Different Thermodynamic Binding Mechanisms and Peptide Fine Specificities Associated with a Panel of Structurally Similar High-Affinity T Cell Receptors

Department of Biochemistry and School of Chemical Sciences Biocrystallization Service, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA.
Biochemistry (Impact Factor: 3.02). 11/2008; 47(47):12398-408. DOI: 10.1021/bi801349g
Source: PubMed


To understand the mechanisms that govern T cell receptor (TCR)-peptide MHC (pMHC) binding and the role that different regions of the TCR play in affinity and antigen specificity, we have studied the TCR from T cell clone 2C. High-affinity mutants of the 2C TCR that bind QL9-L(d) as a strong agonist were generated previously by site-directed mutagenesis of complementarity determining regions (CDRs) 1beta, 2alpha, 3alpha, or 3beta. We performed isothermal titration calorimetry to assess whether they use similar thermodynamic mechanisms to achieve high affinity for QL9-L(d). Four of the five TCRs examined bound to QL9-L(d) in an enthalpically driven, entropically unfavorable manner. In contrast, the high-affinity CDR1beta mutant resembled the wild-type 2C TCR interaction, with favorable entropy. To assess fine specificity, we measured the binding and kinetics of these mutants for both QL9-L(d) and a single amino acid peptide variant of QL9, called QL9-Y5-L(d). While 2C and most of the mutants had equal or higher affinity for the Y5 variant than for QL9, mutant CDR1beta exhibited 8-fold lower affinity for Y5 compared to QL9. To examine possible structural correlates of the thermodynamic and fine specificity signatures of the TCRs, the structure of unliganded QL9-L(d) was solved and compared to structures of the 2C TCR/QL9-L(d) complex and three high-affinity TCR/QL9-L(d) complexes. Our findings show that the QL9-L(d) complex does not undergo major conformational changes upon binding. Thus, subtle changes in individual CDRs account for the diverse thermodynamic and kinetic binding mechanisms and for the different peptide fine specificities.

Download full-text


Available from: Jennifer D Stone, Dec 03, 2014
46 Reads
  • Source
    • "Methods of statistical mechanics may successfully be applied in order to quantitatively understand the immune system [3] [4], and different modeling approaches are adequate for acquired immunity, as surveyed in a seminal paper by Perelson and Weisbush [5]. Modeling and simulation can be performed on different levels, starting at the top level with agent-based models [6] [7] for the cooperation of numerous large biomolecules in the formation of the immune synapse [8] [9] [10] [11] down to more detailed models of antigen binding [12], recognition, and signaling [13] [14] [15] [16] [17] [18] [19] [20]. T-cell proliferation modulated by interleukin 2 has been simulated [21]. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Molecular dynamics simulations have to be sufficiently long to draw reliable conclusions. However, no method exists to prove that a simulation has converged. We suggest the method of "lagged RMSD-analysis" as a tool to judge if an MD simulation has not yet run long enough. The analysis is based on RMSD values between pairs of configurations separated by variable time intervals Δt. Unless RMSD(Δt) has reached a stationary shape, the simulation has not yet converged.
    Computational and Mathematical Methods in Medicine 09/2012; 2012(1):173521. DOI:10.1155/2012/173521 · 0.77 Impact Factor
  • Source
    • "In the traditional view of TCR:pMHC binding, the CDR3 loops are the primary regions that interact with the peptide, conferring the cross-reactive property of T cells, and therefore have been the main focus in determining what makes a T cell potentially autoreactive (Reiser et al., 2003; Yin et al., 2011). A few additional studies have directly mutagenized CDR 1, 2, and 3 loops and seen large changes in antigen specificity (Jones et al., 2008; Zhao et al., 2007) and selection (Sim et al., 1996). With M2, mutations in the CDR1α loop not only generate a higher affinity TCR (Chlewicki et al., 2005) but also regulate activation through the TCR. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Changes in the peptide and MHC molecules have been extensively examined for how they alter T cell activation, but many fewer studies have examined the TCR. Structural studies of how TCR differences alter T cell specificity have focused on broad variation in the CDR3 loops. However, changes in the CDR1 and 2 loops can also alter TCR recognition of pMHC. In this study we focus on two mutations in the CDR1α loop of the TCR that increased the affinity of a TCR for agonist Hb(64-76)/I-E(k) by increasing the on-rate of the reaction. These same mutations also conferred broader recognition of altered peptide ligands. TCR transgenic mice expressing the CDR1α mutations had altered thymic selection, as most of the T cells were negatively selected compared to T cells expressing the wildtype TCR. The few T cells that escaped negative selection and were found in the periphery were rendered anergic, thereby avoiding autoimmunity. T cells with the CDR1α mutations were completely deleted in the presence of Hb(64-76) as an endogenous peptide. Interestingly, the wildtype T cells were not eliminated, identifying a threshold affinity for negative selection where a 3-fold increase in affinity is the difference between incomplete and complete deletion. Overall, these studies highlight how small changes in the TCR can increase the affinity of TCR:pMHC but with the consequences of skewing selection and producing an unresponsive T cell.
    Molecular Immunology 09/2012; 53(3):283-94. DOI:10.1016/j.molimm.2012.08.020 · 2.97 Impact Factor
  • Source
    • "The CDR that engage pMHC are not structurally fixed, interacting with pMHC in a "lock and key" manner. Rather they possess enormous flexibility and are able to conform to different pMHC structures (Hare et al., 1999; Jones et al., 2008; Wilson et al., 2004). Because of TCR degeneracy, it is estimated that a single receptor can bind as many as 10 6 distinct pMHC complexes. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Adoptive immunotherapy with tumor-specific T lymphocytes has demonstrated clinical benefit in some cancers, particularly melanoma. Yet isolating and expanding tumor-specific cells from patients is challenging and there is limited ability to control T-cell affinity and response characteristics. T-cell receptor (TCR) gene therapy, in which T lymphocytes for immunotherapy are redirected using an introduced rearranged TCR, has emerged as an important alternative. Successful TCR gene therapy requires consideration of a number of issues, including TCR specificity and affinity, optimal gene therapy constructs, types of T cells administered, and the survival and activity of the modified cells. In this review we highlight the rationale for and experience with TCR gene therapy as well as new approaches to enhancing it.
    Archivum Immunologiae et Therapiae Experimentalis 10/2010; 58(5):335-46. DOI:10.1007/s00005-010-0090-1 · 3.18 Impact Factor
Show more