Structure-Function Analysis of CALX1.1, a Na+-Ca2+ Exchanger fromDrosophila

Abstract

Cytoplasmic Na

Targeting and Stability of Na/Ca Exchanger 1 in Cardiomyocytes Requires Direct Interaction with the Membrane Adaptor Ankyrin-B

“…Notably, these studies have identified a number of intracellular factors that bind to and regulate Na/Ca exchanger transport activity. These factors include both calcium and sodium ions, as well as protons, phosphatidylinositol 4,5-bisphosphate (PIP 2 ), inhibitor peptide (XIP), ATP, and proteases (42)(43)(44)(45)(46)(47)(48)(49)(50)(51)(52)(53)(54).…”

Effects of SEA0400 on Mutant NCX1.1 Na+-Ca2+Exchangers with Altered Ionic Regulation

“…Mutations were generated using the Sculptor in vitro mutagenesis kit (Amersham Biosciences) as described previously (Matsuoka et al, 1997;Dyck et al, 1998). Generally, two types of mutations were examined to determine the involvement of I 1 and I 2 inactivation in block of NCX1.1 currents by SEA.…”

“…Structure-function analyses of NCX1.1 and CALX1.1, a Na ϩ -Ca 2ϩ exchanger from Drosophila melanogaster, have provided important information delineating the protein domains involved in I 1 and I 2 inactivation (Matsuoka et al, 1997;Dyck et al, 1998). Regulation of Na tivation is thought to involve amino acids 219 to 238 of NCX1.1, the so-called XIP region, located at the N terminus of the large cytoplasmic loop of the exchanger (Matsuoka et al, 1997).…”

“…Similar results have been obtained with CALX1.1 bearing mutations at the analogous positions within its amino acid sequence . A high-affinity Ca 2ϩ binding site that modulates I 2 inactivation is also located in the large intracellular loop of NCX1.1 and CALX1.1 (Levitsky et al, 1994;Matsuoka et al, 1995;Dyck et al, 1998 (Matsuda et al, 2001;Tanaka et al, 2002;Lee et al, 2003) have shown that SEA0400 (SEA) inhibits NCX1.1 with high affinity (IC 50 Ϸ 23 nM) and confers considerable protective effects against cardiovascular and cerebral ischemia. One potentially important characteristic of SEA action is that it may block Na ϩ -Ca 2ϩ exchange in a mode-selective manner.…”

“…In this study, we have investigated the effects of SEA using mutant NCX1.1 exchangers that exhibit altered ionic regulatory properties. Three distinct categories of mutations were selected for study so that the blocking effects of SEA could be investigated with mutants displaying either enhanced or depressed I 1 inactivation, as well as with a mutant displaying suppressed I 2 inactivation (Matsuoka et al, 1997;Dyck et al, 1998;Maxwell et al, 1999). The data obtained show clearly that SEA blocks NCX1.1 by mimicking or promoting entry of Na ϩ -Ca 2ϩ exchange molecules into the I 1 , but not the I 2 , inactive state.…”