PMID- 27114505 OWN - NLM STAT- MEDLINE DCOM- 20161213 LR - 20220129 IS - 1091-6490 (Electronic) IS - 0027-8424 (Print) IS - 0027-8424 (Linking) VI - 113 IP - 20 DP - 2016 May 17 TI - Remarkably low affinity of CD4/peptide-major histocompatibility complex class II protein interactions. PG - 5682-7 LID - 10.1073/pnas.1513918113 [doi] AB - The alphabeta 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 approximately 5,000 molecules/mum(2) 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. FAU - Jonsson, Peter AU - Jonsson P AD - Department of Chemistry, University of Cambridge, Cambridge CB2 1EW, United Kingdom; Department of Chemistry, Lund University, SE-22100 Lund, Sweden; FAU - Southcombe, Jennifer H AU - Southcombe JH AD - MRC Human Immunology Unit, University of Oxford, Oxford OX3 9DS, United Kingdom; Weatherall Institute of Molecular Medicine, University of Oxford, Oxford OX3 9DS, United Kingdom; Nuffield Department of Obstetrics and Gynaecology, University of Oxford, Oxford OX3 9DU, United Kingdom; FAU - Santos, Ana Mafalda AU - Santos AM AD - MRC Human Immunology Unit, University of Oxford, Oxford OX3 9DS, United Kingdom; Weatherall Institute of Molecular Medicine, University of Oxford, Oxford OX3 9DS, United Kingdom; FAU - Huo, Jiandong AU - Huo J AD - MRC Human Immunology Unit, University of Oxford, Oxford OX3 9DS, United Kingdom; Weatherall Institute of Molecular Medicine, University of Oxford, Oxford OX3 9DS, United Kingdom; FAU - Fernandes, Ricardo A AU - Fernandes RA AD - MRC Human Immunology Unit, University of Oxford, Oxford OX3 9DS, United Kingdom; Weatherall Institute of Molecular Medicine, University of Oxford, Oxford OX3 9DS, United Kingdom; FAU - McColl, James AU - McColl J AD - Department of Chemistry, University of Cambridge, Cambridge CB2 1EW, United Kingdom; FAU - Lever, Melissa AU - Lever M AD - Sir William Dunn School of Pathology, University of Oxford, Oxford OX1 3RE, United Kingdom; FAU - Evans, Edward J AU - Evans EJ AD - MRC Human Immunology Unit, University of Oxford, Oxford OX3 9DS, United Kingdom; Weatherall Institute of Molecular Medicine, University of Oxford, Oxford OX3 9DS, United Kingdom; FAU - Hudson, Alexander AU - Hudson A AD - MRC Human Immunology Unit, University of Oxford, Oxford OX3 9DS, United Kingdom; Weatherall Institute of Molecular Medicine, University of Oxford, Oxford OX3 9DS, United Kingdom; FAU - Chang, Veronica T AU - Chang VT AD - MRC Human Immunology Unit, University of Oxford, Oxford OX3 9DS, United Kingdom; Weatherall Institute of Molecular Medicine, University of Oxford, Oxford OX3 9DS, United Kingdom; FAU - Hanke, Tomas AU - Hanke T AD - MRC Human Immunology Unit, University of Oxford, Oxford OX3 9DS, United Kingdom; FAU - Godkin, Andrew AU - Godkin A AD - Department of Infection and Immunity, School of Medicine, Cardiff University, Cardiff CF14 4XN, United Kingdom; FAU - Dunne, Paul D AU - Dunne PD AD - Department of Chemistry, University of Cambridge, Cambridge CB2 1EW, United Kingdom; FAU - Horrocks, Mathew H AU - Horrocks MH AD - Department of Chemistry, University of Cambridge, Cambridge CB2 1EW, United Kingdom; FAU - Palayret, Matthieu AU - Palayret M AD - Department of Chemistry, University of Cambridge, Cambridge CB2 1EW, United Kingdom; FAU - Screaton, Gavin R AU - Screaton GR AD - MRC Human Immunology Unit, University of Oxford, Oxford OX3 9DS, United Kingdom; FAU - Petersen, Jan AU - Petersen J AD - Infection and Immunity Program and Department of Biochemistry and Molecular Biology, Biomedicine Discovery Institute, Monash University, Clayton, VIC 3800, Australia; Australian Research