title: Importance of stalk segment S5 for intramolecular communication in the sarcoplasmic reticulum Ca2+-ATPase.
abstract: Sixteen residues in stalk segment S5 of the Ca(2+)-ATPase of sarcoplasmic reticulum were studied by site-directed mutagenesis. The rate of the Ca(2+) binding transition, determined at 0 degrees C, was enhanced relative to wild type in mutants Ile(743) --> Ala, Val(747) --> Ala, Glu(748) --> Ala, Glu(749) --> Ala, Met(757) --> Gly, and Gln(759) --> Ala and reduced in mutants Asp(737) --> Ala, Asp(738) --> Ala, Ala(752) --> Leu, and Tyr(754) --> Ala. In mutant Arg(762) --> Ile, the rate of the Ca(2+) binding transition was wild type like at 0 degrees C, whereas it was 3.5-fold reduced relative to wild type at 25 degrees C. The rate of dephosphorylation of the ADP-insensitive phosphoenzyme was increased conspicuously in mutants Ile(743) --> Ala and Tyr(754) --> Ala (close to 20-fold in the absence of K(+)) and increased to a lesser extent in Asn(739) --> Ala, Glu(749) --> Ala, Gly(750) --> Ala, Ala(752) --> Gly, Met(757) --> Gly, and Arg(762) --> Ile, whereas it was reduced in mutants Asp(737) --> Ala, Val(744) --> Gly, Val(744) --> Ala, Val(747) --> Ala, and Ala(752) --> Leu. In mutants Ile(743) --> Ala, Tyr(754) --> Ala, and Arg(762) --> Ile, the apparent affinities for vanadate were enhanced 23-, 30-, and 18-fold, respectively, relative to wild type. The rate of Ca(2+) dissociation was 11-fold increased in Gly(750) --> Ala and 2-fold reduced in Val(747) --> Ala. Mutants with alterations to Arg(751) either were not expressed at a significant level or were completely nonfunctional. The findings show that S5 plays a crucial role in mediating communication between the Ca(2+) binding pocket and the catalytic domain and that Arg(751) is important for both structural and functional integrity of the enzyme.
authors.affiliation: Department of Physiology, University of Aarhus, DK-8000 Aarhus C, Denmark.
authors.forename: T L
authors.initials: TL
authors.lastname: Sorensen
authors.forename: J P
authors.initials: JP
authors.lastname: Andersen
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D001665:Binding Sites; D019556:COS Cells; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D000252:Calcium-Transporting ATPases / Q000737:chemistry* / Q000378:metabolism; D020134:Catalytic Domain; D010766:Phosphorylation; D012519:Sarcoplasmic Reticulum / Q000201:enzymology*; D013329:Structure-Activity Relationship; D013696:Temperature; D014638:Vanadates / Q000494:pharmacology
chemical_list: D000001:Calcimycin; D014638:Vanadates; D000255:Adenosine Triphosphate; D000252:Calcium-Transporting ATPases; D002118:Calcium