Department of Chemistry, University of California, Berkeley, Berkeley, United States; California Institute for Quantitative Biosciences, University of California, Berkeley, Berkeley, United States; Howard Hughes Medical Institute, University of California, Berkeley, Berkeley, United States
Department of Chemistry, University of California, Berkeley, Berkeley, United States; California Institute for Quantitative Biosciences, University of California, Berkeley, Berkeley, United States; Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, United States
Anthony T Iavarone
California Institute for Quantitative Biosciences, University of California, Berkeley, Berkeley, United States; College of Chemistry Mass Spectrometry Facility, University of California, Berkeley, Berkeley, United States
Department of Chemistry, University of California, Berkeley, Berkeley, United States; California Institute for Quantitative Biosciences, University of California, Berkeley, Berkeley, United States; Institute for Digital Molecular Analytics and Science, Nanyang Technological University, Singapore, Singapore
Department of Chemistry, University of California, Berkeley, Berkeley, United States; California Institute for Quantitative Biosciences, University of California, Berkeley, Berkeley, United States; Howard Hughes Medical Institute, University of California, Berkeley, Berkeley, United States; Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, United States
The Tec-family kinase Btk contains a lipid-binding Pleckstrin homology and Tec homology (PH-TH) module connected by a proline-rich linker to a ‘Src module’, an SH3-SH2-kinase unit also found in Src-family kinases and Abl. We showed previously that Btk is activated by PH-TH dimerization, which is triggered on membranes by the phosphatidyl inositol phosphate PIP3, or in solution by inositol hexakisphosphate (IP6) (Wang et al., 2015, https://doi.org/10.7554/eLife.06074). We now report that the ubiquitous adaptor protein growth-factor-receptor-bound protein 2 (Grb2) binds to and substantially increases the activity of PIP3-bound Btk on membranes. Using reconstitution on supported-lipid bilayers, we find that Grb2 can be recruited to membrane-bound Btk through interaction with the proline-rich linker in Btk. This interaction requires intact Grb2, containing both SH3 domains and the SH2 domain, but does not require that the SH2 domain be able to bind phosphorylated tyrosine residues – thus Grb2 bound to Btk is free to interact with scaffold proteins via the SH2 domain. We show that the Grb2-Btk interaction recruits Btk to scaffold-mediated signaling clusters in reconstituted membranes. Our findings indicate that PIP3-mediated dimerization of Btk does not fully activate Btk, and that Btk adopts an autoinhibited state at the membrane that is released by Grb2.
