title: Identification of a multiprotein "motor" complex binding to water channel aquaporin-2.
abstract: Targeted positioning of water channel aquaporin-2 (AQP2) strictly regulates body water homeostasis. Trafficking of AQP2 to the apical membrane is critical to the reabsorption of water in renal collecting ducts. Recently, we have identified for the first time proteins which directly bind to AQP2: SPA-1, a GTPase-activating protein for Rap1, and cytoskeletal protein actin. Based on these findings, we have speculated the existence of a multiprotein complex which includes AQP2, SPA-1, and actin, for providing the mechanism which generates force and motion in AQP2 trafficking. To clarify the proteins comprising the complex, a large amount of AQP2-associated protein complex was isolated from the extract of rat kidney papilla using immunoaffinity column coupled with anti-AQP2 antibody and was analyzed by matrix-assisted laser desorption-ionization time-of-flight mass spectrometry (MALDI-TOF MS). In addition to SPA-1 and actin, 11 proteins were identified using this method: ionized calcium binding adapter molecule 2, myosin regulatory light chain smooth muscle isoforms 2-A and 2-B, alpha-tropomyosin 5b, annexin A2 and A6, scinderin, gelsolin, alpha-actinin 4, alpha-II spectrin, and myosin heavy chain nonmuscle type A. Our findings show for the first time an AQP2-binding multiprotein "force generator" complex. This multiprotein complex may provide the machinery of driving AQP2 movement.
authors.affiliation: Department of Nephrology, Tokyo Medical and Dental University, Tokyo 113-8519, Japan. ynodmed2@tmd.ac.jp
authors.forename: Yumi
authors.initials: Y
authors.lastname: Noda
authors.forename: Saburo
authors.initials: S
authors.lastname: Horikawa
authors.forename: Yoshifumi
authors.initials: Y
authors.lastname: Katayama
authors.forename: Sei
authors.initials: S
authors.lastname: Sasaki
mesh_terms: D000199:Actins / Q000378:metabolism; D000818:Animals; D051399:Aquaporin 2; D020346:Aquaporins / Q000302:isolation & purification* / Q000378:metabolism; D002845:Chromatography / Q000379:methods; D020690:GTPase-Activating Proteins / Q000302:isolation & purification / Q000378:metabolism; D066298:In Vitro Techniques; D007679:Kidney Medulla / Q000737:chemistry; D046912:Multiprotein Complexes / Q000302:isolation & purification* / Q000378:metabolism; D011485:Protein Binding; D021381:Protein Transport; D051381:Rats; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization
chemical_list: D000199:Actins; C496025:Aqp2 protein, rat; D051399:Aquaporin 2; D020346:Aquaporins; D020690:GTPase-Activating Proteins; D046912:Multiprotein Complexes