An IQ Domain Mediates the Interaction with Calmodulin in a Plant Cyclic Nucleotide-Gated Channel.

Cyclic nucleotide-gated channels (CNGCs) form non-selective cation entry pathways regulated by calmodulin (CaM), a universal Ca(2+) sensor in eukaryotes. Although CaM-binding has been shown to be important for Ca(2+)-dependent feedback regulation of CNG channel activity, the CaM-binding properties of these channels have been investigated in a few cases only.We show ...
that CNGC20 from Arabidopsis thaliana binds CaM in a Ca(2+)-dependent manner and interacts with all AtCaM isoforms but not with the CaM-like proteins CML8 and CML9. CaM interaction with the full-length channel was demonstrated in planta, using bimolecular fluorescence complementation. This interaction occurred at the plasma membrane, in accordance with our localisation data of GFP-fused CNGC20 proteins. The CaM binding site was mapped to an isoleucine glutamine (IQ) motif, which has not been characterised in plant CNG channels so far.Our results show that compared to the overlapping binding sites for cyclic nucleotides and CaM in CNG channels studied so far, they are sequentially organised in CNGC20. The presence of two alternative CaM binding modes indicates that ligand regulation of plant CNGCs is more complex than previously expected. Since the IQ domain is conserved among plant CNGCs, this domain adds to the variability of Ca(2+)-dependent channel control mechanisms underlining the functional diversity within this multigene family.
Plant Cell Physiol.
Date: Feb. 05, 2013
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