Crucial aminoacids in the FO sector of the F1FO-ATP synthase address H+ across the inner mitochondrial membrane: molecular implications in mitochondrial dysfunctions

Ca2+ as cofactor of the mitochondrial H+ -translocating F1 FO -ATP(hydrol)ase

The mitochondrial F₁ F_O -ATPase in the presence of the natural cofactor Mg²⁺ acts as the enzyme of life by synthesizing ATP, but it can also hydrolyze ATP to pump H⁺ . Interestingly, Mg²⁺ can be replaced by Ca²⁺ , but only to sustain ATP hydrolysis and not ATP synthesis. When Ca²⁺ inserts in F₁ , the torque generation built by the chemomechanical coupling between F₁ and the rotating central stalk was reported as unable to drive the transmembrane H⁺ flux within F_O . However, the failed H⁺ translocation is not consistent with the oligomycin-sensitivity of the Ca²⁺ -dependent F₁ F_O -ATP(hydrol)ase. New enzyme roles in mitochondrial energy transduction are suggested by recent advances. Accordingly, the structural F₁ F_O -ATPase distortion driven by ATP hydrolysis sustained by Ca²⁺ is consistent with the permeability transition pore signal propagation pathway. The Ca²⁺ -activated F₁ F_O -ATPase, by forming the pore, may contribute to dissipate the transmembrane H⁺ gradient created by the same enzyme complex.

Modulation of OSCP mitigates mitochondrial and synaptic deficits in a mouse model of Alzheimer's pathology

Synaptic failure underlies cognitive impairment in Alzheimer's disease (AD). Cumulative evidence suggests a strong link between mitochondrial dysfunction and synaptic deficits in AD. We previously found that oligomycin-sensitivity-conferring protein (OSCP) dysfunction produces pronounced neuronal mitochondrial defects in AD brains and a mouse model of AD pathology (5xFAD mice). Here, we prevented OSCP dysfunction by overexpressing OSCP in 5xFAD mouse neurons in vivo (Thy-1 OSCP/5xFAD mice). This approach protected OSCP expression and reduced interaction of amyloid-beta (Aβ) with membrane-bound OSCP. OSCP overexpression also alleviated F1Fo ATP synthase deregulation and preserved mitochondrial function. Moreover, OSCP modulation conferred resistance to Aβ-mediated defects in axonal mitochondrial dynamics and motility. Consistent with preserved neuronal mitochondrial function, OSCP overexpression ameliorated synaptic injury in 5xFAD mice as demonstrated by preserved synaptic density, reduced complement-dependent synapse elimination, and improved synaptic transmission, leading to preserved spatial learning and memory. Taken together, our findings show the consequences of OSCP dysfunction in the development of synaptic stress in AD-related conditions and implicate OSCP modulation as a potential therapeutic strategy.

Functional importance of αAsp-350 in the catalytic sites of Escherichia coli ATP synthase

Negatively charged residue αAsp-350 of the highly conserved VISIT-DG sequence is required for Pi binding and maintenance of the phosphate-binding subdomain in the catalytic sites of Escherichia coli F₁F_o ATP synthase. αAsp-350 is situated in close proximity, 2.88 Å and 3.5 Å, to the conserved known phosphate-binding residues αR376 and βR182. αD350 is also in close proximity, 1.3 Å, to another functionally important residue αG351. Mutation of αAsp-350 to Ala, Gln, or Arg resulted in substantial loss of oxidative phosphorylation and reduction in ATPase activity by 6- to 16-fold. The loss of the acidic side chain in the form of αD350A, αD350Q, and αD350R caused loss of Pi binding. While removal of Arg in the form of αR376D resulted in the loss of Pi binding, the addition of Arg in the form of αG351R did not affect Pi binding. Our data demonstrates that αD350R helps in the proper orientation of αR376 and βR182 for Pi binding. Fluoroaluminate, fluoroscandium, and sodium azide caused almost complete inhibition of wild type enzyme and caused variable inhibition of αD350 mutant enzymes. NBD-Cl (4-chloro-7-nitrobenzo-2-oxa-1, 3-diazole) caused complete inhibition of wild type enzyme while some residual activity was left in mutant enzymes. Inhibition characteristics supported the conclusion that NBD-Cl reacts in βE (empty) catalytic sites. Phosphate protected against NBD-Cl inhibition of wild type and αG351R mutant enzymes but not inhibition of αD350A, αD350Q, αD350R, or αR376D mutant enzymes. These results demonstrate that αAsp-350 is an essential residue required for phosphate binding, through its interaction with αR376 and βR182, for normal function of phosphate binding subdomain and for transition state stabilization in ATP synthase catalytic sites.

A Therapeutic Role for the F1FO-ATP Synthase

Recently, the F₁F_O-ATP synthase, due to its dual role of life enzyme as main adenosine triphosphate (ATP) maker and of death enzyme, as ATP dissipator and putative structural component of the mitochondrial permeability transition pore (mPTP), which triggers cell death, has been increasingly considered as a drug target. Accordingly, the enzyme offers new strategies to counteract the increased antibiotic resistance. The challenge is to find or synthesize compounds able to discriminate between prokaryotic and mitochondrial F₁F_O-ATP synthase, exploiting subtle structural differences to kill pathogens without affecting the host. From this perspective, the eukaryotic enzyme could also be made refractory to macrolide antibiotics by chemically produced posttranslational modifications. Moreover, because the mitochondrial F₁F_O-ATPase activity stimulated by Ca²⁺ instead of by the natural modulator Mg²⁺ is most likely involved in mPTP formation, effectors preferentially targeting the Ca²⁺-activated enzyme may modulate the mPTP. If the enzyme involvement in the mPTP is confirmed, Ca²⁺-ATPase inhibitors may counteract conditions featured by an increased mPTP activity, such as neurodegenerative and cardiovascular diseases and physiological aging. Conversely, mPTP opening could be pharmacologically stimulated to selectively kill unwanted cells. On the basis of recent literature and promising lab findings, the action mechanism of F₁ and F_O inhibitors is considered. These molecules may act as enzyme modifiers and constitute new drugs to kill pathogens, improve compromised enzyme functions, and limit the deathly enzyme role in pathologies. The enzyme offers a wide spectrum of therapeutic strategies to fight at the molecular level diseases whose treatment is still insufficient or merely symptomatic.