Thu, 21 Aug 2008 15:34:28 BST CiteULike: lechristophe Theoharis http://www.citeulike.org/user/lechristophe/author/Theoharis CiteULike.org en-gb Copyright © 2004-2008 citeulike.org http://www.citeulike.org/user/lechristophe/article/2191080 <i>Biochemistry, Vol. 47, No. 1. (8 January 2008), pp. 112-123.</i><br /><br />Calmodulin (CaM) is the primary calcium sensor in eukaryotes. Calcium binds cooperatively to pairs of EF-hand motifs in each domain (N and C). This allows CaM to regulate cellular processes via calcium-dependent interactions with a variety of proteins, including ion channels. One neuronal target is NaV1.2, voltage-dependent sodium channel type II, to which CaM binds via an IQ motif within the NaV1.2 C-terminal tail (residues 1901-1938) [Mori, M., et al. (2000) Biochemistry 39, 1316-1323]. Here we report on the use of circular dichroism, fluorescein emission, and fluorescence anisotropy to study the interaction between CaM and NaV1.2 at varying calcium concentrations. At 1 mM MgCl2, both full-length CaM (CaM1-148) and a C-domain fragment (CaM76-148) exhibit tight (nanomolar) calcium-independent binding to the NaV1.2 IQ motif, whereas an N-domain fragment of CaM (CaM1-80) binds weakly, regardless of calcium concentration. Equilibrium calcium titrations of CaM at several concentrations of the NaV1.2 IQ peptide showed that the peptide reduced the calcium affinity of the CaM C-domain sites (III and IV) without affecting the N-domain sites (I and II) significantly. This leads us to propose that the CaM C-domain mediates constitutive binding to the NaV1.2 peptide, but that interaction then distorts calcium-binding sites III and IV, thereby reducing their affinity for calcium. This contrasts with the CaM-binding domains of voltage-dependent Ca2+ channels, kinases, and phosphatases, which increase the calcium binding affinity of the C-domain of CaM. The Neuronal Voltage-Dependent Sodium Channel Type II IQ Motif Lowers the Calcium Affinity of the C-Domain of Calmodulin. NT Theoharis BR Sorensen J Theisen-Toupal MA Shea doi:10.1021/bi7013129 Biochemistry, Vol. 47, No. 1. (8 January 2008), pp. 112-123. 2008-01-03T10:15:25-00:00 2008 Biochemistry 0006-2960 47 1 112 123 biochemistry calmodulin nav structure