Biology subjects

Choi, H.-K.

Publications and source records attributed to Choi, H.-K..

7 recordsLinked to original sources

bioRxiv2026

Visualizing immunoreceptor forces and their effects in vivo

Immunoreceptors experience forces that modulate their activities; however, demonstrating this in vivo has been limited by technical challenges. As a first step toward meeting this challenge, we adapted a synthetic Notch (SynNotch) receptor system to report force transmission through immunoreceptors in vivo by replacing the native ligand-binding domain with a receptor-specific antibody and rewiring Notch signaling to drive EGFP or luciferase expression. We expressed SynNotch on Jurkat cells targeting CD40 or T cell receptor (TCR) and characterized their activation in coculture with B or T cells, defining the requirements, optimal conditions, and kinetics of activation. Using complementary mechanobiology approaches, we quantified the exogenous force required for reporter activation and verified that activation depends on forces generated by receptor-expressing sender cells rather than SynNotch-expressing receiver cells. By implanting sensors and targets into immunocompromised mice, we visualized mechanically activated reporter expression on CD40 and TCR-targeting SynNotch cells in vivo. Furthermore, CD40 and TCR signaling was amplified when the receptor bore force against mechanical support from immobilized ligand, indicating that force functions as biologically relevant co-stimulus. Together, our results establish mechanically activated SynNotch reporters as a useful strategy for detecting receptor-associated mechanical signaling across 2D coculture, 3D organoid, and in vivo systems.

bioengineering↗

bioRxiv2025

Evaluating the effects of CD8/CD4 on T cell function in terms of TCR-pMHC-coreceptor catch and slip bonds

BackgroundT cells interact with peptide-major histocompatibility complex (pMHC) via the T cell receptor (TCR) and coreceptor CD4 or CD8 depending on the MHC class. These interactions form catch and slip bonds depending on the pMHC activity. Coreceptors and bond profiles impact TCR triggering and antigen discrimination. MethodsBuilt upon our recent correlative analysis of TCR-pMHC catch bond with T cell function, we analyzed 26 pairs of T-cell-pMHC interactions to compare the correlations of their biophysical metrics with antigen-induced T cell responses in two situations: when the coreceptor is prevented vs permitted to bind pMHC. ResultsWe found that the force-based metrics of TCR bond with pMHC perform better than parameters measured in the absence of force either in situ at the T cell membrane or in fluid phase using purified ectodomain proteins as predictors of T cell activation and thymocyte selection in both cases when the contributions of coreceptors are absent and present. Moreover, CD8 or CD4 co-engagement with pMHC systematically increases these metrics and increases TCR sensitivity and specificity, indicating coreceptor-mediated amplification of, or conversion to, catch-bonds that enhances mechanical tuning of TCR responses. ConclusionOur findings highlight the importance of force in antigen recognition by the TCR and reveal that parameters derived from the bond profile, especially in the presence of coreceptor, are more informative predictors of T cell activation compared to conventional affinity-based measurements. These results offer mechanistic insights into the roles of catch bonds and coreceptors in TCR antigen recognition.

immunology↗

bioRxiv2023

Mechanotransduction governs CD40 function and underlies X-linked Hyper IgM syndrome

B cell maturation in germinal centers (GCs) depends on cognate interactions between the T and B cells. Upon interaction with CD40 ligand (CD40L) on T cells, CD40 delivers co-stimulatory signals alongside B cell antigen receptor (BCR) signaling to regulate affinity maturation and antibody class-switch during GC reaction. Mutations in CD40L disrupt interactions with CD40, which lead to abnormal antibody responses in immune deficiencies known as X-linked Hyper IgM syndrome (X-HIgM). Assuming that physical interactions between highly mobile T and B cells generate mechanical forces on CD40-CD40L bonds, we set out to study the B cell mechanobiology mediated by CD40-CD40L interaction. Using a suite of biophysical assays we find that CD40 forms catch bond with CD40L where the bond lasts longer at larger forces, B cells exert tension on CD40-CD40L bonds, and force enhances CD40 signaling and antibody class-switch. Significantly, X-HIgM CD40L mutations impair catch bond formation, suppress endogenous tension, and reduce force-enhanced CD40 signaling, leading to deficiencies in antibody class switch. Our findings highlight the critical role of mechanotransduction in CD40 function and provide insights into the molecular mechanisms underlying X-HIgM syndrome.

immunology↗

bioRxiv2022

Memory in Repetitive Protein-Protein Interaction Series -- in Memory of the Late Professor Robert M. Nerem

