Structural Features of the αβTCR Mechanotransduction Apparatus That Promote pMHC Discrimination

Brazin, Kristine N.; Mallis, Robert J.; Das, Dibyendu; Feng, Yuehan; Hwang, Wonmuk; Wang, Jia-Huai; Wagner, Gerhard; Lang, Matthew J.; Reinherz, Ellis L.

doi:10.3389/fimmu.2015.00441

Cited by 60 publications

(98 citation statements)

References 81 publications

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“…Furthermore, due to the 140° offset of the TCRα transmembrane domain charge residues that interact with CD3δε and CD3ζζ, too much adjustment would place CD4 closer to CD3ζζ than either CD3ε. The data presented here are compatible with models in which CD3δε and CD3γε are either situated on opposite sides of the TCR (22, 46), or reside on one side of the TCR such that the subunits are ordered δ:ε:ε:γ (1, 2, 16, 17). This last model is most consistent with other experimental data, as well as recent NMR data, so we currently consider it the best approximation of the subunit organization of the TCR-CD3 complex (1, 19).…”

Section: Discussionsupporting

confidence: 85%

The CD4 and CD3δε Cytosolic Juxtamembrane Regions Are Proximal within a Compact TCR–CD3–pMHC–CD4 Macrocomplex

Glassman

Parrish

Deshpande

et al. 2016

The Journal of Immunology

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T-cell receptors (TCRs) relay information about peptides embedded within major histocompatibility complex molecules (pMHC) to the immunoreceptor tyrosine-based activation motifs (ITAMs) of the associated CD3γε, CD3δε, and CD3ζζ signaling modules. CD4 then recruits the Src kinase, Lck, to the TCR-CD3 complex to phosphorylate the ITAMs, initiate intracellular signaling, and drive CD4+ T-cell fate decisions. While the six ITAMs of CD3ζζ are key determinants of T cell development, activation, and the execution of effector functions, multiple models predict that CD4 recruits Lck proximal to the four ITAMs of the CD3 heterodimers. We tested these models by placing FRET probes at the cytosolic juxtamembrane regions of CD4 and the CD3 subunits to evaluate their relationship upon pMHC engagement in mouse cell lines. The data are consistent with a compact assembly in which CD4 is proximal to CD3δε, CD3ζζ resides behind the TCR, and CD3γε is offset from CD3δε. These results advance our understanding of the architecture of the TCR-CD3-pMHC-CD4 macro-complex and point to regions of high CD4-Lck-ITAM concentrations therein. The findings thus have implications for TCR signaling, as phosphorylation of the CD3 ITAMs by CD4-associated Lck is important for CD4+ T-cell fate decisions.

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Section: Discussionsupporting

confidence: 85%

The CD4 and CD3δε Cytosolic Juxtamembrane Regions Are Proximal within a Compact TCR–CD3–pMHC–CD4 Macrocomplex

Glassman

Parrish

Deshpande

et al. 2016

The Journal of Immunology

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“…3 and SI Appendix, Figs. S4 and S9) (59,60). Stresses were applied experimentally via loading through our optical trap system, delivering, on average, ∼10 pN per TCR-pMHC interaction.…”

Section: Discussionmentioning

confidence: 99%

Mechanosensing drives acuity of αβ T-cell recognition

Feng

Brazin

Kobayashi

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

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156

197

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T lymphocytes use surface αβ T-cell receptors (TCRs) to recognize peptides bound to MHC molecules (pMHCs) on antigen-presenting cells (APCs). How the exquisite specificity of high-avidity T cells is achieved is unknown but essential, given the paucity of foreign pMHC ligands relative to the ubiquitous self-pMHC array on an APC. Using optical traps, we determine physicochemical triggering thresholds based on load and force direction. Strikingly, chemical thresholds in the absence of external load require orders of magnitude higher pMHC numbers than observed physiologically. In contrast, force applied in the shear direction (∼10 pN per TCR molecule) triggers T-cell Ca 2+ flux with as few as two pMHC molecules at the interacting surface interface with rapid positional relaxation associated with similarly directed motor-dependent transport via ∼8-nm steps, behaviors inconsistent with serial engagement during initial TCR triggering. These synergistic directional forces generated during cell motility are essential for adaptive T-cell immunity against infectious pathogens and cancers.mechanosensor | T-cell receptor | T-cell activation | optical tweezers | cellular force relaxation T he T-cell receptor (TCR) expressed on T lymphocytes of the adaptive immune system is a stout and squat (12-nm wide × 8-nm tall) multisubunit surface complex with a ligand binding moiety that is an αβ disulfide-linked heterodimer buttressed by the associated invariant CD3 subunits (1-3). The αβ chains are each encoded by V and J gene segments and in the case of the β, a D segment as well (4). The clone-specific TCR unique to each T lymphocyte endows mammals with the capacity to detect perturbations in host cellular function resulting from myriad infectious pathogens, physical damage (thermal, irradiation, etc.), or premalignant or malignant cellular transformations while averting strong self-reactivities that could induce autoimmunity (5).Signaling is initiated through ligation of the clonotype by its cognate antigenic peptide bound to an MHC molecule (pMHC) and displayed on the surface of antigen-presenting cells (APCs) (6, 7). Ligation impacts disposition and function of the associated CD3 dimers (CD3 γ, CD3 δ, and CD3ζζ) as well as the transmembrane domains of the TCR heterodimer and CD3 subunits that interdigitate in the membrane to signal into the cytoplasm (8, 9). A cascade of intracellular events involving phosphorylation of immunoreceptor tyrosine-based activation motifs (ITAMs) on the CD3 cytoplasmic domains with subsequent ZAP70 activation and downstream signaling follows (10, 11). Membrane-associated CD8 and CD4 coreceptors, marking cytotoxic T lymphocytes (CTLs) and helper T cells, respectively, function to bring the membrane-anchored Src family tyrosine kinase Lck to the TCR-pMHC complex for the initiation of ITAM phosphorylation. Signaling, in turn, leads to a transient rise of cytosolic Ca 2+ and other biochemical events resulting in transcriptional activation, ultimately resulting in developmental decisions or effector functi...