Council Centre of Excellence in Advanced Molecular Imaging, Monash University, Clayton, VIC 3800, Australia; FAU - Rossjohn, Jamie AU - Rossjohn J AD - Department of Infection and Immunity, School of Medicine, Cardiff University, Cardiff CF14 4XN, United Kingdom; Infection and Immunity Program and Department of Biochemistry and Molecular Biology, Biomedicine Discovery Institute, Monash University, Clayton, VIC 3800, Australia; Australian Research Council Centre of Excellence in Advanced Molecular Imaging, Monash University, Clayton, VIC 3800, Australia; FAU - Fugger, Lars AU - Fugger L AD - MRC Human Immunology Unit, University of Oxford, Oxford OX3 9DS, United Kingdom; Weatherall Institute of Molecular Medicine, University of Oxford, Oxford OX3 9DS, United Kingdom; Nuffield Department of Clinical Neurosciences, Division of Clinical Neurology, University of Oxford, Oxford OX3 9DS, United Kingdom. FAU - Dushek, Omer AU - Dushek O AD - Sir William Dunn School of Pathology, University of Oxford, Oxford OX1 3RE, United Kingdom; FAU - Xu, Xiao-Ning AU - Xu XN AD - MRC Human Immunology Unit, University of Oxford, Oxford OX3 9DS, United Kingdom; x.xu@imperial.ac.uk simon.davis@imm.ox.ac.uk dk10012@cam.ac.uk. FAU - Davis, Simon J AU - Davis SJ AD - MRC Human Immunology Unit, University of Oxford, Oxford OX3 9DS, United Kingdom; Weatherall Institute of Molecular Medicine, University of Oxford, Oxford OX3 9DS, United Kingdom; x.xu@imperial.ac.uk simon.davis@imm.ox.ac.uk dk10012@cam.ac.uk. FAU - Klenerman, David AU - Klenerman D AD - Department of Chemistry, University of Cambridge, Cambridge CB2 1EW, United Kingdom; x.xu@imperial.ac.uk simon.davis@imm.ox.ac.uk dk10012@cam.ac.uk. LA - eng GR - G0801508/MRC_/Medical Research Council/United Kingdom GR - MR/N023668/1/MRC_/Medical Research Council/United Kingdom GR - MC_UU_12010/4/MRC_/Medical Research Council/United Kingdom GR - G0600000/MRC_/Medical Research Council/United Kingdom GR - 095541/WT_/Wellcome Trust/United Kingdom GR - 078121/WT_/Wellcome Trust/United Kingdom GR - 100308/WT_/Wellcome Trust/United Kingdom GR - G0400720/MRC_/Medical Research Council/United Kingdom PT - Journal Article PT - Research Support, Non-U.S. Gov't DEP - 20160425 PL - United States TA - Proc Natl Acad Sci U S A JT - Proceedings of the National Academy of Sciences of the United States of America JID - 7505876 RN - 0 (CD4 Antigens) RN - 0 (HLA-A*24:02 antigen) RN - 0 (HLA-A24 Antigen) RN - 0 (HLA-DRB1 Chains) RN - 0 (HLA-DRB1*15:01 antigen) RN - 0 (Maltose-Binding Proteins) SB - IM MH - Binding Sites MH - CD4 Antigens/*chemistry/metabolism MH - HEK293 Cells MH - HLA-A24 Antigen/*chemistry/metabolism MH - HLA-DRB1 Chains/*chemistry/metabolism MH - Humans MH - Maltose-Binding Proteins/chemistry MH - Models, Molecular MH - Phosphorylation MH - Protein Binding MH - Protein Interaction Domains and Motifs MH - Protein Interaction Mapping MH - Protein Processing, Post-Translational MH - Protein Stability MH - Surface Plasmon Resonance PMC - PMC4878507 OTO - NOTNLM OT - T-cell activation OT - TCR phosphorylation OT - adhesion OT - binding equilibrium and kinetics OT - protein interactions COIS- The authors declare no conflict of interest. EDAT- 2016/04/27 06:00 MHDA- 2016/12/15 06:00 PMCR- 2016/11/17 CRDT- 2016/04/27 06:00 PHST- 2016/04/27 06:00 [entrez] PHST- 2016/04/27 06:00 [pubmed] PHST- 2016/12/15 06:00 [medline] PHST- 2016/11/17 00:00 [pmc-release] AID - 1513918113 [pii] AID - 201513918 [pii] AID - 10.1073/pnas.1513918113 [doi] PST - ppublish SO - Proc Natl Acad Sci U S A. 2016 May 17;113(20):5682-7. doi: 10.1073/pnas.1513918113. Epub 2016 Apr 25.