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The single pore residue Asp542 determines Ca2+ permeation and Mg2+ block of the epithelial Ca2+ channel Nilius B; Vennekens R; Prenen J; Hoenderop JG; Droogmans G; Bindels RJJ Biol Chem 2001[Jan]; 276 (2): 1020-5The 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.|*Aspartic Acid[MESH]|Amino Acid Sequence[MESH]|Amino Acid Substitution[MESH]|Animals[MESH]|Calcium Channels/*chemistry/drug effects/*physiology[MESH]|Calcium/*metabolism[MESH]|Humans[MESH]|Kidney/metabolism[MESH]|Kinetics[MESH]|Magnesium/*pharmacology[MESH]|Membrane Potentials/drug effects/physiology[MESH]|Mice[MESH]|Models, Molecular[MESH]|Molecular Sequence Data[MESH]|Mutagenesis, Site-Directed[MESH]|Protein Structure, Secondary[MESH]|Rabbits[MESH]|Recombinant Proteins/chemistry/drug effects/metabolism[MESH]|Sequence Alignment[MESH]|Sequence Homology, Amino Acid[MESH]|TRPV Cation Channels[MESH]|Transfection[MESH] |
