SINGLE CYCLIC NUCLEOTIDE-GATED CHANNELS LOCKED IN DIFFERENT LIGAND-BOUND STATES

Authors
Citation
M. Ruiz et Jw. Karpen, SINGLE CYCLIC NUCLEOTIDE-GATED CHANNELS LOCKED IN DIFFERENT LIGAND-BOUND STATES, Nature, 389(6649), 1997, pp. 389-392
Citations number
27
Categorie Soggetti
Multidisciplinary Sciences
Journal title
NatureACNP
ISSN journal
00280836
Volume
389
Issue
6649
Year of publication
1997
Pages
389 - 392
Database
ISI
SICI code
0028-0836(1997)389:6649<389:SCNCLI>2.0.ZU;2-3
Abstract
Cyclic nucleotide-gated (CNG) channels are directly activated by the b inding of several ligands(1-6). For these channels as well as for othe r allosteric proteins, the functional effects of each ligand-binding e vent have been difficult to assess because ligands continuously bind a nd unbind at each site. Furthermore, in retinal rod photoreceptors the low cytoplasmic concentration of cyclic GMP(7) means that channels ex ist primarily in partially liganded states, so it is important to dete rmine how such channels behave. Previous studies of single channels ha ve suggested that they occasionally open to subconducting states at lo w cGMP(2,3,8-10), but the significance of these states and how they ar ise is poorly understood. Here we combine the high resolution of singl e-channel recording with the use of a photoaffinity analogue of cGMP(1 1,12) that tethers cGMP moieties covalently to their binding sites to show single retinal CNG channels can be effectively locked in four dis tinct ligand-bound states. Our results indicate that channels open mor e than they would spontaneously when two ligands are bound (similar to 1% of the maximum current), significantly more with three ligands bou nd (similar to 33%), and open maximally with four ligands bound. In ea ch ligand-bound state, channels opened to two or three different condu ctance states, These findings place strong constraints on the activati on mechanism of CNG channels.