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Remarkably low affinity of CD4/peptide-major histocompatibility complex class II protein interactions

Jönsson, Peter LU ; Southcombe, Jennifer H.; Mafalda Santos, Ana; Huo, Jiandong; Fernandes, Ricardo A.; McColl, James; Lever, Melissa; Evans, Edward J.; Hudson, Alexander and Chang, Veronica T., et al. (2016) In Proceedings of the National Academy of Sciences of the United States of America 113(20). p.5682-5687
Abstract

The αβ T-cell coreceptor CD4 enhances immune responses more than 1 million-fold in some assays, and yet the affinity of CD4 for its ligand, peptide-major histocompatibility class II (pMHC II) on antigen-presenting cells, is so weak that it was previously unquantifiable. Here, we report that a soluble form of CD4 failed to bind detectably to pMHC II in surface plasmon resonance-based assays, establishing a new upper limit for the solution affinity at 2.5 mM. However, when presented multivalently on magnetic beads, soluble CD4 bound pMHC II-expressing B cells, confirming that it is active and allowing mapping of the native coreceptor binding site on pMHC II. Whereas binding was undetectable in solution, the affinity of the CD4/pMHC II... (More)

The αβ T-cell coreceptor CD4 enhances immune responses more than 1 million-fold in some assays, and yet the affinity of CD4 for its ligand, peptide-major histocompatibility class II (pMHC II) on antigen-presenting cells, is so weak that it was previously unquantifiable. Here, we report that a soluble form of CD4 failed to bind detectably to pMHC II in surface plasmon resonance-based assays, establishing a new upper limit for the solution affinity at 2.5 mM. However, when presented multivalently on magnetic beads, soluble CD4 bound pMHC II-expressing B cells, confirming that it is active and allowing mapping of the native coreceptor binding site on pMHC II. Whereas binding was undetectable in solution, the affinity of the CD4/pMHC II interaction could be measured in 2D using CD4- and adhesion molecule-functionalized, supported lipid bilayers, yielding a 2D Kd of ∼5,000 molecules/μm2. This value is two to three orders of magnitude higher than previously measured 2D Kd values for interacting leukocyte surface proteins. Calculations indicated, however, that CD4/pMHC II binding would increase rates of T-cell receptor (TCR) complex phosphorylation by threefold via the recruitment of Lck, with only a small, 2-20% increase in the effective affinity of the TCR for pMHC II. The affinity of CD4/pMHC II therefore seems to be set at a value that increases T-cell sensitivity by enhancing phosphorylation, without compromising ligand discrimination.

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published
subject
keywords
Adhesion, Binding equilibrium and kinetics, Protein interactions, T-cell activation, TCR phosphorylation
in
Proceedings of the National Academy of Sciences of the United States of America
volume
113
issue
20
pages
6 pages
publisher
National Acad Sciences
external identifiers
  • scopus:84969786276
  • wos:000375977600057
ISSN
0027-8424
DOI
10.1073/pnas.1513918113
language
English
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yes
id
cb93631a-5054-4a9b-af3b-9edf38f108cf
date added to LUP
2017-01-30 11:17:22
date last changed
2017-09-18 11:34:45
@article{cb93631a-5054-4a9b-af3b-9edf38f108cf,
  abstract     = {<p>The αβ T-cell coreceptor CD4 enhances immune responses more than 1 million-fold in some assays, and yet the affinity of CD4 for its ligand, peptide-major histocompatibility class II (pMHC II) on antigen-presenting cells, is so weak that it was previously unquantifiable. Here, we report that a soluble form of CD4 failed to bind detectably to pMHC II in surface plasmon resonance-based assays, establishing a new upper limit for the solution affinity at 2.5 mM. However, when presented multivalently on magnetic beads, soluble CD4 bound pMHC II-expressing B cells, confirming that it is active and allowing mapping of the native coreceptor binding site on pMHC II. Whereas binding was undetectable in solution, the affinity of the CD4/pMHC II interaction could be measured in 2D using CD4- and adhesion molecule-functionalized, supported lipid bilayers, yielding a 2<sub>D</sub> Kd of ∼5,000 molecules/μm<sup>2</sup>. This value is two to three orders of magnitude higher than previously measured 2D K<sub>d</sub> values for interacting leukocyte surface proteins. Calculations indicated, however, that CD4/pMHC II binding would increase rates of T-cell receptor (TCR) complex phosphorylation by threefold via the recruitment of Lck, with only a small, 2-20% increase in the effective affinity of the TCR for pMHC II. The affinity of CD4/pMHC II therefore seems to be set at a value that increases T-cell sensitivity by enhancing phosphorylation, without compromising ligand discrimination.</p>},
  author       = {Jönsson, Peter and Southcombe, Jennifer H. and Mafalda Santos, Ana and Huo, Jiandong and Fernandes, Ricardo A. and McColl, James and Lever, Melissa and Evans, Edward J. and Hudson, Alexander and Chang, Veronica T. and Hanke, Tomáš and Godkin, Andrew and Dunne, Paul D. and Horrocks, Mathew H. and Palayret, Matthieu and Screaton, Gavin R. and Petersen, Jan and Rossjohn, Jamie and Fugger, Lars and Dushek, Omer and Xu, Xiao Ning and Davis, Simon J. and Klenerman, David},
  issn         = {0027-8424},
  keyword      = {Adhesion,Binding equilibrium and kinetics,Protein interactions,T-cell activation,TCR phosphorylation},
  language     = {eng},
  month        = {05},
  number       = {20},
  pages        = {5682--5687},
  publisher    = {National Acad Sciences},
  series       = {Proceedings of the National Academy of Sciences of the United States of America},
  title        = {Remarkably low affinity of CD4/peptide-major histocompatibility complex class II protein interactions},
  url          = {http://dx.doi.org/10.1073/pnas.1513918113},
  volume       = {113},
  year         = {2016},
}