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

Cytoplasmic Na+ and Ca2+ regulate the activity of Na+-Ca2+ exchange proteins, in addition to serving as the transported ions, and protein regions involved in these processes have been identified for the canine cardiac Na+-Ca2+ exchanger, NCX1.1. Although protein regions associated with Na+i- and Ca2+i-dependent regulation are highly conserved among cloned Na+-Ca2+ exchangers, it is unknown whether or not the structure-function relationships characteristic of NCX1.1 apply to any other exchangers. Therefore, we studied structure-function relationships in a Na+-Ca2+ exchanger from Drosophila, CALX1.1, which is unique among characterized members of this family of proteins in that μm levels of Ca2+i inhibit exchange current. Wild-type and mutant CALX1.1 exchangers were expressed in Xenopus oocytes and characterized electrophysiologically using the giant excised patch technique. Mutations within the putative regulatory Ca2+i binding site of CALX1.1, like corresponding alterations in NCX1.1, led to reduced ability (i.e. D516V and D550I) or inability (i.e. G555P) of Ca2+i to inhibit Na+-Ca2+exchange activity. Similarly, mutations within the putative XIP region of CALX1.1, as in NCX1.1, led to two distinct phenotypes: acceleration (i.e. K306Q) and elimination (i.e. Δ310–313) of Na+i-dependent inactivation. These results indicate that the respective regulatory roles of the Ca2+i binding site and XIP region are conserved between CALX1.1 and NCX1.1, despite opposite responses to Ca2+i. We extended these findings using chimeric constructs of CALX1.1 and NCX1.1 to determine whether or not functional interconversion of Ca2+i regulatory phenotypes was feasible. With one chimera (i.e. CALX:NCX:CALX), substitution of a 193-amino acid segment, from the large intracellular loop of NCX1.1, for the corresponding 177-amino acid segment of CALX1.1 led to an exchanger that was stimulated by Ca2+i. This result indicates that the regulatory Ca2+i binding site of NCX1.1 retains function in a CALX1.1 parent transporter and that the substituted segment contains some of the amino acid sequence(s) required for transduction of the Ca2+i binding signal. Cytoplasmic Na+ and Ca2+ regulate the activity of Na+-Ca2+ exchange proteins, in addition to serving as the transported ions, and protein regions involved in these processes have been identified for the canine cardiac Na+-Ca2+ exchanger, NCX1.1. Although protein regions associated with Na+i- and Ca2+i-dependent regulation are highly conserved among cloned Na+-Ca2+ exchangers, it is unknown whether or not the structure-function relationships characteristic of NCX1.1 apply to any other exchangers. Therefore, we studied structure-function relationships in a Na+-Ca2+ exchanger from Drosophila, CALX1.1, which is unique among characterized members of this family of proteins in that μm levels of Ca2+i inhibit exchange current. Wild-type and mutant CALX1.1 exchangers were expressed in Xenopus oocytes and characterized electrophysiologically using the giant excised patch technique. Mutations within the putative regulatory Ca2+i binding site of CALX1.1, like corresponding alterations in NCX1.1, led to reduced ability (i.e. D516V and D550I) or inability (i.e. G555P) of Ca2+i to inhibit Na+-Ca2+exchange activity. Similarly, mutations within the putative XIP region of CALX1.1, as in NCX1.1, led to two distinct phenotypes: acceleration (i.e. K306Q) and elimination (i.e. Δ310–313) of Na+i-dependent inactivation. These results indicate that the respective regulatory roles of the Ca2+i binding site and XIP region are conserved between CALX1.1 and NCX1.1, despite opposite responses to Ca2+i. We extended these findings using chimeric constructs of CALX1.1 and NCX1.1 to determine whether or not functional interconversion of Ca2+i regulatory phenotypes was feasible. With one chimera (i.e. CALX:NCX:CALX), substitution of a 193-amino acid segment, from the large intracellular loop of NCX1.1, for the corresponding 177-amino acid segment of CALX1.1 led to an exchanger that was stimulated by Ca2+i. This result indicates that the regulatory Ca2+i binding site of NCX1.1 retains function in a CALX1.1 parent transporter and that the substituted