Data from: Conditional requirement for dimerization of the membrane-binding module for BTK signaling in lymphocyte cell lines

Bruton’s tyrosine kinase (BTK) is a major drug target in immune cells. The
membrane-binding pleckstrin homology and tec homology (PH-TH) domains of
BTK are required for signaling. Dimerization of the PH-TH module strongly
stimulates the kinase activity of BTK in vitro. Here, we investigated
whether BTK dimerizes in cells using the PH-TH module and whether this
dimerization is necessary for signaling. To address this question, we
developed high-throughput mutagenesis assays for BTK function in Ramos B
cells and Jurkat T cells. We measured the fitness costs for thousands of
point mutations in the PH-TH module and kinase domain to assess whether
dimerization of the PH-TH module and BTK kinase activity were necessary
for function. In Ramos cells, we found that neither PH-TH dimerization nor
kinase activity was required for BTK signaling. Instead, in Ramos cells,
BTK signaling was enhanced by PH-TH module mutations that increased
membrane adsorption, even at the cost of reduced PH-TH dimerization. In
contrast, in Jurkat cells, we found that BTK signaling depended on both
PH-TH dimerization and kinase activity. Evolutionary analysis indicated
that BTK proteins in organisms that evolved before the divergence of
ray-finned fishes lacked PH-TH dimerization but had active kinase domains,
similar to other Tec family kinases. Thus, PH-TH dimerization is a
distinct feature of BTK that evolved to exert stricter regulatory control
on kinase activity as adaptive immune systems gained increased complexity.