title: Na,K-ATPase from mice lacking the gamma subunit (FXYD2) exhibits altered Na+ affinity and decreased thermal stability.
abstract: The gamma subunit of the Na,K-ATPase, a 7-kDa single-span membrane protein, is a member of the FXYD gene family. Several FXYD proteins have been shown to bind to Na,K-ATPase and modulate its properties, and each FXYD protein appears to alter enzyme kinetics differently. Different results have sometimes been obtained with different experimental systems, however. To test for effects of gamma in a native tissue environment, mice lacking a functional gamma subunit gene (Fxyd2) were generated. These mice were viable and without observable pathology. Prior work in the mouse embryo showed that gamma is expressed at the blastocyst stage. However, there was no delay in blastocele formation, and the expected Mendelian ratios of offspring were obtained even with Fxyd2-/- dams. In adult Fxyd2-/- mouse kidney, splice variants of gamma that have different nephron segment-specific expression patterns were absent. Purified gamma-deficient renal Na,K-ATPase displayed higher apparent affinity for Na+ without significant change in apparent affinity for K+. Affinity for ATP, which was expected to be decreased, was instead slightly increased. The results suggest that regulation of Na+ sensitivity is a major functional role for this protein, whereas regulation of ATP affinity may be context-specific. Most importantly, this implies that gamma and other FXYD proteins have their effects by local and not global conformation change. Na,K-ATPase lacking the gamma subunit had increased thermal lability. Combined with other evidence that gamma participates in an early step of thermal denaturation, this indicates that FXYD proteins may play an important structural role in the enzyme complex.
authors.affiliation: Department of Physiology and Pharmacology, University of Western Ontario, London, Ontario N6A 5C1, Canada.
authors.forename: D Holstead
authors.initials: DH
authors.lastname: Jones
authors.forename: Tony Y
authors.initials: TY
authors.lastname: Li
authors.forename: Elena
authors.initials: E
authors.lastname: Arystarkhova
authors.forename: Kevin J
authors.initials: KJ
authors.lastname: Barr
authors.forename: Randall K
authors.initials: RK
authors.lastname: Wetzel
authors.forename: Jun
authors.initials: J
authors.lastname: Peng
authors.forename: Kathryn
authors.initials: K
authors.lastname: Markham
authors.forename: Kathleen J
authors.initials: KJ
authors.lastname: Sweadner
authors.forename: Guo-Hua
authors.initials: GH
authors.lastname: Fong
authors.forename: Gerald M
authors.initials: GM
authors.lastname: Kidder
mesh_terms: D000255:Adenosine Triphosphate / Q000737:chemistry; D000483:Alleles; D017398:Alternative Splicing; D000595:Amino Acid Sequence; D000818:Animals; D001755:Blastocyst / Q000378:metabolism; D015153:Blotting, Western; D001835:Body Weight; D017931:DNA Primers / Q000737:chemistry; D004622:Embryo, Mammalian / Q000378:metabolism; D005091:Exons; D005260:Female; D005838:Genotype; D006358:Hot Temperature; D007668:Kidney / Q000378:metabolism; D007700:Kinetics; D008274:Magnesium / Q000652:urine; D008297:Male; D051379:Mice; D008822:Mice, Transgenic; D008856:Microscopy, Fluorescence; D008957:Models, Genetic; D008969:Molecular Sequence Data; D009154:Mutation; D011188:Potassium / Q000737:chemistry / Q000652:urine; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D012964:Sodium / Q000737:chemistry / Q000378:metabolism* / Q000652:urine; D000254:Sodium-Potassium-Exchanging ATPase / Q000235:genetics* / Q000502:physiology*; D013696:Temperature; D019076:Transgenes; D001616:beta-Galactosidase / Q000378:metabolism
chemical_list: D017931:DNA Primers; D000255:Adenosine Triphosphate; D012964:Sodium; D001616:beta-Galactosidase; C498816:Fxyd2 protein, mouse; D000254:Sodium-Potassium-Exchanging ATPase; D008274:Magnesium; D011188:Potassium