title: Thermodynamic linkage between calmodulin domains binding calcium and contiguous sites in the C-terminal tail of Ca(V)1.2.
abstract: Calmodulin (CaM) binding to the intracellular C-terminal tail (CTT) of the cardiac L-type Ca(2+) channel (Ca(V)1.2) regulates Ca(2+) entry by recognizing sites that contribute to negative feedback mechanisms for channel closing. CaM associates with Ca(V)1.2 under low resting [Ca(2+)], but is poised to change conformation and position when intracellular [Ca(2+)] rises. CaM binding Ca(2+), and the domains of CaM binding the CTT are linked thermodynamic functions. To better understand regulation, we determined the energetics of CaM domains binding to peptides representing pre-IQ sites A(1588), and C(1614) and the IQ motif studied as overlapping peptides IQ(1644) and IQ'(1650) as well as their effect on calcium binding. (Ca(2+))(4)-CaM bound to all four peptides very favorably (K(d)≤2 nM). Linkage analysis showed that IQ(1644-1670) bound with a K(d)~1 pM. In the pre-IQ region, (Ca(2+))(2)-N-domain bound preferentially to A(1588), while (Ca(2+))(2)-C-domain preferred C(1614). When bound to C(1614), calcium binding in the N-domain affected the tertiary conformation of the C-domain. Based on the thermodynamics, we propose a structural mechanism for calcium-dependent conformational change in which the linker between CTT sites A and C buckles to form an A-C hairpin that is bridged by calcium-saturated CaM.
authors.affiliation: Department of Biochemistry, Roy J. and Lucille A. Carver College of Medicine, University of Iowa, Iowa City, IA 52242-1109, United States. idil-apak@uiowa.edu
authors.forename: T Idil Apak
authors.initials: TI
authors.lastname: Evans
authors.forename: Johannes W
authors.initials: JW
authors.lastname: Hell
authors.forename: Madeline A
authors.initials: MA
authors.lastname: Shea
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D020746:Calcium Channels, L-Type / Q000737:chemistry / Q000378:metabolism*; D002147:Calmodulin / Q000737:chemistry / Q000378:metabolism*; D020134:Catalytic Domain; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011485:Protein Binding; D051381:Rats; D013816:Thermodynamics
chemical_list: D020746:Calcium Channels, L-Type; D002147:Calmodulin; C419385:L-type calcium channel alpha(1C); D002118:Calcium