title: Calmodulin overexpression does not alter Cav1.2 function or oligomerization state.
abstract: Interactions between calmodulin (CaM) and voltage-gated calcium channels (Ca(v)s) are crucial for Ca(v) activity-dependent feedback modulation. We recently reported an X-ray structure that shows two Ca(2+)/CaM molecules bound to the Ca(v)1.2 C terminal tail, one at the PreIQ region and one at the IQ domain. Surprisingly, the asymmetric unit of the crystal showed a dimer in which Ca(2+)/CaM bridged two PreIQ helixes to form a 4:2 Ca(2+)/CaM:Ca(v) C-terminal tail assembly. Contrary to previous proposals based on a similar crystallographic dimer, extensive biochemical analysis together with subunit counting experiments of full-length channels in live cell membranes failed to find evidence for multimers that would be compatible with the 4:2 crossbridged complex. Here, we examine this possibility further. We find that CaM over-expression has no functional effect on Ca(v)1.2 inactivation or on the stoichiometry of full-length Ca(v)1.2. These data provide further support for the monomeric Ca(v)1.2 stoichiometry. Analysis of the electrostatic surfaces of the 2:1 Ca(2+)/CaM:Ca(V) C-terminal tail assembly reveals notable patches of electronegativity. These could influence various forms of channel modulation by interacting with positively charged elements from other intracellular channel domains.
authors.affiliation: Cardiovascular Research Institute, University of California, San Francisco, USA.
authors.forename: Felix
authors.initials: F
authors.lastname: Findeisen
authors.forename: Alexandra
authors.initials: A
authors.lastname: Tolia
authors.forename: Ryan
authors.initials: R
authors.lastname: Arant
authors.forename: Eun Young
authors.initials: EY
authors.lastname: Kim
authors.forename: Ehud
authors.initials: E
authors.lastname: Isacoff
authors.forename: Daniel L
authors.initials: DL
authors.lastname: Minor
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D020746:Calcium Channels, L-Type / Q000235:genetics / Q000378:metabolism*; D002147:Calmodulin / Q000096:biosynthesis* / Q000235:genetics; D002462:Cell Membrane / Q000235:genetics / Q000378:metabolism*; D015870:Gene Expression; D006801:Humans; D055503:Protein Multimerization; D017434:Protein Structure, Tertiary; D014982:Xenopus laevis
chemical_list: C079146:CACNA1C protein, human; D020746:Calcium Channels, L-Type; D002147:Calmodulin; D002118:Calcium