Cooperative Stabilization of Close-Contact Zones Leads to Sensitivity and Selectivity in T-Cell Recognition

T cells are sensitive to 1 to 10 foreign-peptide-MHC complexes among a vast majority of self-peptide-MHC complexes, and discriminate selectively between peptide-MHC complexes that differ not much in their binding affinity to T-cell receptors (TCRs). Quantitative models that aim to explain this sensitivity and selectivity largely focus on single TCR/peptide-MHC complexes, but T cell adhesion involves a multitude of different complexes. In this article, we demonstrate in a three-dimensional computational model of T-cell adhesion that the cooperative stabilization of close-contact zones is sensitive to one to three foreign-peptide-MHC complexes and occurs at a rather sharp threshold affinity of these complexes, which implies selectivity. In these close-contact zones with lateral extensions of hundred to several hundred nanometers, few TCR/foreign-peptide-MHC complexes and many TCR/self-peptide-MHC complexes are segregated from LFA-1/ICAM-1 complexes that form at larger membrane separations. Previous high-resolution microscopy experiments indicate that the sensitivity and selectivity in the formation of closed-contact zones reported here are relevant for T-cell recognition, because the stabilization of close-contact zones by foreign, agonist peptide-MHC complexes precedes T-cell signaling and activation in the experiments.

Cooperative Stabilization of Close-Contact Zones Leads to Sensitivity and Selectivity in T-Cell Recognition

T cells are sensitive to 1 to 10 foreign-peptide-MHC complexes among a vast majority of self-peptide-MHC complexes, and discriminate selectively between peptide-MHC complexes that differ not much in their binding affinity to T-cell receptors (TCRs). Quantitative models that aim to explain this sensitivity and selectivity largely focus on single TCR/peptide-MHC complexes, but T cell adhesion involves a multitude of different complexes. In this article, we demonstrate in a three-dimensional computational model of T-cell adhesion that the cooperative stabilization of close-contact zones is sensitive to 1 to 3 foreign-peptide-MHC complexes and occurs at a rather sharp threshold affinity of these complexes, which implies selectivity. In these close-contact zones with lateral extensions of hundred to several hundred nanometers, few TCR/foreign-peptide-MHC complexes and many TCR/self-peptide-MHC complexes are segregated from LFA-1/ICAM-1 complexes that form at larger membrane separations. Previous high-resolution microscopy experiments indicate that the sensitivity and selectivity in the formation of closed-contact zones reported here is relevant for T-cell recognition, because the stabilization of close-contact zones by foreign, agonist peptide-MHC complexes precedes T-cell signaling and activation in the experiments.

GFP fusion protein with embedded foreign peptide

From the point of view structural biology and protein engineering the green fluorescent protein (GFP) is an exceptionally attracting object. The tertiary structure of GFP is quite unique: it reminds a “cylinder” or a “barrel” consisting of beta-layers that contains an alpha-helix inside. The “barrel” is a special container for an alpha-helix serving to protect the latter from the influence of the surroundings. Therefore a reasonable question arises whether the “barrel” can function as a container for preservation and isolation of other peptides. The alpha-helix itself contains hydrophilic amino acids, whereas inside the barrel there are many molecules of bound water. We supposed that the central alpha-helix of green fluorescent protein could be substituted for foreign peptide. In this study we checked the possibility for creation of such a system on base of GFP, where the toxic peptide is isolated from the environment inside the protein. The modification of green fluorescent protein was carried out. An antimicrobial peptide was inserted into the central alpha-helix. The results of our experiments show that such a chimeric protein is compact, soluble and non-toxic for the producing cell culture, but its structure is destabilized. The obtained data show that the idea of use of green fluorescent proteins as a «container» for storing foreign peptides could be realized.

The intron-22–inverted F8 locus permits factor VIII synthesis: explanation for low inhibitor risk and a role for pharmacogenomics

Intron-22-inversion patients express the entire Factor VIII (FVIII)-amino-acid sequence intracellularly as 2 non-secreted polypeptides and have a positive “intracellular (I)-FVIII-CRM” status. Mutations conferring a positive I-FVIII-CRM status are associated with low inhibitor risk and are pharmacogenetically relevant because inhibitor risk may be affected by the nature of the therapeutic FVIII-protein (tFVIII), the affinity of any tFVIII-derived foreign peptide (tFVIII-fp) for any HLA class-II isomer (HLA-II) comprising individual major histocompatibility complex (MHC) repertoires, and the stability of any tFVIII-fp/HLA-II complex. We hypothesize that mutations conferring a completely or substantially negative I-FVIII-CRM status are pharmacogenetically irrelevant because inhibitor risk is high with any tFVIII and individual MHC repertoire.

A helix–coil transition induced by the metal ion interaction with a grafted iron-binding site of the CyaY protein family

An iron-binding motif EExxED from the first α-helical stretch of frataxin was grafted on a foreign peptide scaffold:KD= 1.9 ± 0.2 μM and 1 : 1 stoichiometry.

T cell activation enhancement by endogenous pMHC acts for both weak and strong agonists but varies with differentiation state

T cells are extremely sensitive in their ability to find minute amounts of antigenic peptide in the midst of many endogenous peptides presented on an antigen-presenting cell. The role of endogenous peptides in the recognition of foreign peptide and hence in T cell activation has remained controversial for CD8+ T cell activation. We showed previously that in a CD8+ T cell hybridoma, nonstimulatory endogenous peptides enhance T cell sensitivity to antigen by increasing the coreceptor function of CD8. However, others were not able to detect such enhancement in naive and activated CD8+ T cells. Here, we show that endogenous peptides substantially enhance the ability of T cells to detect antigen, an effect measurable by up-regulation of activation or maturation markers and by increased effector function. This enhancement is most pronounced in thymocytes, moderate in naive T cells, and mild in effector T cells. The importance of endogenous peptides is inversely proportional to the agonist activity of the stimulatory peptide presented. Unlike for CD4+ T cells, the T cell receptor of CD8+ T cells does not distinguish between endogenous peptides for their ability to enhance antigen recognition.