Biology subjects

Mallis, R. J.

Publications and source records attributed to Mallis, R. J..

3 recordsLinked to original sources

bioRxiv2023

Parsing digital or analogue TCR performance through piconewton forces

{beta} T-cell receptors (TCRs) recognize aberrant peptides bound to major histocompatibility complex molecules (pMHCs) on unhealthy cells, amplifying specificity and sensitivity through physical load placed on the TCR-pMHC bond during immunosurveillance. To understand this mechanobiology, TCRs stimulated by abundantly and sparsely arrayed epitopes (NP366-374 /Db and PA224-233/Db, respectively) following in vivo influenza A virus infection were studied with optical tweezers. While certain NP repertoire CD8 T lymphocytes require many ligands for activation, others are digital, needing just few. Conversely, all PA TCRs perform digitally, exhibiting pronounced bond lifetime increases through sustained, energizing volleys of structural transitioning. Optimal digital performance is superior in vivo, correlating with ERK phosphorylation, CD3 loss, and activation marker upregulation in vitro. Given neoantigen array paucity, digital TCRs are likely critical for immunotherapies. One Sentence SummaryQuality of ligand recognition in a T-cell repertoire is revealed through application of physical load on clonal T-cell receptor (TCR)-pMHC bonds

immunology↗

bioRxiv2023

Asymmetric framework motion of TCR alpha beta controls load-dependent peptide discrimination

Mechanical force is critical for the interaction between an {beta}T cell receptor (TCR) and a peptide-bound major histocompatibility complex (pMHC) molecule to initiate productive T-cell activation. However, the underlying mechanism remains unclear. We use all-atom molecular dynamics simulations to examine the A6 TCR bound to HLA-A*02:01 presenting agonist or antagonist peptides under different extensions to simulate the effects of applied load on the complex, elucidating their divergent biological responses. We found that TCR and {beta} chains move asymmetrically, which impacts the interface with pMHC, in particular the peptide-sensing CDR3 loops. For the wild-type agonist, the complex stabilizes in a load-dependent manner while antagonists destabilize it. Simulations of the C{beta} FG-loop deletion, which reduces the catch bond response, and simulations with in silico mutant peptides further support the observed behaviors. The present results highlight the combined role of interdomain motion, fluctuating forces, and interfacial contacts in determining the mechanical response and fine peptide discrimination by a TCR, thereby resolving the conundrum of nearly identical crystal structures of TCR{beta}-pMHC agonist and antagonist complexes.

biophysics↗

bioRxiv2022

Pre-T cell receptor Self-MHC Sampling Restricts Thymocyte Dedifferentiation

Summary paragraphProgramming T lymphocytes to distinguish self from non-self is a vital, multi-step process arising in the thymus1-4. Signalling through the pre-T cell receptor (preTCR), a CD3-associated heterodimer comprising an invariant pT chain and a clone-specific {beta} chain, constitutes a critical early checkpoint in thymocyte development within the {beta} T-cell lineage5, 6. Recent work demonstrates that preTCRs arrayed on double negative (DN) thymocytes, like {beta} TCRs appearing on double positive (DP) thymocytes, ligate peptides bound to MHC molecules (pMHC) on thymic stroma but via a different molecular docking strategy7-10. Here we show the consequences of those distinctive interactions for thymocyte progression, using synchronized fetal thymic progenitor cultures differing in the presence or absence of pMHC on support stroma, determining single cell transcriptomes at key thymocyte developmental transitions. Although MHC negative stroma fosters {beta} T lymphocyte differentiation, the absence of pMHC-preTCR interplay leads to deviant thymocyte transcriptional programming associated with de-differentiation. Highly proliferative DN and DP subsets with antecedent characteristics of T cell lymphoblastic and myeloid malignancies emerge. Thus, at least in vitro, beyond fostering {beta} chain repertoire broadening for subsequent {beta} TCR utilization, preTCR-pMHC interaction limits cellular plasticity to facilitate normal thymocyte differentiation and proliferation that, if absent, introduces significant developmental vulnerabilities.

immunology↗