Calmodulin overexpression does not alter Cav1.2 function or oligomerization state

Channels (Austin). 2011 Jul-Aug;5(4):320-4. doi: 10.4161/chan.5.4.16821. Epub 2011 Jul 1.

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.

MeSH terms

  • Animals
  • Calcium / metabolism*
  • Calcium Channels, L-Type / genetics
  • Calcium Channels, L-Type / metabolism*
  • Calmodulin / biosynthesis*
  • Calmodulin / genetics
  • Cell Membrane / genetics
  • Cell Membrane / metabolism*
  • Gene Expression*
  • Humans
  • Protein Multimerization*
  • Protein Structure, Tertiary
  • Xenopus laevis

Substances

  • CACNA1C protein, human
  • Calcium Channels, L-Type
  • Calmodulin
  • Calcium