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“…The relevance of structural transitions in TCR signal initiation is an area of active research, and the recently recognized role for force in generating TCR-mediated responses (2, 4, 54-56) requires a mechanistic explanation of how force transmission to the cytoplasmic signaling domains is achieved. The potential involvement of changes in TM orientation in this process has been proposed by several groups (13)(14)(15)36), but the first direct experimental test of a TM change model comes from the recent work of Lee et al (17), who applied three different proximity-based techniques to document a ligand-induced change in the distance between the membrane-proximal intracellular ends of the two chains within a ζζ dimer. The nature of upstream structural changes that may trigger this mechanical switch was not experimentally addressed in this study, but our data suggest that alterations in the TCRαβ TM structure could be directly communicated to some or all of the signaling modules at the level of TM helix interactions.…”

Section: Discussionmentioning

confidence: 99%

“…Changes in the structured extracellular (EC) domains are proposed to translate, through an unknown mechanism, into alterations in the CD3 and ζζ cytoplasmic tails, converting them to a conformation that is receptive to phosphorylation by Lck and binding of other proximal signaling components (7)(8)(9)(10)(11)(12). This type of signaling model implies a pathway between EC and cytoplasmic domains that may involve alterations in the subunit transmembrane (TM) domains with respect to each other and/ or the lipid bilayer (13)(14)(15)(16). Consistent with this view, Kuhns and colleagues (17) recently reported a ligand-induced change in intersubunit proximity at the TM-juxtamembrane juncture in the ζζ dimer and proposed that this "mechanical switch" is coupled to signal initiation at the ζζ cytoplasmic tails.…”

mentioning

confidence: 99%

A conserved αβ transmembrane interface forms the core of a compact T-cell receptor–CD3 structure within the membrane

Krshnan

Park

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

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The T-cell antigen receptor (TCR) is an assembly of eight type I single-pass membrane proteins that occupies a central position in adaptive immunity. Many TCR-triggering models invoke an alteration in receptor complex structure as the initiating event, but both the precise subunit organization and the pathway by which ligandinduced alterations are transferred to the cytoplasmic signaling domains are unknown. Here, we show that the receptor complex transmembrane (TM) domains form an intimately associated eighthelix bundle organized by a specific interhelical TCR TM interface. The salient features of this core structure are absolutely conserved between αβ and γδ TCR sequences and throughout vertebrate evolution, and mutations at key interface residues caused defects in the formation of stable TCRαβ:CD3δe:CD3γe:ζζ complexes. These findings demonstrate that the eight TCR-CD3 subunits form a compact and precisely organized structure within the membrane and provide a structural basis for further investigation of conformationally regulated models of transbilayer TCR signaling.T-cell receptor | transmembrane structure | NMR | MD simulation | cysteine cross-linking T he antigen-specific T-cell response depends critically upon the ability of the T-cell receptor (TCR) to signal the recognition of activating ligands. The variable TCR proteins (α, β, δ, and γ) that bind to these ligands have no intrinsic intracellular signaling capability and transmit information through the noncovalently associated CD3δe, CD3γe, and ζζ modules containing cytoplasmic immunoreceptor tyrosine-based activation motifs (ITAMs) that are phosphorylated by the Src-family kinase Lck. The mechanism by which antigen sensing is translated from ligand binding at the distal end of the TCR to phosphorylation events at the cytoplasmic tails of the associated signaling modules remains an important open question in T-cell biology. A mounting pool of evidence implicates ligand-induced alterations in receptor structure (1) and/or TCR-CD3 configuration (2-6) as the triggering event. Changes in the structured extracellular (EC) domains are proposed to translate, through an unknown mechanism, into alterations in the CD3 and ζζ cytoplasmic tails, converting them to a conformation that is receptive to phosphorylation by Lck and binding of other proximal signaling components (7-12). This type of signaling model implies a pathway between EC and cytoplasmic domains that may involve alterations in the subunit transmembrane (TM) domains with respect to each other and/ or the lipid bilayer (13-16). Consistent with this view, Kuhns and colleagues (17) recently reported a ligand-induced change in intersubunit proximity at the TM-juxtamembrane juncture in the ζζ dimer and proposed that this "mechanical switch" is coupled to signal initiation at the ζζ cytoplasmic tails. However, the nature of the upstream structural changes that trigger this switch, and whether it is required for signal initiation, remain to be determined. Tracing possible transbilayer conformational pathway...

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Structural Features of the αβTCR Mechanotransduction Apparatus That Promote pMHC Discrimination

Cited by 60 publications

References 81 publications

The CD4 and CD3δε Cytosolic Juxtamembrane Regions Are Proximal within a Compact TCR–CD3–pMHC–CD4 Macrocomplex

The CD4 and CD3δε Cytosolic Juxtamembrane Regions Are Proximal within a Compact TCR–CD3–pMHC–CD4 Macrocomplex

Mechanosensing drives acuity of αβ T-cell recognition

A conserved αβ transmembrane interface forms the core of a compact T-cell receptor–CD3 structure within the membrane

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