Journal
JOURNAL OF GENERAL PHYSIOLOGY
Volume 123, Issue 5, Pages 475-489Publisher
ROCKEFELLER UNIV PRESS
DOI: 10.1085/jgp.200409052
Keywords
mSlo; BKCa; potassium channel; Ca2+ bowl; Ca2+ binding
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Funding
- NHLBI NIH HHS [R01 HL064831, R01HL64831] Funding Source: Medline
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There is controversy over whether Ca2+ binds to the BKca channel's intracellular domain or its integral-membrane domain and over whether or not mutations that reduce the channel's Ca2+ sensitivity act at the point of Ca2+ coordination. One region in the intracellular domain that has been implicated in Ca2+ sensing is the Ca2+ bowl. This region contains many acidic residues, and large Ca2+-bowl mutations eliminate Ca2+ sensing through what appears to be one type of high-affinity Ca2+-binding site. Here, through site-directed mutagenesis we have mapped the residues in the Ca2+ bowl that are most important for Ca2+ Sensing. We find acidic residues, D898 and D900, to be essential, and we find them essential as well for Ca2+ binding to a fusion protein that contains a portion of the BKca channel's intracellular domain. Thus, much of our data supports the conclusion that Ca2+ binds to the BKca channel's intracellular domain, and they define the Ca2+ bowl's essential Ca2+-sensing motif. Overall, however, we have found that the relationship between mutations that disrupt Ca2+ sensing and those that disrupt Ca2+ binding is not as strong as we had expected, a result that: raises the possibility that, when examined by gel-overlay, the Ca2+ bowl may be in a nonnative conformation.
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