title: Homo- and heterotetrameric architecture of the epithelial Ca2+ channels TRPV5 and TRPV6.
abstract: The molecular assembly of the epithelial Ca(2+) channels (TRPV5 and TRPV6) was investigated to determine the subunit stoichiometry and composition. Immunoblot analysis of Xenopus laevis oocytes expressing TRPV5 and TRPV6 revealed two specific bands of 75 and 85-100 kDa, corresponding to the core and glycosylated proteins, respectively, for each channel. Subsequently, membranes of these oocytes were sedimented on sucrose gradients. Immuno blotting revealed that TRPV5 and TRPV6 complexes migrate with a mol. wt of 400 kDa, in line with a tetrameric structure. The tetrameric stoichiometry was confirmed in an electrophysiological analysis of HEK293 cells co-expressing concatemeric channels together with a TRPV5 pore mutant that reduced Cd(2+) sensitivity and voltage-dependent gating. Immuno precipitations using membrane fractions from oocytes co-expressing TRPV5 and TRPV6 demonstrated that both channels can form heteromeric complexes. Expression of all possible heterotetrameric TRPV5/6 complexes in HEK293 cells resulted in Ca(2+) channels that varied with respect to Ca(2+)-dependent inactivation, Ba(2+) selectivity and pharmacological block. Thus, Ca(2+)-transporting epithelia co-expressing TRPV5 and TRPV6 can generate a pleiotropic set of functional heterotetrameric channels with different Ca(2+) transport kinetics.
authors.affiliation: Department of Cell Physiology, Nijmegen Centre for Molecular Life Sciences, University Medical Centre Nijmegen, PO Box 9101, NL-6500 HB Nijmegen, The Netherlands.
authors.forename: J G J
authors.initials: JG
authors.lastname: Hoenderop
authors.forename: T
authors.initials: T
authors.lastname: Voets
authors.forename: S
authors.initials: S
authors.lastname: Hoefs
authors.forename: F
authors.initials: F
authors.lastname: Weidema
authors.forename: J
authors.initials: J
authors.lastname: Prenen
authors.forename: B
authors.initials: B
authors.lastname: Nilius
authors.forename: R J M
authors.initials: RJ
authors.lastname: Bindels
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000737:chemistry* / Q000378:metabolism; D004848:Epithelium / Q000737:chemistry / Q000378:metabolism*; D007668:Kidney / Q000737:chemistry / Q000378:metabolism; D051379:Mice; D011233:Precipitin Tests; D017434:Protein Structure, Tertiary; D050916:TRPV Cation Channels
chemical_list: D015220:Calcium Channels; D050916:TRPV Cation Channels; C120776:TRPV6 channel; C492240:Trpv5 protein, mouse; C446923:Trpv6 protein, mouse; D002118:Calcium