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Calmodulin controls the rod photoreceptor CNG channel through an unconventional binding site in the N‐terminus of the β‐subunit
Author(s) -
Weitz Dietmar,
Zoche Martin,
Müller Frank,
Beyermann Michael,
Körschen Heinz G.,
Kaupp U. Benjamin,
Koch KarlWilhelm
Publication year - 1998
Publication title -
the embo journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 7.484
H-Index - 392
eISSN - 1460-2075
pISSN - 0261-4189
DOI - 10.1093/emboj/17.8.2273
Subject(s) - physics , humanities , philosophy
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 α‐ and β‐subunits, display a high CaM sensitivity (EC 50 ⩽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 β‐subunit. Ca 2+ co‐operatively stimulates binding of CaM to these sites exactly within the range of [Ca 2+ ] 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.