Chemical shift assignments of calmodulin bound to the β-subunit of a retinal cyclic nucleotide-gated channel (CNGB1)

Aritra Bej,James B Ames

doi:10.1007/s12104-022-10072-9

Abstract

Rod cyclic nucleotide-gated (CNG) channels are formed by two protein subunits (CNGA1 and CNGB1). Calmodulin (CaM) binds to the cytosolic regulatory domain of CNGB1 and decreases the open probability of CNGA1/CNGB1 channels. The CaM binding site within bovine CNGB1 (residues 679–702) binds tightly to Ca2+-bound CaM, which promotes Ca2+-induced inactivation of CNGA1/CNGB1 channels in retinal rods. We report complete NMR chemical shift assignments of Ca2+-saturated CaM bound to the CaM-binding domain of CNGB1 (BMRB no. 51222).

Highlights

Cyclic nucleotide-gated (CNG) channels expressed in retinal rods conduct a cation current in response to changes in intracellular levels of cGMP that occur during visual phototransduction (Baylor 1996, Fesenko, Kolesnikov et al 1985). Ca2+-dependent regulation of photoreceptor cyclic nucleotide-gated (CNG) channels by CaM is important for promoting light adaptation in photoreceptor cells (Bradley et al 2005, Fain et al 2001, Hsu and Molday 1993)
Native CNG channels in retinal rods form a heteromeric tetramer comprised of a 3:1 stoichiometry of CNGA1:CNGB1 (Shuart, Haitin et al, 2011)
Structures are known for CaM bound to the CNGA2 subunit from olfactory CNG channels (Contessa et al 2005), atomic level structural information is currently not known for CaM bound to the retinal CNGB1

Summary

Biological context

Cyclic nucleotide-gated (CNG) channels expressed in retinal rods conduct a cation current in response to changes in intracellular levels of cGMP that occur during visual phototransduction (Baylor 1996, Fesenko, Kolesnikov et al 1985). Ca2+-dependent regulation of photoreceptor CNG channels by CaM is important for promoting light adaptation in photoreceptor cells (Bradley et al 2005, Fain et al 2001, Hsu and Molday 1993). Ca2+-dependent regulation of photoreceptor CNG channels by CaM is important for promoting light adaptation in photoreceptor cells (Bradley et al 2005, Fain et al 2001, Hsu and Molday 1993). The Ca2+ sensor protein, calmodulin (CaM) binds to a cytosolic site in CNGB1 (residues 679-702) (Trudeau and Zagotta 2002) that may regulate CNGB1 binding to CNGA1 (Shuart et al 2011) and perhaps mediate C a2+-induced CNG channel inactivation in rod cells We report here NMR resonance assignments of Ca2+-saturated CaM bound to the CaM-binding domain of CNGB1 (hereafter called CaM/CNGB1) These assignments are a first step toward elucidating the structure of CaM bound to CNGB1

Expression and purification of CaM

NMR spectroscopy

Findings

Extent of assignments and data deposition