segment contains some of the amino acid sequence(s) required for transduction of the Ca2+i binding signal. The identification of novel Na+-Ca2+exchange proteins has proceeded rapidly in the past 8 years. The family of Na+-Ca2+ exchangers includes transporters encoded by unique gene products (1Nicoll D.A. Longoni D.A. D.A. as as by a of D.A. the of exchangers have been and in have been D.A. exchangers have been cloned from and and the for structure-function of this family of D.A. of Na+-Ca2+ exchange activity by has been with the the studied the identified in the giant Ca2+i-dependent regulation is as a of Na+-Ca2+ exchange in to μm levels of The for this is to of the exchanger protein an of Ca2+i Ca2+i binding site has been identified for the canine cardiac exchanger, NCX1.1, which to associated with the Ca2+i-dependent regulatory This site a acid segment of the large intracellular loop of of within this region to in binding to proteins D.A. and the for functional Ca2+i regulation as electrophysiologically D.A. cardiac Na+-Ca2+ exchanger an in to the of This Na+i-dependent or is to and the exchanger exchanger exchanger region the of the large loop of NCX1.1 D.A. This amino acid was identified with binding (1Nicoll D.A. Longoni of a corresponding to this amino acid (i.e. to the intracellular of excised of Na+-Ca2+ exchange D.A. D.A. have that mutations within the XIP region of NCX1.1 are associated with alterations in the and of D.A. to the that the XIP region of NCX1.1 is involved in the of Na+i-dependent and that of XIP this of the regulatory and by of with NCX1.1 a exchanger the of and regulation in Na+-Ca2+ exchange function processes in between and regulation has been in structure-function and D.A. D.A. We have in and regulation for of and The that has these regulatory that it is and the structure-function of the Na+-Ca2+ exchanger have been to NCX1.1 D.A. D.A. D.A. D.A. D.A. and it is unknown whether or not these findings extended to other members of this family of we chimeric exchanger and to amino acid involved in regulatory of CALX1.1, a Na+-Ca2+ exchanger The was for it is unique among characterized exchangers in of regulatory to Ca2+i D.A. for of CALX1.1 were or regions to the regulatory Ca2+i binding site and XIP region of NCX1.1, and we in of regulatory between the two exchangers. results indicate that CALX1.1 and NCX1.1 an site for binding of regulatory Ca2+i. regions of the CALX1.1 loop were identified that Ca2+i Mutations within the XIP region the of Na+i-dependent to that for NCX1.1. results indicate that amino acid Na+i- and Ca2+i-dependent regulatory processes are conserved between CALX1.1 and NCX1.1, of the that these exchangers are by Ca2+i in this we have regulation of Na+-Ca2+ exchanger CALX1.1 using and results indicate that Ca2+i regulation in NCX1.1 and CALX1.1 to the regulatory Ca2+i binding these exchangers opposite of Ca2+i we have mutations in the XIP region of CALX1.1 and functional to that in NCX1.1. These mutations the of in Na+i-dependent from an acceleration to We have not to in of CALX1.1 and NCX1.1, to the that identified functional are are highly of this the unique Ca2+i regulatory phenotypes between these exchangers in an as of the results with chimeric exchangers, we have been in a Ca2+i regulatory to a CALX1.1 parent transporter by a of loop with the corresponding region from NCX1.1. of this region the transduction of the Ca2+i binding of of Na+-Ca2+ exchange by Ca2+i has been in exchangers studied to the unique exchanger D.A. D.A. and and With the of of Ca2+i exchange current. CALX1.1 and are unique in that exchange activity is the of and D.A. Although the of the regulatory Ca2+i binding site identified in NCX1.1 is among exchangers, have been to determine whether or not this site a function in other exchangers. we for an exchanger, CALX1.1, with a Ca2+i regulatory opposite to that of NCX1.1 for two the site a functional in NCX1.1 and CALX1.1, we that by we that the acid Ca2+i binding of NCX1.1 some of the amino acid for transduction of the Ca2+i binding this region between CALX1.1 and NCX1.1 the of in the results that mutations within the regulatory Ca2+i binding site of CALX1.1 to in the ability of Ca2+i to regulate exchange activity. of corresponding