Intersubunit bridging by Na+ ions as a rationale for the unusual stability of the c-rings of Na+-translocating F1F0 ATP synthases.
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.
Meier
Thomas
T
Institut für Mikrobiologie, Eidgenössische Technische Hochschule, ETH-Zentrum, CH-8092 Zürich, Switzerland.
Dimroth
Peter
P
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*
D001426:Bacterial Proteins; D021122:Protein Subunits; D008094:Lithium; D012964:Sodium; D006180:Proton-Translocating ATPases