Single-molecule behavior and cell-growth regulation in human RTKs

Receptor tyrosine kinases (RTKs) are a major family of cell surface receptor proteins responsible for various cellular functions in animal cells, including fate decisions, metabolism, polarization and migration. Lateral mobility, dimerization, clustering, and oligomerization are crucial behaviors in the activation process of RTKs on the cell surface. However, relationships between these molecular behaviors and molecular function remain to be elucidated, except for a few RTK members. Here, using an automated live-cell single-molecule imaging and analysis system, we studied the behavior of 52 of the 58 human RTK species on living cells over time during stimulation with ligands. We extracted 72 single-molecule parameters for each RTK species to examine their relationship to function, structure, and evolution. We noticed that RTKs’ ability to inhibit or support cell growth, as observed in a large-scale loss-of-function experiment in the public domain, significantly relates to their behavior. Growth-inhibitory signaling was coupled with the immediate formation of immobile clusters, followed by the enlargement of immobile and slow-mobile domains. In contrast, growth-supportive signaling coupled with higher lateral diffusivity and delayed clustering of immobile molecules. The relationship between structure and function suggests that functional differences are related to partitioning into membrane rafts and changes in mobility associated with phosphatidylinositol turnover. In multiple linear regression models, molecular behavior explained half or more of the molecular function related to cell growth. This level of explainability is comparable to that of evolutionary grouping.