amino acid the for Ca2+i of whether the regulatory is (i.e. or (i.e. This result that the function of the Ca2+i binding site is in exchangers. the of amino acid between the within the putative Ca2+i binding of exchanger and in and results a conserved functional for exchangers and opposite Ca2+i-dependent regulatory it that the regulatory site the function in not Na+-Ca2+ of have that the XIP region a in CALX1.1 and NCX1.1 mutations phenotypes in exchangers. With corresponding to in NCX1.1 D.A. and from the was by a in the of as by a of the of to exchange current. to the for by the of with CALX1.1 a for the with The that is reduced for indicates that the has been the was in a result to that with the corresponding mutant in NCX1.1, D.A. and with CALX1.1 Although the of within the regions of the exchangers in is for the of the Ca2+i binding site it is to that this region a function in the of Na+i-dependent of Na+-Ca2+ exchangers in This is by the that CALX1.1 D.A. and D.A. like NCX1.1, are by which to the and the function of the XIP region and Ca2+i binding site to conserved between CALX1.1 and NCX1.1, we have for the in Ca2+i-dependent regulatory we that mutations exchangers to in CALX1.1 and in D.A. D.A. of is that Ca2+i to these exchangers the transduction has been this is a by D.A. that a protein the site of NCX1.1, a from the with this is result with the chimeric exchanger of the Ca2+i binding site and of NCX1.1 with the corresponding region of CALX1.1 led to a transporter that was stimulated by regulatory Ca2+i the Ca2+i binding function to have been and a interconversion of phenotypes Although of results from and chimeric proteins to the exchanger with the findings that Ca2+i binding to the within the Ca2+i binding and that transduction of the Ca2+i binding or distinct from this results with this of the that the chimeric protein a novel Although is to indicate that Ca2+i binding and transduction are or results are of this we that the alterations associated with these two are with to the function and Na+i-dependent regulation of the parent and of Ca2+i-dependent regulatory phenotypes between CALX1.1 and NCX1.1 of this The identification of novel Na+-Ca2+exchange proteins has proceeded rapidly in the past 8 years. The family of Na+-Ca2+ exchangers includes transporters encoded by unique gene products (1Nicoll D.A. Longoni D.A. D.A. as as by a of D.A. the of exchangers have been and in have been D.A. exchangers have been cloned from and and the for structure-function of this family of D.A. of Na+-Ca2+ exchange activity by has been with the the studied the identified in the giant Ca2+i-dependent regulation is as a of Na+-Ca2+ exchange in to μm levels of The for this is to of the exchanger protein an of Ca2+i Ca2+i binding site has been identified for the canine cardiac exchanger, NCX1.1, which to associated with the Ca2+i-dependent regulatory This site a acid segment of the large intracellular loop of of within this region to in binding to proteins D.A. and the for functional Ca2+i regulation as electrophysiologically D.A. The cardiac Na+-Ca2+ exchanger an in to the of This Na+i-dependent or is to and the exchanger exchanger exchanger region the of the large loop of NCX1.1 D.A. This amino acid was identified with binding (1Nicoll D.A. Longoni of a corresponding to this amino acid (i.e. to the intracellular of excised of Na+-Ca2+ exchange D.A. D.A. have that mutations within the XIP region of NCX1.1 are associated with alterations in the and of D.A. to the that the XIP region of NCX1.1 is involved in the of Na+i-dependent and that of XIP this of the regulatory and by of with NCX1.1 a exchanger Although the of and regulation in Na+-Ca2+ exchange function processes in between and regulation has been in structure-function and D.A. D.A. We have in and regulation for of and The that has these regulatory that it is and the structure-function of the Na+-Ca2+ exchanger have been to NCX1.1 D.A. D.A. D.A. D.A. D.A. and it is unknown whether or not these findings extended to other members of this family of we chimeric exchanger and to amino acid involved in regulatory of CALX1.1, a Na+-Ca2+ exchanger The was for it is unique among characterized exchangers in of regulatory to Ca2+i D.A. for of