| ATP5A (ATP5F1A), also known as ATP synthase F1 subunit α, is a nuclear‑encoded, mitochondrially localized subunit of complex V that forms part of the catalytic F1 head of the ATP synthase holoenzyme and is essential for oxidative phosphorylation‑driven ATP synthesis, acting both as a structural scaffold for the β catalytic subunits and as a regulatory element that coordinates nucleotide binding and release during rotary catalysis. The F1 portion of mitochondrial ATP synthase comprises three α and three β subunits arranged alternately around the central γ shaft together with δ and ε subunits, and primary structure and stoichiometry studies of bovine F1 showed that the α subunit is weakly homologous to β, resides at the noncatalytic nucleotide‑binding sites and contributes to conformational coupling between β active sites and the rotary stalk; more recent structural modeling of human ATP5F1A variants confirms that the α subunit presents a β‑interacting surface adjacent to the β catalytic site whose charge distribution and geometry are critical for complex stability and function. During oxidative phosphorylation, proton motive force generated by the electron transport chain drives rotation of the Fo c‑ring and central stalk, while the α3β3 hexamer undergoes sequential conformational changes that alternately bind ADP and inorganic phosphate, catalyze ATP formation and release product, and ATP5F1A participates by binding noncatalytic nucleotides and transmitting mechanical energy to β subunits, with defects in α–β interactions impairing rotary coupling and ATP output. Pathogenic ATP5F1A variants illustrate the functional importance of this interface: a recurrent de novo Arg207His substitution creates an abnormal region of negative charge on the β‑interacting surface of α, adjacent to the β active site, leading to complex V assembly defects, reduced ATP synthesis, neonatal hyperlactatemia and hyperammonemia, and a remitting clinical course with apparent resolution of symptoms by 18 months, while other dominant‑negative missense variants cause persistent developmental delay, neuro‑motor impairments and biochemical complex V deficiency, demonstrating that subtle changes in ATP5F1A structure can produce a spectrum of mitochondrial encephalopathies. Earlier work on a complex V ATP5A1 defect in two siblings with fatal neonatal mitochondrial encephalopathy showed that a heterozygous ATP5A1 mutation combined with silencing of the maternal allele reduced ATP5A1 expression to about half of normal, destabilized the α–β interaction, decreased complex V content and activity, and that complementation with wild‑type ATP5A1 restored complex V function in patient fibroblasts, confirming that ATP5A is indispensable for holoenzyme stability and that dosage effects can be sufficient to cause severe disease. Beyond its canonical bioenergetic role, ATP5A1 has been implicated in transcriptional and post‑transcriptional regulation in cancer cells, where aberrant expression and alternative splicing of ATP5A1 correlate with changes in oncogene regulation and tumor progression, and ATP synthase modulation by small molecules such as Mitochonic Acid 5, which facilitates ATP synthase oligomerization and improves survival in mitochondrial disease models, underscores the therapeutic relevance of targeting ATP5A‑containing complexes in disorders of energy metabolism. Recent preprint work indicates that specific cytosolic RNAs can bind ATP5A1 precursor proteins at the outer mitochondrial surface and promote their import, adding a riboregulatory layer to ATP5A biogenesis and suggesting that dysregulation of RNA‑mediated import may contribute to complex V deficiencies. |
