Multisite Phosphorylation Modulates the T Cell Receptor ζ-Chain Potency but not the Switchlike Response.
Multisite phosphorylation is ubiquitous in cellular signaling and is thought to provide signaling proteins with additional regulatory mechanisms. Indeed, mathematical models have revealed a large number of mechanisms by which multisite phosphorylation can produce switchlike responses. The T cell antigen receptor (TCR) is a multisubunit receptor on the surface of T cells that is a prototypical multisite substrate as it contains 20 sites that are distributed on 10 conserved immunoreceptor tyrosine-based activation motifs (ITAMs). The TCR ζ-chain is a homodimer subunit that contains six ITAMs (12 sites) and exhibits a number of properties that are predicted to be sufficient for a switchlike response. We have used cellular reconstitution to systematically study multisite phosphorylation of the TCR ζ-chain. We find that multisite phosphorylation proceeds by a nonsequential random mechanism, and find no evidence that multiple ITAMs modulate a switchlike response but do find that they alter receptor potency and maximum phosphorylation. Modulation of receptor potency can be explained by a reduction in molecular entropy of the disordered ζ-chain upon phosphorylation. We further find that the tyrosine kinase ZAP-70 increases receptor potency but does not modulate the switchlike response. In contrast to other multisite proteins, where phosphorylations act in strong concert to modulate protein function, we suggest that the multiple ITAMs on the TCR function mainly to amplify subsequent signaling.
Sir William Dunn School of Pathology, Mathematical Institute, University of Oxford, Oxfordshire, United Kingdom.
Himadri
H
Mukhopadhyay
Sir William Dunn School of Pathology, Mathematical Institute, University of Oxford, Oxfordshire, United Kingdom.
Ben
B
de Wet
Department of Mathematics, University of California-Irvine, Irvine, California.
Lara
L
Clemens
Wolfson Centre for Mathematical Biology, Mathematical Institute, University of Oxford, Oxfordshire, United Kingdom.
Philip K
PK
Maini
Department of Mathematics, University of California-Irvine, Irvine, California.
Jun
J
Allard
Sir William Dunn School of Pathology, Mathematical Institute, University of Oxford, Oxfordshire, United Kingdom. Electronic address: anton.vandermerwe@path.ox.ac.uk.
P Anton
PA
van der Merwe
Sir William Dunn School of Pathology, Mathematical Institute, University of Oxford, Oxfordshire, United Kingdom; Wolfson Centre for Mathematical Biology, Mathematical Institute, University of Oxford, Oxfordshire, United Kingdom. Electronic address: omer.dushek@path.ox.ac.uk.
Omer
O
Dushek
D000818:Animals; D057809:HEK293 Cells; D006801:Humans; D007700:Kinetics; D051379:Mice; D010766:Phosphorylation; D011948:Receptors, Antigen, T-Cell / Q000737:chemistry / Q000378:metabolism*
D011948:Receptors, Antigen, T-Cell; C054979:antigen T cell receptor, zeta chain