CALX1.1 were or regions to the regulatory Ca2+i binding site and XIP region of NCX1.1, and we in of regulatory between the two exchangers. results indicate that CALX1.1 and NCX1.1 an site for binding of regulatory Ca2+i. regions of the CALX1.1 loop were identified that Ca2+i Mutations within the XIP region the of Na+i-dependent to that for NCX1.1. results indicate that amino acid Na+i- and Ca2+i-dependent regulatory processes are conserved between CALX1.1 and NCX1.1, of the that these exchangers are by Ca2+i in this we have regulation of Na+-Ca2+ exchanger CALX1.1 using and results indicate that Ca2+i regulation in NCX1.1 and CALX1.1 to the regulatory Ca2+i binding these exchangers opposite of Ca2+i we have mutations in the XIP region of CALX1.1 and functional to that in NCX1.1. These mutations the of in Na+i-dependent from an acceleration to We have not to in of CALX1.1 and NCX1.1, to the that identified functional are are highly of this the unique Ca2+i regulatory phenotypes between these exchangers in an as of the results with chimeric exchangers, we have been in a Ca2+i regulatory to a CALX1.1 parent transporter by a of loop with the corresponding region from NCX1.1. of this region the transduction of the Ca2+i binding of of Na+-Ca2+ exchange by Ca2+i has been in exchangers studied to the unique exchanger D.A. D.A. and and With the of of Ca2+i exchange current. CALX1.1 and are unique in that exchange activity is the of and D.A. Although the of the regulatory Ca2+i binding site identified in NCX1.1 is among exchangers, have been to determine whether or not this site a function in other exchangers. we for an exchanger, CALX1.1, with a Ca2+i regulatory opposite to that of NCX1.1 for two the site a functional in NCX1.1 and CALX1.1, we that by we that the acid Ca2+i binding of NCX1.1 some of the amino acid for transduction of the Ca2+i binding this region between CALX1.1 and NCX1.1 the of in the results that mutations within the regulatory Ca2+i binding site of CALX1.1 to in the ability of Ca2+i to regulate exchange activity. of corresponding amino acid the for Ca2+i of whether the regulatory is (i.e. or (i.e. This result that the function of the Ca2+i binding site is in exchangers. the of amino acid between the within the putative Ca2+i binding of exchanger and in and results a conserved functional for exchangers and opposite Ca2+i-dependent regulatory it that the regulatory site the function in not Na+-Ca2+ of have that the XIP region a in CALX1.1 and NCX1.1 mutations phenotypes in exchangers. With corresponding to in NCX1.1 D.A. and from the was by a in the of as by a of the of to exchange current. to the for by the of with CALX1.1 a for the with The that is reduced for indicates that the has been the was in a result to that with the corresponding mutant in NCX1.1, D.A. and with CALX1.1 Although the of within the regions of the exchangers in is for the of the Ca2+i binding site it is to that this region a function in the of Na+i-dependent of Na+-Ca2+ exchangers in This is by the that CALX1.1 D.A. and D.A. like NCX1.1, are by which to the and the function of the XIP region and Ca2+i binding site to conserved between CALX1.1 and NCX1.1, we have for the in Ca2+i-dependent regulatory we that mutations exchangers to in CALX1.1 and in D.A. D.A. of is that Ca2+i to these exchangers the transduction has been this is a by D.A. that a protein the site of NCX1.1, a from the with this is result with the chimeric exchanger of the Ca2+i binding site and of NCX1.1 with the corresponding region of CALX1.1 led to a transporter that was stimulated by regulatory Ca2+i the Ca2+i binding function to have been and a interconversion of phenotypes Although of results from and chimeric proteins to the exchanger with the findings that Ca2+i binding to the within the Ca2+i binding and that transduction of the Ca2+i binding or distinct from this results with this of the that the chimeric protein a novel Although is to indicate that Ca2+i binding and transduction are or results are of this we that the alterations associated with these two are with to the function and Na+i-dependent regulation of the parent and of Ca2+i-dependent regulatory phenotypes between CALX1.1 and NCX1.1 of this this we have regulation of