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Nilius, B. et al.

Nilius, Vennekens, Prenen, Hoenderop, Droogmans, Bindels,

The single pore residue Asp542 determines Ca2+ permeation and Mg2+ block of the epithelial Ca2+ channel.

The epithelial Ca(2+) channel ( ECaC), which was recently cloned from rabbit kidney, exhibits distinctive properties that support a facilitating role in transcellular Ca(2+) (re)absorption. ECaC is structurally related to the family of six transmembrane-spanning ion channels with a pore-forming region between S5 and S6. Using point mutants of the conserved negatively charged amino acids present in the putative pore, we have identified a single aspartate residue that determines Ca(2+) permeation of ECaC and modulation by extracellular Mg(2+). Mutation of the aspartate residue, D542A, abolishes Ca(2+) permeation and Ca(2+)-dependent current decay as well as block by extracellular Mg(2+), whereas monovalent cations still permeate the mutant channel. Variation of the side chain length in mutations D542N, D542E, and D542M attenuated Ca(2+) permeability and Ca(2+)-dependent current decay. Block of monovalent currents through ECaC by Mg(2+) was decreased. Exchanging the aspartate residue for a positively charged amino acid, D542K, resulted in a nonfunctional channel. Mutations of two neighboring negatively charged residues, i.e. Glu(535) and Asp(550), had only minor effects on Ca(2+) permeation properties.[1]

References

The single pore residue Asp542 determines Ca2+ permeation and Mg2+ block of the epithelial Ca2+ channel. Nilius, B., Vennekens, R., Prenen, J., Hoenderop, J.G., Droogmans, G., Bindels, R.J. J. Biol. Chem. (2001) [Pubmed]

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