THE LINKER OF DES-GLU(84)-CALMODULIN IS BENT

The crystal structure of a mutant calmodulin (CaM) lacking Glu-84 has been refined to R = 0.23 using data measured to 2.9-angstrom resolutio n. In native CaM the central helix is fully extended, and the molecule is dumbbell shaped. In contrast, the deletion of Glu-84 causes a bend of 95-degrees in the linker region of the central helix at Ile-85. Ho wever, EF-hand domains 1 and 2 (lobe 1,2) do not touch lobe 3,4. The l ength, by alpha-carbon separation, of des-Glu84-CaM is 56 angstrom; th at of native CaM is 64 angstrom. The shape of des-Glu84-CaM is similar to that of native CaM, as it is bound to the target peptide of myosin light-chain kinase. This result supports the proposal that the linker region of the central helix of CaM functions as a flexible tether.