Na+-Ca2+ exchanger CALX1.1 using and results indicate that Ca2+i regulation in NCX1.1 and CALX1.1 to the regulatory Ca2+i binding these exchangers opposite of Ca2+i we have mutations in the XIP region of CALX1.1 and functional to that in NCX1.1. These mutations the of in Na+i-dependent from an acceleration to We have not to in of CALX1.1 and NCX1.1, to the that identified functional are are highly of this the unique Ca2+i regulatory phenotypes between these exchangers in an as of the results with chimeric exchangers, we have been in a Ca2+i regulatory to a CALX1.1 parent transporter by a of loop with the corresponding region from NCX1.1. of this region the transduction of the Ca2+i binding signal. Ca2+i-dependent of of Na+-Ca2+ exchange by Ca2+i has been in exchangers studied to the unique exchanger D.A. D.A. and and With the of of Ca2+i exchange current. CALX1.1 and are unique in that exchange activity is the of and D.A. Although the of the regulatory Ca2+i binding site identified in NCX1.1 is among exchangers, have been to determine whether or not this site a function in other exchangers. we for an exchanger, CALX1.1, with a Ca2+i regulatory opposite to that of NCX1.1 for two the site a functional in NCX1.1 and CALX1.1, we that by we that the acid Ca2+i binding of NCX1.1 some of the amino acid for transduction of the Ca2+i binding this region between CALX1.1 and NCX1.1 the of in the results that mutations within the regulatory Ca2+i binding site of CALX1.1 to in the ability of Ca2+i to regulate exchange activity. of corresponding amino acid the for Ca2+i of whether the regulatory is (i.e. or (i.e. This result that the function of the Ca2+i binding site is in exchangers. the of amino acid between the within the putative Ca2+i binding of exchanger and in and results a conserved functional for exchangers and opposite Ca2+i-dependent regulatory it that the regulatory site the function in not Na+-Ca2+ of have that the XIP region a in CALX1.1 and NCX1.1 mutations phenotypes in exchangers. With corresponding to in NCX1.1 D.A. and from the was by a in the of as by a of the of to exchange current. to the for by the of with CALX1.1 a for the with The that is reduced for indicates that the has been the was in a result to that with the corresponding mutant in NCX1.1, D.A. and with CALX1.1 Although the of within the regions of the exchangers in is for the of the Ca2+i binding site it is to that this region a function in the of Na+i-dependent of Na+-Ca2+ exchangers in This is by the that CALX1.1 D.A. and D.A. like NCX1.1, are by which to the and the function of the XIP region and Ca2+i binding site to conserved between CALX1.1 and NCX1.1, we have for the in Ca2+i-dependent regulatory we that mutations exchangers to in CALX1.1 and in D.A. D.A. of is that Ca2+i to these exchangers the transduction has been this is a by D.A. that a protein the site of NCX1.1, a from the with this is result with the chimeric exchanger of the Ca2+i binding site and of NCX1.1 with the corresponding region of CALX1.1 led to a transporter that was stimulated by regulatory Ca2+i the Ca2+i binding function to have been and a interconversion of phenotypes Although of results from and chimeric proteins to the exchanger with the findings that Ca2+i binding to the within the Ca2+i binding and that transduction of the Ca2+i binding or distinct from this results with this of the that the chimeric protein a novel Although is to indicate that Ca2+i binding and transduction are or results are of this we that the alterations associated with these two are with to the function and Na+i-dependent regulation of the parent and of Ca2+i-dependent regulatory phenotypes between CALX1.1 and NCX1.1 of this Ca2+i-dependent of of Na+-Ca2+ exchange by Ca2+i has been in exchangers studied to the unique exchanger D.A. D.A. and and With the of of Ca2+i exchange current. CALX1.1 and are unique in that exchange activity is the of and D.A. Although the of the regulatory Ca2+i binding site identified in NCX1.1 is among exchangers, have been to determine whether or not this site a function in other exchangers. we for an exchanger, CALX1.1, with a Ca2+i regulatory opposite to that of NCX1.1 for two the site a functional in NCX1.1 and CALX1.1, we that by we that