SH3 Domain of C-Src Regulates its Dynamic Behavior in the Cell Membrane

Src family kinases are major non-receptor tyrosine kinase in cells and Src-mediated signal transduction involves various cellular functions. In activation process, Src molecules translocate to cell membrane and the subdomains in Src, SH2 and SH3 domains, are exposed. For Src to serve as a kinase, the interaction with its substrates via SH2 and/or SH3 domains is required. Although the activation mechanism of Src has been well-studied, the dynamics of Src at the cell membrane is still unclear. In this study, we examined the role of Src subdomains, especially SH2 and SH3 domains, on the dynamics of Src at the cell membrane. To achieve this, we constructed PAmCherry-tagged wild-type Src (SrcWT), SrcW121A and SrcR178A mutants that decrease the binding of Src to its substrate(s) via SH3 and SH2 domains, respectively, and traced individual Src molecules in the cell membrane with gentle activation of PAmCherry. SrcWT dynamically moved on the cell membrane in the range of 0.27±0.01 μm2/s within a few seconds. The dynamics of SrcR178A mutant was comparable with that of SrcWT, whereas SrcW121A mutant exhibited less mobility (0.16±0.01 μm2/s) at the cell membrane compared with SrcWT. Since both SrcW121A and SrcR178A mutants showed higher phosphorylation level than SrcWT, the result indicates that the less mobility of SrcW121A in the cell membrane seems not to depend upon Src activation status. We further demonstrate that SrcW121A mutant showed ∼30% increase in the Src molecules residence time at focal adhesion compared with SrcWT, which is mediated by slower dissociation from adhesion site. Taken together with enhanced localization of SrcW121A at focal adhesion, our findings show that the SH3 domain of Src molecules governs dynamics of Src at the cell membrane, which may be involved in the rapid signal transduction in cells.