Plant plasma membrane 14-3-3 proteins differ in solubility and form fusicoccin-dependent complexes

The binding protein for the phytotoxin fusicoccin belongs to the class of highly conserved 14-3-3 proteins. A general principle for the mode of action of 14-3-3 proteins is that they serve as docking clamps in order to facilitate protein interactions. This implies that 14-3-3 proteins may behave according to the proteins they interact with. Plasma membrane (PM) 14-3-3 proteins from oat roots indeed exhibited different properties, for example with respect to detergent solubility. The most abundant 14-3-3's with apparent molecular masses of 30 and 31 kDa, could be largely solubilized from the plasma membrane in high detergent buffer. However, part of these solubilized 14-3-3's precipitated when the detergent concentration was reduced. Moreover, a minor 35 kDa 14-3-3 protein was soluble in high detergent buffer but also completely precipitated at low detergent buffer. We present evidence that this 35 kDa 14-3-3 protein is phosphorylated and that the lower mobility in SDS-PAGE is likely to be due to binding of Ca