The authors consider small and poorly-studied groups of plant calcium-dependent protein kinases that directly interact with calmodulin molecules. In plants, Ca2+ activates calmodulin-like domain kinases that do not require calmodulin or phospholipids. Thus these kinases differ from both CaMK and PKC families prevalent in mammalian cells.Next, various strategies of purification of recombinant proteins using CaM-based purification systems are reviewed and discussed. Protein purification is a crucial process in biotechnology industries and life science research laboratories. Amongst these purification strategies, affinity purification has garnered a lot of attention due to its higher speed and selectivity, leading to enhanced purity in fewer steps.In the closing chapter, the authors describe atomic-level structures of Ca2+-bound CaM (Ca2+/CaM) bound to the PSD-95 N-terminal domain. The N-lobe of CaM forms a cap that binds to the N-terminus of PSD-95 and sterically blocks the palmitoylation of PSD-95 at Cys3 and Cys5. The CaM C-lobe forms hydrophobic contacts with PSD-95 residue Y12, and the Y12E mutation abolishes Ca2+-induced postsynaptic release of PSD-95.