XXXX Interacts with the Sodium/Calcium Exchanger @entity27778 to Regulate Activity.

@entity141 @entity13609 @entity4024 @entity27778
Changes in intracellular @entity141 concentrations ([ @entity141 ]i) are an important signal for various physiological activities. The @entity4024 / @entity141 exchangers (NCX) at the plasma membrane transport @entity141 into or out of the cell according to the electrochemical gradients of @entity4024 and @entity141 to modulate [ @entity141 ]i homeostasis. @entity13609 ( @entity13609 ) senses [ @entity141 ]i changes and relays @entity141 signals by binding to target proteins such as channels and transporters. However, it is not clear how @entity13609 modulates NCX activity. Using @entity13609 as a bait, we pulled down the intracellular loops subcloned from the @entity27778 splice variants @entity27778 .1 and @entity27778 .3. This interaction requires both @entity141 and a putative @entity13609 -binding segment (CaMS). To determine whether @entity13609 modulates NCX activity, we co-expressed @entity27778 splice variants with @entity13609 or CaM1234 (a @entity141 -binding deficient mutant) in HEK293T cells and measured the increase in [ @entity141 ]i contributed by the influx of @entity141 through NCX. Deleting the CaMS from @entity27778 .1 and @entity27778 .3 attenuated exchange activity and decreased membrane localization. Without the mutually exclusive exon, the exchange activity was decreased and could be partially rescued by CaM1234. Point-mutations at any of the 4 conserved a.a. residues in the CaMS had differential effects in @entity27778 .1 and @entity27778 .3. Mutating the first two conserved a.a. in @entity27778 .1 decreased exchange activity; mutating the 3rd or 4th conserved a.a. residues did not alter exchange activity, but @entity13609 co-expression suppressed activity. Mutating the 2nd and 3rd conserved a.a. residues in @entity27778 .3 decreased exchange activity. Taken together, our results demonstrate that @entity13609 senses changes in [ @entity141 ]i and binds to the cytoplasmic loop of @entity27778 to regulate exchange activity.
