Structural and Molecular Dynamic Simulation Studies of CBL-Interacting Protein Kinase CIPK and its Complexes Related to Plant Salinity Stress

Abstract

Abstract Calcium-dependent signaling in plants is responsible for several major cellular events, including the activation of the salinity-responsive pathways. Calcium binds to calcineurin B-like protein (CBL), and the CBL-Ca2+ binds to CBL-interacting protein kinase (CIPK). The CBL-CIPK complex enhances the CIPK interaction with an upstream kinase. The upstream kinase phosphorylates CIPK that, in turn, phosphorylates membrane transporters. Targeted membrane transporter phosphorylation influences its activity and kick-starts many downstream functions, such as balancing the cytosolic Na+-to-K+ ratio. The CBL-CIPK interaction is pivotal for Ca2+-dependent salinity stress signaling. The plant contains multiple CBL and CIPK genes coded in their genomes. Hence, different yet specific combinations of CBL and CIPK are responsible for targeting particular ion transporters. Here, we present the computationally predicted structures of autoinhibited CIPK24 and CIPK24-CBL4 complex. The models are supported by the available structural and functional data. Models are energy-minimized and subjected to molecular dynamics (MD) simulations. MD simulations enabled us to predict the importance of conserved residues of the proteins. Finally, the work is extended to predict the CIPK24-CBL4 complex with the upstream kinase GIRK2. MD simulation on the ternary complex structure enabled us to identify the critical CIPK24-GIRK2 interactions. Together, these data could be used to engineer the CBL-CIPK interaction network for developing salt tolerance in crops.