Fluorine substitutions in an antigenic peptide selectively modulate T-cell receptor binding in a minimally perturbing manner.

TCR (T-cell receptor) recognition of antigenic peptides bound and presented by MHC (major histocompatibility complex) molecules forms the basis of the cellular immune response to pathogens and cancer. TCRs bind peptide-MHC complexes weakly and with fast kinetics, features which have hindered detailed biophysical studies of these interactions. Modified peptides resulting in enhanced TCR binding could help overcome these challenges.

Methods for quantifying T cell receptor binding affinities and thermodynamics.

αβ T cell receptors (TCRs) recognize peptide antigens bound and presented by class I or class II major histocompatibility complex (MHC) proteins. Recognition of a peptide/MHC complex is required for initiation and propagation of a cellular immune response, as well as the development and maintenance of the T cell repertoire. Here, we discuss methods to quantify the affinities and thermodynamics of interactions between soluble ectodomains of TCRs and their peptide/MHC ligands, focusing on titration calorimetry, surface plasmon resonance, and fluorescence anisotropy.

Conformational changes and flexibility in T-cell receptor recognition of peptide-MHC complexes.

A necessary feature of the immune system, TCR (T-cell receptor) cross-reactivity has been implicated in numerous autoimmune pathologies and is an underlying cause of transplant rejection. Early studies of the interactions of alphabeta TCRs (T-cell receptors) with their peptide-MHC ligands suggested that conformational plasticity in the TCR CDR (complementarity determining region) loops is a dominant contributor to T-cell cross-reactivity. Since these initial studies, the database of TCRs whose structures have been solved both bound and free is now large enough to permit general conclusions to be drawn about the extent of TCR plasticity and the types and locations of motion that occur.

Thermodynamics of T-cell receptor-peptide/MHC interactions: progress and opportunities.

alphabeta T-cell receptors (TCRs) recognize peptide antigens presented by class I or class II major histocompatibility complex molecules (pMHC). Here we review the use of thermodynamic measurements in the study of TCR-pMHC interactions, with attention to the diversity in binding thermodynamics and how this is related to the variation in TCR-pMHC interfaces. We show that there is no enthalpic or entropic signature for TCR binding; rather, enthalpy and entropy changes vary in a compensatory manner that reflects a narrow free energy window for the interactions that have been characterized.

Kinetics of thermal unfolding of phenylalanine hydroxylase variants containing different metal cofactors (FeII, CoII, and ZnII) and their isokinetic relationship.

The kinetics of thermal unfolding of apo- and holo-Chromobacterium violaceum phenylalanine hydroxylase (cPAH) was investigated using circular dichroism (CD) over the temperature range 44-76 degrees C. In addition to the native cofactor (FeII), the unfolding kinetics of holo-cPAH was characterized using ZnII and CoII as cofactors. Kinetic profiles for apo- and holo-cPAH showed a single-phase exponential rise in the CD signal at lambda=222 nm and a first-order dependence on protein concentration.

A comprehensive calorimetric investigation of an entropically driven T cell receptor-peptide/major histocompatibility complex interaction.

The alphabeta T cell receptor (TCR) is responsible for recognizing peptides bound and "presented" by major histocompatibility complex (MHC) molecules. We recently reported that at 25 degrees C the A6 TCR, which recognizes the Tax peptide presented by the class I MHC human leukocyte antigen-A*0201 (HLA-A2), binds with a weak DeltaH degrees , a favorable DeltaS degrees , and a moderately negative DeltaC(p). These observations were of interest given the unfavorable binding entropies and large heat capacity changes measured for many other TCR-ligand interactions, suggested to result from TCR conformational changes occurring upon binding.

Unraveling a hotspot for TCR recognition on HLA-A2: evidence against the existence of peptide-independent TCR binding determinants.

T cell receptor (TCR) recognition of peptide takes place in the context of the major histocompatibility complex (MHC) molecule, which accounts for approximately two-thirds of the peptide/MHC buried surface. Using the class I MHC HLA-A2 and a large panel of mutants, we have previously shown that surface mutations that disrupt TCR recognition vary with the identity of the peptide. The single exception is Lys66 on the HLA-A2 alpha1 helix, which when mutated to alanine disrupts recognition for 93% of over 250 different T cell clones or lines, independent of which peptide is bound.

Two different T cell receptors use different thermodynamic strategies to recognize the same peptide/MHC ligand.

A6 and B7 are two alphabeta T cell receptors (TCRs) that recognize the Tax peptide presented by the class I major histocompatibility molecule HLA-A2 (Tax/HLA-A2). Despite the fact that the two TCRs have different CDR loops and use different amino acid residues to contact their ligand, both receptors bind ligand with similar diagonal orientations. Here we show that they also bind with very similar binding affinities and kinetics (the DeltaDeltaG degrees for binding is approximately 0.

Proton transfer in gramicidin channels is modulated by the thickness of monoglyceride bilayers.

The thickness of monoglyceride planar bilayers has significant effects on the transfer of protons in both native gramicidin A (gA) and in covalently linked SS- and RR-dioxolane-linked gA proteins. Planar bilayers with various thicknesses were formed from an appropriate combination of monoglyceride with various fatty acid lengths and solvent. Bilayer thicknesses ranged from 25 A (monoolein in squalene) to 54 A (monoeicosenoin in decane).

On the origin of closing flickers in gramicidin channels: a new hypothesis.

The submillisecond closing events (flickers) and the single channel conductances to protons (g(H)) were studied in native gramicidin A (gA) and in the SS and RR diastereoisomers of dioxolane-linked gA channels in planar bilayers. Bilayers were formed from glycerylmonooleate (GMO) in various solvents. In GMO/decane (thick) bilayers, the largest flicker frequency occurred in the SS channel (39 s(-1)), followed by the RR (4 s(-1)) and native gA channels (3 s(-1)).