Molecular mechanism of selective recruitment of Syk kinases by the membrane antigen-receptor complex

J Biol Chem. 2011 Jul 22;286(29):25872-81. doi: 10.1074/jbc.M111.223321. Epub 2011 May 21.

Abstract

ZAP-70 and Syk are essential tyrosine kinases in intracellular immunological signaling. Both contain an inhibitory SH2 domain tandem, which assembles onto the catalytic domain. Upon binding to doubly phosphorylated ITAM motifs on activated antigen receptors, the arrangement of the SH2 domains changes. From available structures, this event is not obviously conducive to dissociation of the autoinhibited complex, yet it ultimately translates into kinase activation through a mechanism not yet understood. We present a comprehensive theoretical study of this molecular mechanism, using atomic resolution simulations and free-energy calculations, totaling >10 μs of simulation time. Through these, we dissect the microscopic mechanism coupling stepwise ITAM engagement and SH2 tandem structural change and reveal key differences between ZAP-70 and Syk. Importantly, we show that a subtle conformational bias in the inter-SH2 connector causes ITAM to bind preferentially to kinase-dissociated tandems. We thus propose that phosphorylated antigen receptors selectively recruit kinases that are uninhibited and that the resulting population shift in the membrane vicinity sustains signal transduction.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Motifs
  • Cell Membrane / metabolism*
  • Enzyme Stability
  • Intracellular Signaling Peptides and Proteins / chemistry*
  • Intracellular Signaling Peptides and Proteins / metabolism*
  • Molecular Dynamics Simulation*
  • Protein Binding
  • Protein-Tyrosine Kinases / chemistry*
  • Protein-Tyrosine Kinases / metabolism*
  • Receptors, Antigen / metabolism*
  • Substrate Specificity
  • Syk Kinase
  • Thermodynamics
  • ZAP-70 Protein-Tyrosine Kinase / metabolism
  • src Homology Domains*

Substances

  • Intracellular Signaling Peptides and Proteins
  • Receptors, Antigen
  • Protein-Tyrosine Kinases
  • Syk Kinase
  • ZAP-70 Protein-Tyrosine Kinase