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Activation Loop Dynamics Determine the Different Catalytic Efficiencies of B Cell– and T Cell–Specific Tec Kinases
Science Signaling
  • Raji E. Joseph, Iowa State University
  • Iivari Kleino, University of Massachusetts Medical School
  • Thomas E. Wales, Northeastern University
  • Qian Xie, Iowa State University
  • D. Bruce Fulton, Iowa State University
  • John R. Engen, Northeastern University
  • Leslie J. Berg, University of Massachusetts Medical School
  • Amy H. Andreotti, Iowa State University
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Itk and Btk are nonreceptor tyrosine kinases of the Tec family that signal downstream of the T cell receptor (TCR) and B cell receptor (BCR), respectively. Despite their high sequence similarity and related signaling roles, Btk is a substantially more active kinase than Itk. We showed that substitution of six of the 619 amino acid residues of Itk with those of Btk was sufficient to completely switch the activities of Itk and Btk. The substitutions responsible for the swap in activity are all localized to the activation segment of the kinase domain. Nuclear magnetic resonance and hydrogen-deuterium exchange mass spectrometry analyses revealed that Itk and Btk had distinct protein dynamics in this region, which could explain the observed differences in catalytic efficiency between these kinases. Introducing Itk with enhanced activity into T cells led to enhanced and prolonged TCR signaling compared to that in cells with wild-type Itk. These findings imply that evolutionary pressures have led to Tec kinases having distinct enzymatic properties depending on the cellular context. We suggest that the weaker catalytic activities observed for T cell–specific kinases is one mechanism to regulate cellular activation and prevent aberrant immune responses.


This is the author’s version of the work. It is posted here by permission of the AAAS for personal use, not for redistribution. The definitive version was published in Science Signaling on vol. 6 (2013), DOI: 10.1126/scisignal.2004298.

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American Association for the Advancement of Science
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Raji E. Joseph, Iivari Kleino, Thomas E. Wales, Qian Xie, et al.. "Activation Loop Dynamics Determine the Different Catalytic Efficiencies of B Cell– and T Cell–Specific Tec Kinases" Science Signaling Vol. 6 Iss. 290 (2013) p. ra76
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