Critical loci for ion conduction in inward rectifier K+ channels are only now being discovered, The C-terminal region of IRK1 plays a crucial role in Mg-i(2+) blockade and single-channel K+ conductance. A negatively charged aspartate in the putative second transmembrane domain (position 172) is essential for time-dependent block by the cytoplasmic polyamines spermine and spermidine, We have now localized the C-terminus effect in IRK1 to a single, negatively charged residue (E224), Mutation of E224 to G, Q and S drastically reduced rectification. Furthermore, the IRK1 E224G mutation decreased block by Mg-i(2+) and spermidine and, like the E224Q mutation, caused a dramatic reduction in the apparent single-channel K+ conductance. The double mutation IRK1 D172N+ E224G was markedly insensitive to spermidine block, displaying an affinity similar to ROMK1, The results are compatible with a model in which the negatively charged residue at position 224, E224, is a major determinant of pore properties in IRK1, By means of a specific interaction with the negatively charged residue at position 172, D172, E224 contributes to the formation of the binding pocket for Mg2+ and polyamines, a characteristic of strong inward rectifiers.
C-TERMINUS DETERMINANTS FOR MG2+ AND POLYAMINE BLOCK OF THE INWARD RECTIFIER K+ CHANNEL IRK1
TAGLIALATELA, Maurizio;
1995-01-01
Abstract
Critical loci for ion conduction in inward rectifier K+ channels are only now being discovered, The C-terminal region of IRK1 plays a crucial role in Mg-i(2+) blockade and single-channel K+ conductance. A negatively charged aspartate in the putative second transmembrane domain (position 172) is essential for time-dependent block by the cytoplasmic polyamines spermine and spermidine, We have now localized the C-terminus effect in IRK1 to a single, negatively charged residue (E224), Mutation of E224 to G, Q and S drastically reduced rectification. Furthermore, the IRK1 E224G mutation decreased block by Mg-i(2+) and spermidine and, like the E224Q mutation, caused a dramatic reduction in the apparent single-channel K+ conductance. The double mutation IRK1 D172N+ E224G was markedly insensitive to spermidine block, displaying an affinity similar to ROMK1, The results are compatible with a model in which the negatively charged residue at position 224, E224, is a major determinant of pore properties in IRK1, By means of a specific interaction with the negatively charged residue at position 172, D172, E224 contributes to the formation of the binding pocket for Mg2+ and polyamines, a characteristic of strong inward rectifiers.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
