Target-induced conformational adaptation of calmodulin revealed by the crystal structure of a complex with nematode Ca2+/calmodulin-dependent kinase kinase peptide

Calmodulin (CaM) is a ubiquitous calcium (Ca2+) sensor which binds and regu lates protein serine/threonine kinases along with many other proteins in a Ca2+-dependent manner. For thus multi-functionality, conformational plastic ity is essential; however, the nature and magnitude of CaM's plasticity sti ll remains largely undetermined. Here, we present the 1.8 Angstrom resoluti on crystal structure of Ca2+/CaM, complexed with the 27-residue synthetic p eptide corresponding to the CaM-binding domain of the nematode Caenorhabdit is elegans Ca2+/CaM-dependent kinase kinase (CaMKK). The peptide bound in t his crystal structure is a homologue of the previously NMR-derived complex with rat CaMKK, but benefits from improved structural resolution. Careful c omparison of the present structure to previous crystal structures of CaM co mplexed with unrelated peptides derived from myosin light chain kinase and CaM kinase II, allow a quantitative analysis of the differences in the rela tive orientation of the N and C-terminal domains of CaM, defined as a screw axis rotation angle ranging from 156 degrees to 196 degrees. The principal differences in CaM interaction with various peptides are associated with t he N-terminal domain of CaM. Unlike the C-terminal domain, which remains un changed internally, the N-terminal domain of CaM displays significant diffe rences in the EF-hand helix orientation between this and other CaM structur es. Three hydrogen bonds between CaM and the peptide (E87-R336, E87-T339 an d K75-T339) along with two salt bridges (E11-R349 and E114-K334) are the mo st probable determinants for the binding direction of the CaMKK peptide to CaM. (C) 2001 Academic Press.