Abstract
Spatial and temporal regulation of intracellular Ca(2+) signaling depends on localized Ca(2+) microdomains containing the requisite molecular components for Ca(2+) influx, efflux, and signal transmission. Plasma membrane Ca(2+)-ATPase (PMCA) isoforms of the "b" splice type contain predicted PDZ (PSD95/Dlg/ZO-1) interaction domains. The COOH-terminal tail of PMCA2b isolated the membrane-associated guanylate kinase (MAGUK) protein SAP97/hDlg as a binding partner in a yeast two-hybrid screen. The related MAGUKs SAP90/PSD95, PSD93/chapsyn-110, SAP97, and SAP102 all bound to the COOH-terminal tail of PMCA4b, whereas only the first three bound to the tail of PMCA2b. Coimmunoprecipitations confirmed the interaction selectivity between PMCA4b and SAP102 as opposed to the promiscuity of PMCA2b and 4b in interacting with other SAPs. Confocal immunofluorescence microscopy revealed the exclusive presence and colocalization of PMCA4b and SAP97 in the basolateral membrane of polarized Madin-Darby canine kidney epithelial cells. In hippocampal neurons, PMCA2b was abundant throughout the somatodendritic compartment and often extended into the neck and head of individual spines where it colocalized with SAP90/PSD95. These data show that PMCA "b" splice forms interact promiscuously but also with specificity with different members of the PSD95 family of SAPs. PMCA-SAP interactions may play a role in the recruitment and maintenance of the PMCA at specific membrane domains involved in local Ca(2+) regulation.
Highlights
Calcium ion (Ca2ϩ) homeostasis is crucial for cell function and survival [1]
We reported previously that PMCA4b was able to interact with high affinity with the PDZ domains of several members of the membrane-associated guanylate kinase (MAGUK) protein family, and that this interaction was dependent on the presence of the T-S-V* COOH-terminal sequence [11]
This study demonstrates that PMCA2b and 4b, and likely all other Plasma membrane Ca2؉-ATPase (PMCA) “b” splice forms, are binding partners for members of the SAP90/PSD95 family of MAGUKs
Summary
Calcium ion (Ca2ϩ) homeostasis is crucial for cell function and survival [1]. A finely controlled system of Ca2ϩ transporters, channels, and Ca2ϩ-binding proteins allows for transient increases in the intracellular free calcium concentration ([Ca2ϩ]i),1 while over the long term maintaining a low resting [Ca2ϩ]i [2]. Plasma membrane Ca2؉-ATPase (PMCA) isoforms of the “b” splice type contain predicted PDZ (PSD95/Dlg/ZO-1) interaction domains.
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