Accessory Protein Facilitated CFTR-CFTR Interaction, a Molecular Mechanism to Potentiate the Chloride Channel Activity

Abstract

The cystic fibrosis transmembrane conductance regulator (CFTR) gene encodes a chloride channel protein that belongs to the superfamily of ATP binding cassette (ABC) transporters. Phosphorylation by protein kinase A in the presence of ATP activates the CFTR-mediated chloride conductance of the apical membranes. We have identified a novel hydrophilic CFTR binding protein, CAP70, which is also concentrated on the apical surfaces. CAP70 consists of four PDZ domains, three of which are capable of binding to the CFTR C terminus. Linking at least two CFTR molecules via cytoplasmic C-terminal binding by either multivalent CAP70 or a bivalent monoclonal antibody potentiates the CFTR chloride channel activity. Thus, the CFTR channel can be switched to a more active conducting state via a modification of intermolecular CFTR-CFTR contact that is enhanced by an accessory protein.

The Multivalent PDZ Domain-containing Protein PDZK1 Regulates Transport Activity of Renal Urate-Anion Exchanger URAT1 via Its C Terminus

“…The dissociation constant (K D ) values are as follows: PDZK1 PDZ1 domain, 1.97 nM; PDZ2 domain, 514 nM; and PDZ4 domain, 296 nM for URAT1 C terminus. These binding affinities are similar to the value reported for the interaction between CAP70 and CFTR (K D ϭ 8 -220 nM) (14).…”

“…PDZK1 is a PDZ domain-containing protein that was originally identified as a protein that interacts with MAP17, a membrane-associated protein (19). In addition to MAP17, PDZK1 has also been reported to interact with several membrane proteins through its PDZ domain; these proteins include the type IIa Na/P i cotransporter (26), scavenger receptor class B type I (SR-BI) (27), CFTR (14), and multidrug resistance-associated protein MRP2 (cMOAT) (28).…”

“…These domains range from 80 to 90 amino acids in length and bind typically to proteins containing the tripeptide motif (S/T)XØ (X ϭ any amino acid and Ø ϭ a hydrophobic residue) at their C termini (9,10). These multidomain molecules not only target and provide scaffolds for protein-protein interactions but also modulate the function of receptors and ion channels, by which they associate (11)(12)(13)(14)(15)(16). The disruption of the association between PDZ proteins and their targets contributes to the pathogenesis of a number of human diseases, most probably because of the failure of PDZ proteins to appropriately target and modulate the actions of associated proteins (6).…”

ATP-binding Cassette Transporter A1 Contains a Novel C-terminal VFVNFA Motif That Is Required for Its Cholesterol Efflux and ApoA-I Binding Activities

“…This possibility is the one we currently favor. Our finding that a peptide mimetic of the VFVNFA motif inhibits ABCA-mediated cholesterol efflux, coupled with observations that other ABC transporters rely on their C termini to recruit proteins that regulate their function (41,42), make it attractive to hypothesize that this novel motif is involved in a similar protein recruitment activity. As the same motif is present in other members of the ABCA class of transporters, we speculate that these transporters may share common protein interactors that are required for their function.…”

Proteomic survey towards the tissue-specific proteins of mouse mitochondria

“…Although the results of the confocal analysis indicate that SCP2 is localized in mitochondria, our data cannot exclude the possibility that SCP2 is localized in other organelle due to the lack of evidence obtained from the specific indicators for other organelles. PDZK1 is mainly responsible for the regulation of Na + /H + exchange so that this protein is highly expressed in kidney tissue, such as the surface of the renal tubular epithelial cells [23][24][25][26]. The subcellular localization of PDZK1 has not been reported yet.…”