title: Intersubunit bridging by Na+ ions as a rationale for the unusual stability of the c-rings of Na+-translocating F1F0 ATP synthases.
abstract: The oligomeric c-rings of Na+-translocating F1F0 ATP synthases exhibit unusual stability, resisting even boiling in SDS. Here, we show that the molecular basis for this remarkable property is intersubunit crossbridging by Na+ or Li+ ions. The heat stability of c11 was dependent on the presence of Na+ or Li+ ions. For equal stability, 10 times higher Li+ than Na+ concentrations were required, reflecting the 10 times lower binding affinity for Li+ than for Na+. In a recent structural model of c11, the Na+ or Li+ binding ligands are located on neighboring c-subunits, which thus become crossbridged by the binding of either alkali ion with a concomitant increase in the stability of the ring. Site-directed mutagenesis strengthens the essential role of glutamate 65 in the crossbridging of the subunits and also corroborates the proposed stabilizing effect of an ion bridge including aspartate 2.
authors.affiliation: Institut für Mikrobiologie, Eidgenössische Technische Hochschule, ETH-Zentrum, CH-8092 Zürich, Switzerland.
authors.forename: Thomas
authors.initials: T
authors.lastname: Meier
authors.forename: Peter
authors.initials: P
authors.lastname: Dimroth
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D008094:Lithium / Q000378:metabolism*; D008958:Models, Molecular; D009154:Mutation; D021122:Protein Subunits / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D006180:Proton-Translocating ATPases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D021122:Protein Subunits; D008094:Lithium; D012964:Sodium; D006180:Proton-Translocating ATPases