Activation of the plasma membrane Na/H antiporter Salt-Overly-Sensitive 1 (SOS1) by phosphorylation of an auto-inhibitory C-terminal domain

Quintero et al.-- 6 páginas, 4 figuras, 25 referencias y 4 páginas adicionales con 5 figuras y 2 tablas.
The plasma membrane sodium/proton exchanger Salt-Overly-Sensitive 1 (SOS1) is a critical salt tolerance determinant in plants. The SOS2-SOS3 calcium-dependent protein kinase complex up-regulates SOS1 activity, but the mechanistic details of this crucial event remain unresolved. Here we show that SOS1 is maintained in a resting state by a C-terminal auto-inhibitory domain that is the target of SOS2-SOS3. The auto-inhibitory domain interacts intramolecularly with an adjacent domain of SOS1 that is essential for activity. SOS1 is relieved from auto-inhibition upon phosphorylation of the auto-inhibitory domain by SOS2-SOS3. Mutation of the SOS2 phosphorylation and recognition site impeded the activation of SOS1 in vivo and in vitro. Additional amino acid residues critically important for SOS1 activity and regulation were identified in a genetic screen for hypermorphic alleles.
This work was supported by Grants BIO2009-08641 and CSD2007-00057 from the Ministerio de Ciencia e Innovación (cofinanced by Fondo Europeo de Desarrollo Regional) (to J.M.P. and F.J.Q.), World Class University Program Grant R32-10148 (to D.-J.Y. and W.Y.K.), and National Institutes of Health Grants R01GM070795 and R01GM059138 (to J.-K.Z.).