Mapping the BK sub(Ca) Channel's "Ca super(2+) Bowl": Side-chains Essential for Ca super(2+) Sensing

• Published in: The Journal of general physiology 2004-05, Vol.123 (5), p.475-489
• Main Authors: Bao, Lin, Kaldany, C, Holmstrand, E C, Cox, D H
• Format: Article
• Language: English
• ISSN: 0022-1295
• DOI: 10.1085/jgp.200409052

There is controversy over whether Ca super(2+) binds to the BK sub(Ca) channel's intracellular domain or its integral-membrane domain and over whether or not mutations that reduce the channel's Ca super(2+) sensitivity act at the point of Ca super(2+) coordination. One region in the intracellular domain that has been implicated in Ca super(2+) sensing is the "Ca super(2+) bowl". This region contains many acidic residues, and large Ca super(2+)-bowl mutations eliminate Ca super(2+) sensing through what appears to be one type of high-affinity Ca super(2+)-binding site. Here, through site-directed mutagenesis we have mapped the residues in the Ca super(2+) bowl that are most important for Ca super(2+) sensing. We find acidic residues, D898 and D900, to be essential, and we find them essential as well for Ca super(2+) binding to a fusion protein that contains a portion of the BK sub(Ca) channel's intracellular domain. Thus, much of our data supports the conclusion that Ca super(2+) binds to the BK sub(Ca) channel's intracellular domain, and they define the Ca super(2+) bowl's essential Ca super(2+)-sensing motif. Overall, however, we have found that the relationship between mutations that disrupt Ca super(2+) sensing and those that disrupt Ca super(2+) binding is not as strong as we had expected, a result that raises the possibility that, when examined by gel-overlay, the Ca super(2+) bowl may be in a nonnative conformation.