In:
The Journal of Neuroscience, Society for Neuroscience, Vol. 19, No. 20 ( 1999-10-15), p. 8830-8838
Abstract:
Small conductance Ca 2+ -activated potassium channels (SK channels) are coassembled complexes of pore-forming SK α subunits and calmodulin. We proposed a model for channel activation in which Ca 2+ binding to calmodulin induces conformational rearrangements in calmodulin and the α subunits that result in channel gating. We now report fluorescence measurements that indicate conformational changes in the α subunit after calmodulin binding and Ca 2+ binding to the α subunit–calmodulin complex. Two-hybrid experiments showed that the Ca 2+ -independent interaction of calmodulin with the α subunits requires only the C-terminal domain of calmodulin and is mediated by two noncontiguous subregions; the ability of the E-F hands to bind Ca 2+ is not required. Although SK α subunits lack a consensus calmodulin-binding motif, mutagenesis experiments identified two positively charged residues required for Ca 2+ -independent interactions with calmodulin. Electrophysiological recordings of SK2 channels in membrane patches from oocytes coexpressing mutant calmodulins revealed that channel gating is mediated by Ca 2+ binding to the first and second E-F hand motifs in the N-terminal domain of calmodulin. Taken together, the results support a calmodulin- and Ca 2+ -calmodulin-dependent conformational change in the channel α subunits, in which different domains of calmodulin are responsible for Ca 2+ -dependent and Ca 2+ -independent interactions. In addition, calmodulin is associated with each α subunit and must bind at least one Ca 2+ ion for channel gating. Based on these results, a state model for Ca 2+ gating was developed that simulates alterations in SK channel Ca 2+ sensitivity and cooperativity associated with mutations in CaM.
Type of Medium:
Online Resource
ISSN:
0270-6474
,
1529-2401
DOI:
10.1523/JNEUROSCI.19-20-08830.1999
Language:
English
Publisher:
Society for Neuroscience
Publication Date:
1999
detail.hit.zdb_id:
1475274-8
SSG:
12
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