the acid Ca2+i binding of NCX1.1 some of the amino acid for transduction of the Ca2+i binding this region between CALX1.1 and NCX1.1 the of in the results that mutations within the regulatory Ca2+i binding site of CALX1.1 to in the ability of Ca2+i to regulate exchange activity. of corresponding amino acid the for Ca2+i of whether the regulatory is (i.e. or (i.e. This result that the function of the Ca2+i binding site is in exchangers. the of amino acid between the within the putative Ca2+i binding of exchanger and in and results a conserved functional for exchangers and opposite Ca2+i-dependent regulatory it that the regulatory site the function in not Na+-Ca2+ of have that the XIP region a in CALX1.1 and NCX1.1 mutations phenotypes in exchangers. With corresponding to in NCX1.1 D.A. and from the was by a in the of as by a of the of to exchange current. to the for by the of with CALX1.1 a for the with The that is reduced for indicates that the has been the was in a result to that with the corresponding mutant in NCX1.1, D.A. and with CALX1.1 Although the of within the regions of the exchangers in is for the of the Ca2+i binding site it is to that this region a function in the of Na+i-dependent of Na+-Ca2+ exchangers in This is by the that CALX1.1 D.A. and D.A. like NCX1.1, are by which to the and the function of the XIP region and Ca2+i binding site to conserved between CALX1.1 and NCX1.1, we have for the in Ca2+i-dependent regulatory we that mutations exchangers to in CALX1.1 and in D.A. D.A. of is that Ca2+i to these exchangers the transduction has been this is a by D.A. that a protein the site of NCX1.1, a from the with this is result with the chimeric exchanger of the Ca2+i binding site and of NCX1.1 with the corresponding region of CALX1.1 led to a transporter that was stimulated by regulatory Ca2+i the Ca2+i binding function to have been and a interconversion of phenotypes Although of results from and chimeric proteins to the exchanger with the findings that Ca2+i binding to the within the Ca2+i binding and that transduction of the Ca2+i binding or distinct from this results with this of the that the chimeric protein a novel Although is to indicate that Ca2+i binding and transduction are or results are of this we that the alterations associated with these two are with to the function and Na+i-dependent regulation of the parent and of Ca2+i-dependent regulatory phenotypes between CALX1.1 and NCX1.1 of this Ca2+i-dependent of of Na+-Ca2+ exchange by Ca2+i has been in exchangers studied to the unique exchanger D.A. D.A. and and With the of of Ca2+i exchange current. CALX1.1 and are unique in that exchange activity is the of and D.A. Although the of the regulatory Ca2+i binding site identified in NCX1.1 is among exchangers, have been to determine whether or not this site a function in other exchangers. we for an exchanger, CALX1.1, with a Ca2+i regulatory opposite to that of NCX1.1 for two the site a functional in NCX1.1 and CALX1.1, we that by we that the acid Ca2+i binding of NCX1.1 some of the amino acid for transduction of the Ca2+i binding this region between CALX1.1 and NCX1.1 the of in the results that mutations within the regulatory Ca2+i binding site of CALX1.1 to in the ability of Ca2+i to regulate exchange activity. of corresponding amino acid the for Ca2+i of whether the regulatory is (i.e. or (i.e. This result that the function of the Ca2+i binding site is in exchangers. the of amino acid between the within the putative Ca2+i binding of exchanger and in and results a conserved functional for exchangers and opposite Ca2+i-dependent regulatory it that the regulatory site the function in not Na+-Ca2+ exchangers. of Na+-Ca2+ exchange by Ca2+i has been in exchangers studied to the unique exchanger D.A. D.A. and and With the of of Ca2+i exchange current. CALX1.1 and are unique in that exchange activity is the of and D.A. Although the of the regulatory Ca2+i binding site identified in NCX1.1 is among exchangers, have been to determine whether or not this site a function in other exchangers. we for an exchanger, CALX1.1, with a Ca2+i regulatory opposite to that of NCX1.1 for two the site a functional in NCX1.1 and CALX1.1, we that by we that the acid Ca2+i binding of NCX1.1 some