Structural highlights
Publication Abstract from PubMedPreviously, we reported an acidification-dependent interaction of the endosomal V-ATPase with cytohesin-2, a GDP/GTP-exchange factor (GEF), suggesting that it functions as a pH-sensing receptor. Here, we have studied the molecular mechanism of signaling between the V-ATPase, cytohesin-2 and Arf GTP-binding proteins. We found that part of the N-terminal cytosolic tail of the V-ATPase a2-subunit (a2N), corresponding to its first seventeen amino acids (a2N(1-17)), potently modulates the enzymatic GDP/GTP-exchange activity of cytohesin-2. Moreover, this peptide strongly inhibits GEF-activity via direct interaction with the Sec7 domain of cytohesin-2. The structure of a2N(1-17) and its amino acids F(5), M(10) and Q(14) involved in interaction with Sec7 domain were determined by NMR spectroscopy analysis. In silico docking experiments revealed that part of the V-ATPase formed by its a2N(1-17) epitope competes with the Switch 2 region of Arf1 and Arf6 for binding to the Sec7 domain of cytohesin-2. The amino acid sequence alignment and GEF-activity studies also uncovered the conserved character of signaling between all four (a1-a4) a-subunit isoforms of mammalian V-ATPase and cytohesin-2. Moreover, the conserved character of this phenomenon was also confirmed in experiments showing binding of mammalian cytohesin-2 to the intact yeast V-ATPase holo-complex. Thus, here we have uncovered an evolutionarily conserved function of the V-ATPase as a novel cytohesin-signaling receptor. The N-terminus of a-Subunit Isoforms is Involved in Signaling between V-ATPase and Cytohesin-2.,Hosokawa H, Dip PV, Merkulova M, Bakulina A, Zhuang Z, Khatri A, Jian X, Keating SM, Bueler SA, Rubinstein JL, Randazzo PA, Ausiello DA, Gruber G, Marshansky V J Biol Chem. 2013 Jan 3. PMID:23288846[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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