Interaction specificity of Arabidopsis calcineurin B-like calcium sensors and their target kinases

Calcium is a critical component in a number of plant signal transduction pa thways. A new family of calcium sensors called calcineurin B-like proteins (AtCBLs) have been recently identified from Arabidopsis. These calcium sens ors have been shown to interact with a family of protein kinases (CIPKs). H ere we report that each individual member of AtCBL family specifically inte racts with a subset of CIPKs and present structural basis for the interacti on and for the specificity underlying these interactions. Although the C-te rminal region of CIPKs is responsible for interaction with AtCBLs, the N-te rminal region of CIPKs is also involved in determining the specificity of s uch interaction. We have also shown that all three EF-hand motifs in AtCBL members are required for the interaction with CIPKs. Several AtCBL members failed to interact with any of the CIPKs presented in this study, suggestin g that these AtCBL members either have other CIPKs as targets or they targe t distinct proteins other than CIPKs. These results may provide structural basis for the functional specificity of CBL family of calcium sensors and t heir targets.