Over the past three decades, the senior author had interacted with and been mentored by the late Professor Robert M. Nerem. In his memory, the authors summarized several observations made, ideas conceptualized, and mathematical models developed during this period for quantitatively analyzing memory effects in repetitive protein-protein interactions (PPI). Interactions between proteins in an organism coordinate its biological processes and may impact its responses to changing environment and diseases through feedback systems. Feedback systems function by using changes in the past to influence behaviors in the future, which we refer here as memory. Specifically, we consider how proteins on cell or in isolation retain information about prior interactions to impact current interactions. The micropipette, biomembrane force probe and atomic force microscopic techniques were used to repeatedly assay several PPIs. The resulting time series were analyzed by a previous and two new models to extract three memory indices of short (seconds), intermediate (minutes), and long (hours) timescales. We found that interactions of cell membrane, but not soluble, T cell receptor (TCR) with peptide-major histocompatibility complex (pMHC) exhibits short-term memory that impacts on-rate, but not off-rate of the binding kinetics. Peptide dissociation from MHC resulted in intermediate- and long-term memories in TCR-pMHC interactions. However, we observed no changes in kinetic parameters by repetitive measurements on living cells over intermediate timescale using stable pMHCs. Parameters quantifying memory effects in PPIs could provide additional information regarding biological mechanisms. The methods developed herein also provide tools for future research.

biophysics↗

bioRxiv2022

Catch bond models explain how force amplifies TCR signaling and antigen discrimination

Central to T cell biology, the T cell receptor (TCR) integrates forces in its triggering process upon interaction with peptide-major histocompatibility complex (pMHC)1-3. Phenotypically, forces elicit TCR catch-slip bonds with strong pMHCs but slip-only bonds with weak pMHCs4-10. While such correlation is commonly observed, the quantitative bond pattern and degree of "catchiness" vary. We developed two models based on the structure, elastic properties, and force-induced conformational changes of the TCR-pMHC-I/II complexes to derive from their bond characteristics more intrinsic parameters that underlie structural mechanisms, predict T cell signaling, and discriminate antigens. Applying the models to 55 datasets of 12 {beta}TCRs and their mutants interacting with corresponding pMHCs without coreceptor engagement demonstrated the ability for structural and physical parameters to quantitatively integrate and classify a broad range of bond behaviors and biological activities. Comparing to the generic two-state model for catch-slip bond that also fits the data, our models can distinguish class I from class II MHC systems and their best-fit parameters correlate with the TCR/pMHC potency to trigger T cell activation, which the generic model cannot. The models were tested by mutagenesis using structural analysis, bond profile measurement, and functional assay of a MHC and a TCR mutated to alter conformation changes. The extensive comparisons between theory and experiment provided strong validation of the models and testable hypothesis regarding specific conformational changes that control bond profiles, thereby suggesting structural mechanisms for the inner workings of the TCR mechanosensing machinery and plausible explanation of why and how force may amplify TCR signaling and antigen discrimination.

biophysics↗

bioRxiv2021

Cooperative binding of TCR and CD4 to pMHC enhances TCR sensitivity

Antigen recognition of CD4+ T cells by the T cell receptor (TCR) can be greatly enhanced by the coreceptor CD41-7. Yet, understanding of the molecular mechanism is hindered by the ultra-low affinity of CD4 binding to class-II peptide-major histocompatibility complexes (pMHC)1,7-10. Using two-dimensional (2D) mechanical-based assays, we determined a CD4-pMHC interaction to have 3-4 logs lower affinity than cognate TCR-pMHC interactions8, and to be susceptible to increased dissociation by forces (slip bond)5,8,11. In contrast, CD4 binds TCR-prebound pMHC at 3-6 logs higher affinity, forming TCR-pMHC-CD4 trimolecular bonds that are prolonged by force (catch bond)5,8,11 and modulated by protein mobility on the cell membrane, indicating profound TCR-CD4 cooperativity. Consistent with a tri-crystal structure12, using DNA origami as a molecular ruler to titrate spacing between TCR and CD4 indicates that 7-nm proximity optimizes trimolecular bond formation with pMHC. Our results reveal how CD4 augments TCR antigen recognition.

immunology↗

bioRxiv2018

Comparative transcriptome analysis reveals higher expression of stress and defense responsive genes in dwarf soybeans obtained from the crossing of G. max and G. soja

Plant height is an important component of plant architecture and significantly affects crop breeding practices and yield. We obtained a few segregated dwarf soybeans in the populations derived from the crossing of Glycine max var. Peking and Glycine soja var. IT182936 in an F5 RIL population. These dwarf soybeans may be useful genetic resources for plant breeders, geneticists and biologists. We attempted to find differentially expressed genes to classify and understand the regulation of genes related to plant growth in mutant dwarf soybeans, which appeared in the F5 generation. Using the Illumina high-throughput platform, transcriptomes were generated and compared among normal and dwarf soybeans in triplicate. We found complex relationship of the expressed genes to plant growth. There are highly significantly up-/downregulated genes according to the comparison of gene expression in normal and dwarf soybeans. The genes related to disease and stress responses were found to be upregulated in dwarf soybeans. Such over-expression of disease resistance and other immune response genes was targeted to understand how the immune genes regulate the response of plant growth. In addition, photosynthesis-related genes showed very low expression in dwarf lines. The transcriptome expression and genes classified as related to plant growth may be useful resources to researchers studying plant growth.

plant biology↗