CLEC-2 activates Syk through dimerization.
The C-type lectin receptor CLEC-2 activates platelets through Src and Syk tyrosine kinases, leading to tyrosine phosphorylation of downstream adapter proteins and effector enzymes, including phospholipase-C gamma2. Signaling is initiated through phosphorylation of a single conserved tyrosine located in a YxxL sequence in the CLEC-2 cytosolic tail. The signaling pathway used by CLEC-2 shares many similarities with that used by receptors that have 1 or more copies of an immunoreceptor tyrosine-based activation motif, defined by the sequence Yxx(L/I)x(6-12)Yxx(L/I), in their cytosolic tails or associated receptor chains. Phosphorylation of the conserved immunoreceptor tyrosine-based activation motif tyrosines promotes Syk binding and activation through binding of the Syk tandem SH2 domains. In this report, we present evidence using peptide pull-down studies, surface plasmon resonance, quantitative Western blotting, tryptophan fluorescence measurements, and competition experiments that Syk activation by CLEC-2 is mediated by the cross-linking through the tandem SH2 domains with a stoichiometry of 2:1. In support of this model, cross-linking and electron microscopy demonstrate that CLEC-2 is present as a dimer in resting platelets and converted to larger complexes on activation. This is a unique mode of activation of Syk by a single YxxL-containing receptor.
Centre for Cardiovascular Sciences, Institute for Biomedical Research, College of Medical and Dental Sciences, University of Birmingham, Birmingham, UK.
Craig E
CE
Hughes
Alice Y
AY
Pollitt
Jun
J
Mori
Johannes A
JA
Eble
Michael G
MG
Tomlinson
John H
JH
Hartwig
Christopher A
CA
O'Callaghan
Klaus
K
Fütterer
Steve P
SP
Watson
D020816:Amino Acid Motifs; D001792:Blood Platelets / Q000378:metabolism*; D004789:Enzyme Activation / Q000502:physiology; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000378:metabolism*; D037181:Lectins, C-Type / Q000378:metabolism*; D008562:Membrane Glycoproteins / Q000378:metabolism*; D051966:Phospholipase C gamma / Q000378:metabolism; D015539:Platelet Activation / Q000502:physiology*; D055503:Protein Multimerization / Q000502:physiology*; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology*; D000072377:Syk Kinase; D018909:src Homology Domains
C104778:CLEC2B protein, human; D047908:Intracellular Signaling Peptides and Proteins; D037181:Lectins, C-Type; D008562:Membrane Glycoproteins; D011505:Protein-Tyrosine Kinases; C000606896:SYK protein, human; D000072377:Syk Kinase; D051966:Phospholipase C gamma