Mechanical modulation of receptor-ligand interactions at cell-cell interfaces

Cell surface receptors are known to regulate signal transduction pathways that influence cellular functions. While much is understood about how these receptors operate, their behavior at cell-cell interfaces remains unclear. Specifically, immune receptors like T-cell antigen receptors interact with ligands anchored to other cells, yet the process of receptor phosphorylation, termed receptor triggering, is not fully understood. Recent studies have shown that receptor-ligand complex lifetimes at cell-cell interfaces are shorter than those observed in solution. This discrepancy suggests a mechanistic difference at the interface. At the interface, receptor-ligand complexes span a short intermembrane distance, while longer surface molecules, including phosphatases like CD45, span greater distances. A proposed mechanism involves the segregation of these longer molecules from the receptor-ligand complex. However, the mechanochemical basis for this segregation remains unverified. This uncertainty has driven the need for a detailed model to explore the physical forces involved in receptor triggering.

This study aimed to investigate the physical mechanisms underlying receptor triggering at cell-cell interfaces. The specific problem addressed is the lack of understanding about how receptor-ligand complex lifetimes are affected by the intermembrane distance and the presence of longer surface molecules. The motivation stems from the observation that receptor-ligand complexes at interfaces have shorter lifetimes than in solution. The study sought to determine whether mechanochemical forces could explain the segregation of longer surface molecules from receptor-ligand complexes. By developing a mathematical model, the researchers aimed to simulate the interactions between membranes and surface molecules. The goal was to test the hypothesis that size-based segregation of longer surface molecules could influence receptor triggering. The model would also help predict how tension affects the lifetime of receptor-ligand complexes at interfaces.

The researchers developed a mathematical model that combined membrane elasticity with the compressional stiffness and lateral mobility of longer surface molecules. The model simulated the behavior of receptor-ligand complexes at cell-cell interfaces. The model accounted for the physical properties of membranes and the mechanical forces acting on surface molecules. It incorporated parameters such as intermembrane distance and the mobility of surface molecules. The researchers analyzed the segregation of longer surface molecules from receptor-ligand complexes using the model. They focused on how size differences between molecules affect their distribution at the interface. The model predicted the redistribution of longer surface molecules over time. The researchers also examined how this redistribution influences the tension on the receptor-ligand complex and its lifetime.

The model predicted robust supradiffusive segregation of longer surface molecules from receptor-ligand complexes at cell-cell interfaces. This segregation occurred despite the small intermembrane distance of 15 nm. The model showed that the redistribution of longer surface molecules leads to time-dependent tension on the receptor-ligand complex. This tension results in a decreased two-dimensional lifetime of the complex at the interface. The model also predicted a nonlinear relationship between the three- and two-dimensional lifetimes of the complex. This relationship could enhance the receptor's ability to distinguish between similar ligands. The findings suggest that mechanochemical forces play a role in receptor triggering. The model provides a framework for understanding how physical forces influence receptor-ligand interactions at interfaces.

The model supports the idea that mechanochemical forces contribute to receptor triggering at cell-cell interfaces. The segregation of longer surface molecules from receptor-ligand complexes is a predicted outcome of the model. The redistribution of these molecules leads to tension on the complex, which affects its lifetime. The nonlinear relationship between three- and two-dimensional lifetimes suggests a mechanism for ligand discrimination by receptors. The findings align with the hypothesis that size-based segregation of surface molecules influences receptor triggering. The model provides a framework for understanding the physical forces involved in receptor-ligand interactions. The results suggest that tension generated by membrane elasticity affects the stability of receptor-ligand complexes. These conclusions are based on the predictions of the mathematical model and the observed behavior of surface molecules at interfaces.