SOLUTION STRUCTURE OF CALMODULIN-W-7 COMPLEX - THE BASIS OF DIVERSITYIN MOLECULAR RECOGNITION

The solution structure of calcium-bound calmodulin (CaM) complexed wit h an antagonist, N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide (W -7), has been determined by multidimensional NMR spectroscopy. The str ucture consists of one molecule of W-7 binding to each of the two doma ins of CaM. In each domain, the W-7 chloronaphthalene ring interacts w ith four methionine methyl groups and other aliphatic or aromatic side -chains in a deep hydrophobic pocket, the site responsible for CaM bin ding to CaM-dependent enzymes such as myosin Light chain kinases (MLCK s) and CaM kinase II. This competitive binding at the same site betwee n W-7 and CaM-dependent enzymes suggests the mechanism by which W-7 in hibits CaM to activate the enzymes. The orientation of the W-7 naphtha lene ring in the N-terminal pocket is rotated approximately 40 degrees with respect to that in the C-terminal pocket. The W-7 ring orientati on differs significantly from the Trp800 indole ring of smooth muscle MLCK bound to the C-terminal pocket and the phenothiazine ring of trif luoperazine bound to the N or C-terminal pocket. These comparative str uctural analyses demonstrate that the two hydrophobic pockets of CaM c an accommodate a variety of bulky aromatic rings, which provides a pla usible structural basis for the diversity in CaM-mediated molecular re cognition. (C) 1998 Academic Press Limited.