Disease relevance of SOS3

• SOS3 was cloned into a plasmid and expressed in Escherichia coli, allowing purification of the protein to homogeneity [1].
• In planta assays showed that the Thr(168)-to-Asp-activated mutant SOS2 partially rescued the salt hypersensitivity in sos2 and sos3 mutant plants [2].

High impact information on SOS3

• In Arabidopsis thaliana, the calcium binding protein Salt Overly Sensitive3 (SOS3) interacts with and activates the protein kinase SOS2, which in turn activates the plasma membrane Na(+)/H(+) antiporter SOS1 to bring about sodium ion homeostasis and salt tolerance [2].
• The SOS3 (for SALT OVERLY SENSITIVE3) calcium binding protein and SOS2 protein kinase are required for sodium and potassium ion homeostasis and salt tolerance in Arabidopsis [3].
• Constitutively active SOS2 that is SOS3 independent also was produced by changing Thr(168) to Asp in the activation loop of the SOS2 kinase domain [3].
• Gel mobility shift and (45)Ca(2)+ overlay assays demonstrated that SOS3 is a unique calcium binding protein and that the sos3-1 mutation substantially reduced the capacity of SOS3 to bind calcium [4].
• Expression of the myristoylated but not the nonmyristoylated SOS3 complemented the salt-hypersensitive phenotype of sos3-1 plants [4].

Biological context of SOS3

• The mutation is recessive and is in a nuclear gene that maps to chromosome V. The sos3 mutation also renders the plant unable to grow on low K+ [5].
• Also, mutations that alter the NaCl sensitivity of sos3-1 were screened for potential genetic suppressors or enhancers of salt-stress responses mediated by SOS3 [6].
• Targeted mutagenesis of the N-terminal glycine-2 to alanine prevented the myristoylation of SOS3 [4].
• SOS3 is an EF hand type calcium-binding protein having sequence similarities with animal neuronal calcium sensors and the yeast calcineurin B. SOS2 is a serine/threonine protein kinase in the SNF1/AMPK family [7].
• The SOS2/SOS3 kinase complex promoted the phosphorylation of SOS1 [8].

Anatomical context of SOS3

• In vitro translation assays with reticulocyte showed that the SOS3 protein was myristoylated [4].

Associations of SOS3 with chemical compounds

• The plant SOS2 protein kinase and its associated Ca(2+) sensor, SOS3, have been demonstrated to modulate the plasma membrane H(+)/Na(+) antiporter SOS1; however, how these regulators modulate Ca(2+) levels within cells is poorly understood [9].
• We report the crystal structure of a dimeric SOS3 protein in complex with calcium, and with calcium and manganese [10].
• SOS2 contains a sucrose-non-fermenting protein kinase 1/AMP-activated protein kinase-like N-terminal catalytic domain with an activation loop and a unique C-terminal regulatory domain with an FISL motif that binds to the calcium sensor Salt Overly Sensitive 3 [11].

Physical interactions of SOS3

• We report here the identification of a SOS3 binding motif in SOS2 that also serves as the kinase autoinhibitory domain [3].

Other interactions of SOS3

• Coexpression of SOS3 with SOS2 forms that retained the FISL motif resulted in more dramatic increases in salt tolerance [2].
• Based on these results, a genetic model for salt tolerance mechanisms in Arabidopsis is presented in which SOS1, SOS2, and SOS3 are postulated to encode regulatory components controlling plant K+ nutrition that in turn is essential for salt tolerance [12].
• CIPKs/PKS are a group of Ser/Thr protein kinases associated with the AtCBL/SOS3-like calcium-binding proteins (SCaBP) [13].
• In each of these yeast assays, the activation of CAX1 by SOS2 was SOS3-independent [9].

Analytical, diagnostic and therapeutic context of SOS3

• Yeast two-hybrid assays as well as in vitro binding assays revealed a 21-amino acid motif in the regulatory domain of SOS2 that is necessary and sufficient for interaction with SOS3 [3].
• Analytical ultracentrifugation experiments and circular dichroism measurements show that calcium binding is responsible for the dimerization of SOS3 [10].
• SOS3 (salt overly sensitive 3) from Arabidopsis thaliana: expression, purification, crystallization and preliminary X-ray analysis [1].

References