title: Role of phylogenetically conserved amino acids in folding of Na,K-ATPase.
abstract: This paper focuses on the amino acid sequence 708-TGDGVNDSPALKK in pig kidney Na,K-ATPase as one of the best conserved among P-type ATPases. In Ca-ATPase this sequence forms a strand-loop-helix structure as part of a Rossman fold next to the phosphorylation site. Substitution of polar residues in the investigated sequence interfered with high-level accumulation of mutant protein. Mutant alpha1-subunit protein only accumulated in membranes from yeast cells grown at 15 degrees C whereas wild-type protein accumulated at both 15 and 35 degrees C. A systematic screen for the molecular mechanism behind lack of accumulation of mutant protein at 35 degrees C showed that transcription and translation were unaffected by the mutations. To demonstrate in vivo protein folding problems, an unfolded protein response reporter system was constructed in yeast. In this strain, only expression of mutant Na,K-ATPase alpha1-subunit caused induction of the unfolded protein response at 35 degrees C, indicating folding problems in the ER. Lowering the expression temperature to 15 degrees C prevented induction of the unfolded protein response after mutant protein expression, indicating correct folding at this temperature. At the permissive temperature mutant proteins were able to escape the endoplasmic reticulum quality control, reach the plasma membrane, and bind ouabain with high affinity. Since mutants in the 708-TGDGVNDSPALKK segment had a thermo inactivation profile identical to that of wild type, they were classified as temperature-sensitive synthesis mutants. The results indicate that this segment contributes side chains of importance for overall folding and maturation of Na,K-ATPase and all other P-type ATPases.
authors.affiliation: Biomembrane Research Centre, August Krogh Institute, University of Copenhagen, Universitetsparken 13, DK-2100 Copenhagen OE, Denmark.
authors.forename: J R
authors.initials: JR
authors.lastname: Jørgensen
authors.forename: P A
authors.initials: PA
authors.lastname: Pedersen
mesh_terms: D000409:Alanine / Q000235:genetics; D019943:Amino Acid Substitution / Q000235:genetics; D000596:Amino Acids / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D001216:Asparagine / Q000235:genetics; D002462:Cell Membrane / Q000235:genetics / Q000378:metabolism; D017124:Conserved Sequence; D004721:Endoplasmic Reticulum / Q000201:enzymology / Q000235:genetics; D004789:Enzyme Activation / Q000235:genetics; D015966:Gene Expression Regulation, Fungal; D008239:Lysine / Q000235:genetics; D016297:Mutagenesis, Site-Directed; D010446:Peptide Fragments / Q000235:genetics / Q000378:metabolism; D010802:Phylogeny; D017510:Protein Folding; D012333:RNA, Messenger / Q000378:metabolism; D011994:Recombinant Proteins / Q000037:antagonists & inhibitors / Q000096:biosynthesis; D012441:Saccharomyces cerevisiae / Q000201:enzymology / Q000235:genetics; D012694:Serine / Q000235:genetics; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D013552:Swine; D013696:Temperature; D013912:Threonine / Q000235:genetics
chemical_list: D000596:Amino Acids; D010446:Peptide Fragments; D012333:RNA, Messenger; D011994:Recombinant Proteins; D013912:Threonine; D012694:Serine; D001216:Asparagine; D000254:Sodium-Potassium-Exchanging ATPase; D008239:Lysine; D000409:Alanine