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. 1998 Apr 15;17(8):2273–2284. doi: 10.1093/emboj/17.8.2273

Calmodulin controls the rod photoreceptor CNG channel through an unconventional binding site in the N-terminus of the beta-subunit.

D Weitz 1, M Zoche 1, F Müller 1, M Beyermann 1, H G Körschen 1, U B Kaupp 1, K W Koch 1
PMCID: PMC1170571  PMID: 9545240

Abstract

Calmodulin (CaM) controls the activity of the rod cGMP-gated ion channel by decreasing the apparent cGMP affinity. We have examined the mechanism of this modulation using electrophysiological and biochemical techniques. Heteromeric channels, consisting of alpha- and beta-subunits, display a high CaM sensitivity (EC50 </=5 nM) similar to the native channel. Using surface plasmon resonance spectroscopy, we identified two unconventional CaM-binding sites (CaM1 and CaM2), one in each of the N- and the C-terminal regions of the beta-subunit. Ca2+ co-operatively stimulates binding of CaM to these sites exactly within the range of [Ca2+] occurring during a light response. Deletion of the N-terminal CaM1 site results in channels that are no longer CaM-sensitive, whereas deletion of CaM2 has only minor effects. We discuss different models to explain the high-affinity binding of CaM.

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Selected References

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