Detecting protein kinase recognition modes of calmodulin by residual dipolar couplings in solution NMR

Calmodulin-regulated serine/threonine kinases (CaM kinases) play crucial roles in Ca²⁺-dependent signaling transduction pathways in eukaryotes. Despite having a similar overall molecular architecture of catalytic and regulatory domains, CaM kinases employ different binding modes for Ca²⁺/CaM recruitment which is required for their activation. Here we present a residual dipolar coupling (RDC)-based NMR approach to characterizing the molecular recognition of CaM with five different CaM kinases. Our analyses indicate that CaM kinase I and likely IV use the same CaM binding mode as myosin light chain kinase (1-14 motif), distinct from those of CaM kinase II (1-10 motif) and CaM kinase kinase (1-16^- motif). This NMR approach provides an efficient experimental guide for homology modeling and structural characterization of CaM - target complexes.