Mechanism of calcium/calmodulin inhibition of rod cyclic nucleotide-gated channels

doi:10.1073/pnas.122015999

Mechanism of calcium/calmodulin inhibition of rod cyclic nucleotide-gated channels

Department of Physiology and Biophysics, Howard Hughes Medical Institute, University of Washington Medical School, Box 357370, Seattle, WA 98195

Edited by Lily Y. Jan, University of California School of Medicine, San Francisco, CA, and approved April 16, 2002 (received for review January 9, 2002)

Abstract

Rod cyclic nucleotide-gated (CNG) channels are heterotetramers comprised of both CNGA1 and CNGB1 subunits. Calcium/calmodulin (Ca²⁺/CaM) binds to a site in the N-terminal region of CNGB1 subunits and inhibits the opening conformational change in CNGA1/CNGB1 channels. Here, we show that polypeptides derived from an N-terminal region of CNGB1 form a specific interaction with polypeptides derived from a C-terminal region of CNGA1 that is distal to the cyclic nucleotide-binding domain. Deletion of the Ca²⁺/CaM-binding site from the N-terminal region of CNGB1 eliminated both Ca²⁺/CaM modulation of the channel and the intersubunit interaction. Furthermore, the interaction was disrupted by the presence of Ca²⁺/CaM. These results suggest that Ca²⁺/CaM-dependent inhibition of rod channels is caused by the direct binding of Ca²⁺/CaM to a site in the N-terminal region in CNGB1, which disrupts the interaction between this region and a distal C-terminal region of CNGA1. The mechanism underlying Ca²⁺/CaM modulation of rod channels is distinct from that in olfactory (CNGA2) CNG channels.

Footnotes

↵ * To whom reprint requests should be addressed. E-mail: zagotta{at}u.washington.edu.
This paper was submitted directly (Track II) to the PNAS office.
Abbreviations:

CNG,

cyclic nucleotide-gated;

CaM,

calmodulin;

CNBD,

cyclic nucleotide-binding domain;

GST,

glutathione S-transferase