Abstract
The molecular basis of a severe developmental and neurological disorder associated with a de novo G375R variant of the tetrameric BK channel is unknown. Here we address this question by recording from single BK channels expressed for a heterozygous G375R mutation. Five different types of functional BK channels were observed: 3% were WT, 12% were homomeric mutant, and 85% were three different types of hybrid channels. All channel types except WT showed a marked gain-of-function in voltage activation and a smaller loss-of-function in single channel conductance, with both becoming more pronounced as the number of mutant subunits per tetrameric channel increased. The molecular phenotype suggested codominance for the two homomeric channels and partial dominance for the hybrid channels. A model in which BK channels are randomly assembled from mutant and WT subunits, with each subunit contributing increments of activation and conductance, approximated the molecular phenotype of the heterozygous G375R mutation.
Competing Interest Statement
The authors have declared no competing interest.
Footnotes
1) The previous version used the Xenopus oocyte expression system to study the action of the heterozygous G375R mutation of the alpha subunit of the BK channel. The new version shows that similar pathogenic results are found in both the Xenopus oocyte and the HEK293 expression systems. 2) The classification of the mutation with regard to disease is now done at the protein level, as changes in ionic currents through mutant channels, obtaining dominant positive because the mutant channels are more active. In the previous version the classification was done at the level of the organism obtaining dominant negative due to the extreme negative effect of the mutation on fitness of the organism. Both classifications are valid but classify at different levels of the organism. 3) Models are now presented in the revised version that account for the relatively independent simultaneous action of each mutant and WT subunit on the shift in voltage activation and the decrease in single channel conductance. 4) There has been extensive rewriting of much of the manuscript.
