Docking the mitochondrial inhibitor protein IF₁ to a membrane receptor different from the F₁‐ATPase β subunit

Abstract

Monoclonal antibodies reacting with the inhibitor protein (IF1) of the mitochondrial ATPase/ATP synthase complex did not modify the IF1‐induced inhibition of soluble F1 ATPase activity. On the contrary, they increased the ATPase activity of inverted electron‐transport particles without inducing a significant release of IF1 from these particles. This suggested that IF1 could be linked to a membrane protein when it was not inhibiting the ATPase activity. IF1 antibodies have been used to show that IF1 can bind not only to the β subunit of F1‐ATPase [Klein, G., Satre, M., Dianoux, A. C. & Vignais, P. V. (1981) Biochemistry 20, 1339–1344] but also to a protein present in the inner‐mitochondrial membrane. The cross‐linking of IF1 to this membrane protein gave a product of Mr 15000–16000 that migrated differently from IF1 and from the dimer of IF1 using SDS/PAGE. When the cross‐linked product was obtained by using a cleavable cross‐linking reagent, the complex between IF1 and the docking protein was partly dissociated and free IF1 was recovered. Considering the molecular mass of IF1, this docking protein for IF1 has apparent Mr 5000–6000. The complex between IF1 and this receptor protein can be detected in low amounts by antibodies against IF1 in the absence of cross‐linking reagent. Since this complex remained in the pellet after treatment of the membrane with Triton X‐100, it should be a membrane protein. Therefore, IF1 can bind not only to its inhibitory‐binding site at the β subunit of F1, but also to a non inhibitory site which is a membrane protein of approximate Mr 5000–6000.

Impaired ATP Synthase Assembly Associated with a Mutation in the Human ATP Synthase Subunit 6 Gene

“…Nevertheless, the effects of the mutation must necessarily be subtle, 3 N. Hance and I. J. Holt, unpublished data. (37), yet this complex is considerably larger than 100 kDa and therefore likely involves at least one other protein, perhaps the 21-kDa protein partly characterized previously (38) . FIG.…”

Loss of Function of Cytochrome c in Jurkat Cells Undergoing Fas-mediated Apoptosis

“…Such a proteolytic alteration could be accomplished by one of the death proteases or by another protease released through the action of a death protease. As to inhibitors, a precedent exists in the form of IF1, a small mitochondrial polypeptide that inhibits the ATPase activity of Complex V when the potential across the inner mitochondrial membrane is low (27)(28)(29)(30)(31)(32)(33)(34). This regulatory polypeptide prevents the destruction of ATP that would otherwise occur if for some reason the mitochondrial transmem- brane potential should transiently collapse (28).…”

The Inhibitor Protein (IF1) of the F1F0-ATPase Modulates Human Osteosarcoma Cell Bioenergetics

“…First, it has been reported that besides binding the ␤ subunit of F 1 , IF 1 can bind another protein of low M r of the inner mitochondrial membrane (47) and this might lead to ⌬ m enhancement in respiring mitochondria. This hypothesis does not seem acceptable because native PAGE analysis in our hand never showed the inhibitor protein in bands other than the IF 1 -ATP synthase complexes (Fig.…”