of the amino acid for transduction of the Ca2+i binding this region between CALX1.1 and NCX1.1 the of in the results that mutations within the regulatory Ca2+i binding site of CALX1.1 to in the ability of Ca2+i to regulate exchange activity. of corresponding amino acid the for Ca2+i of whether the regulatory is (i.e. or (i.e. This result that the function of the Ca2+i binding site is in exchangers. the of amino acid between the within the putative Ca2+i binding of exchanger and in and results a conserved functional for exchangers and opposite Ca2+i-dependent regulatory it that the regulatory site the function in not Na+-Ca2+ exchangers. Na+i-dependent of have that the XIP region a in CALX1.1 and NCX1.1 mutations phenotypes in exchangers. With corresponding to in NCX1.1 D.A. and from the was by a in the of as by a of the of to exchange current. to the for by the of with CALX1.1 a for the with The that is reduced for indicates that the has been the was in a result to that with the corresponding mutant in NCX1.1, D.A. and with CALX1.1 Although the of within the regions of the exchangers in is for the of the Ca2+i binding site it is to that this region a function in the of Na+i-dependent of Na+-Ca2+ exchangers in This is by the that CALX1.1 D.A. and D.A. like NCX1.1, are by which to the We have that the XIP region a in CALX1.1 and NCX1.1 mutations phenotypes in exchangers. With corresponding to in NCX1.1 D.A. and from the was by a in the of as by a of the of to exchange current. to the for by the of with CALX1.1 a for the with The that is reduced for indicates that the has been the was in a result to that with the corresponding mutant in NCX1.1, D.A. and with CALX1.1 Although the of within the regions of the exchangers in is for the of the Ca2+i binding site it is to that this region a function in the of Na+i-dependent of Na+-Ca2+ exchangers in This is by the that CALX1.1 D.A. and D.A. like NCX1.1, are by which to the and the function of the XIP region and Ca2+i binding site to conserved between CALX1.1 and NCX1.1, we have for the in Ca2+i-dependent regulatory we that mutations exchangers to in CALX1.1 and in D.A. D.A. of is that Ca2+i to these exchangers the transduction has been this is a by D.A. that a protein the site of NCX1.1, a from the with this is result with the chimeric exchanger of the Ca2+i binding site and of NCX1.1 with the corresponding region of CALX1.1 led to a transporter that was stimulated by regulatory Ca2+i the Ca2+i binding function to have been and a interconversion of phenotypes Although of results from and chimeric proteins to the exchanger with the findings that Ca2+i binding to the within the Ca2+i binding and that transduction of the Ca2+i binding or distinct from this results with this of the that the chimeric protein a novel Although is to indicate that Ca2+i binding and transduction are or results are of this we that the alterations associated with these two are with to the function and Na+i-dependent regulation of the parent and of Ca2+i-dependent regulatory phenotypes between CALX1.1 and NCX1.1 of this Although the function of the XIP region and Ca2+i binding site to conserved between CALX1.1 and NCX1.1, we have for the in Ca2+i-dependent regulatory we that mutations exchangers to in CALX1.1 and in D.A. D.A. of is that Ca2+i to these exchangers the transduction has been this is a by D.A. that a protein the site of NCX1.1, a from the with this is result with the chimeric exchanger of the Ca2+i binding site and of NCX1.1 with the corresponding region of CALX1.1 led to a transporter that was stimulated by regulatory Ca2+i the Ca2+i binding function to have been and a interconversion of phenotypes Although of results from and chimeric proteins to the exchanger with the findings that Ca2+i binding to the within the Ca2+i binding and that transduction of the Ca2+i binding or distinct from this results with this of the that the chimeric protein a novel Although is to indicate that Ca2+i binding and transduction are or results are of this we that the alterations associated with these two are with to the function and Na+i-dependent regulation of the parent and of Ca2+i-dependent regulatory phenotypes between CALX1.1 and NCX1.1 of this We and for with for NCX1.1 and