Biology and structure of pMHC receptors functioning as mechanosensors in the [alpha][beta] T-cell lineage

点击翻译按钮获取中文摘要

OVERALL SUMMARY T lymphocytes utilized  T cell receptors (TCRs) to distinguish self versus non-self through recognition of sparse antigenic peptides bound to MHC molecules (pMHC) arrayed on antigen presenting cells (APC). Through remarkable specificity and digital sensitivity,  T lymphocytes can destroy host cells altered by viruses, other infectious pathogens or cancerous transformations while leaving normal cellular counterparts intact. Until recently, it was unclear how TCR discrimination was achieved, given a lack of somatic mutations of TCR genes to boost receptor-ligand affinity unlike with B cell receptors. Contrary to conventional ligand associations exemplified by antigen-antibody interactions, however, it is now evident that physical force plays a crucial role in non-equilibrium TCR-based T cell activation. Here we investigate the overarching hypothesis that  lineage receptors that recognize pMHC ligands, namely TCRs and preTCRs, function as mechanosensors, transducing biomechanical forces to impact thymocyte development as well as T cell antigen recognition and activation. Both TCRs and preTCRs utilize force to induce different receptor conformers associated with energized and non- energized states. Project 1 shall elucidate biophysical features driving TCR mechanosensing using paired single molecule and single cell measurements via optical tweezers (OT) to determine non-equilibrium dynamics and parameterization of energy landscapes under force. In turn, CD8 T cell responses such as antigen-specific in vitro triggering sensitivity and in vivo cellular proliferation, effector and memory T cell development will be assessed using TCR retrogenic mice. RNAseq analysis of various populations and single cells shall define the connection between force-dependent transcriptomes and physical load on TCR-pMHC bonds. Project 2 shall perform comparable OT biophysical studies on preTCRs and pMHC interactions using high throughput next generation sequencing (NGS) of DN3, DN4, DP large and DP small subsets to determine TCR repertoire changes in MHC-sufficient and MHC-deficient animals in vitro and in vivo. By determining  chain clonotypes that are selected or disallowed during thymocyte developmental progression upon interaction with specific single- chain pMHC ligands, coupled RNAseq analysis of thymocytes expressing those preTCRs, OT profiling, Molecular Dynamics (MD) and NMR and X-ray crystallography structural studies, the rules governing early thymic selection by pMHC shall be defined. Distinctions among  and TCR lineages with respect to mechanical force shall be similarly analyzed and compared. Project 3 shall develop cutting-edge NMR methods to reveal allosteric mechanisms of preTCR and TCR receptors upon pMHC ligation, characterizing major and minor state structures and kinetics of interconversion aided by the MD Core to enhance atomistic detailing. An Administrative Core (A), a Protein Production Core (B) and a MD Core (C) will assist all Projects to discern how force empowers  T lineage recognition of pMHC with basic and translational importance.