinases PDK1 and S6K1 serve as our model systems, as each enzyme is an established cancer drug discovery target that contains a single regulatory domain contiguous with the catalytic kinase domain. Recent research efforts have been aimed towards understanding how the (i) C-terminal pleckstrin homology (PH) domain of PDK1 and (ii) C-terminal autoinhibitory domain (AID) of S6K1 regulate kinase activation and reactivity, which is critical to tumor cell growth and metabolism.


  • Deduced kinetic mechanisms for (i) PDK1- and S6K1-catalyzed phosphorylation of model peptide substrates and (ii) PDK1-catalyzed phosphorylation and activation of S6K1
  • Deduced kinetic mechanisms by which the C-terminal PH and AID domains of PDK1 and S6K1 regulate kinase activation and reactivity
  • Developed protein engineering and spectroscopic methods for examining changes in orientation and contacts between regulatory and catalytic kinase domains

Selected Cancer-Related Publications

  • Keshwani MM, Gao X, Harris TK. Mechanism of PDK1-catalyzed Thr-229 Phosphorylation of the S6K1 Protein Kinase. J Biol Chem 284:22611-24, 2009. Read more »


Collaborating in the Multidisciplinary Research Program(s):

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