| ATPase family AAA domain–containing protein 3A (ATAD3A) is a nuclear‑encoded mitochondrial inner membrane protein of the AAA+ ATPase family that forms higher‑order oligomers spanning the inner membrane and contacting the outer membrane, where it functions as a structural and signaling scaffold coordinating mitochondrial DNA organization, cholesterol trafficking, and organelle dynamics. The protein contains an N‑terminal region embedded in the inner membrane, central coiled‑coil and helical segments that mediate self‑association and interaction with other mitochondrial and endoplasmic reticulum proteins, and a C‑terminal cytosol‑facing AAA ATPase domain whose oligomerization and nucleotide binding drive conformational changes essential for its scaffolding and remodeling functions. ATAD3A localizes to inner membrane microdomains that underlie mitochondrial nucleoids and binds mitochondrial DNA, including D‑loop regions, thereby contributing to nucleoid positioning, compaction, and coupling of nucleoids to the inner membrane, which stabilizes mitochondrial DNA replication and transcription machineries and links genome maintenance to membrane architecture. Interaction with components of the mitochondrial translation apparatus and ribosome‑rich inner membrane regions connects ATAD3A to regulation of mitochondrial protein synthesis, and its presence at inner–outer membrane contact sites supports formation of mitochondria–ER contact zones that coordinate lipid and cholesterol transfer and integrate mitochondrial metabolism with ER signaling. ATAD3A participates in cholesterol trafficking toward the inner membrane and steroidogenic pathways, and its positioning within an inner‑membrane network influences distribution of cholesterol and other lipids that shape membrane fluidity, cristae morphology, and function of respiratory chain complexes. The protein also modulates stress signaling at mitochondria–ER junctions by interacting with the PERK kinase and restricting PERK activity locally, which protects mitochondrial protein translation and respiratory capacity during endoplasmic reticulum stress and contributes to integrated mitochondrial stress responses. Pathogenic ATAD3A variants identified in human neuro‑mitochondrial disorders affect domains involved in oligomerization, ATPase function, or membrane anchoring and exhibit loss‑of‑function or dominant‑negative behavior associated with fragmented mitochondrial networks, altered number and size of mitochondria, disorganized cristae, reduced activities of respiratory chain complexes I, IV, and V, and enhanced autophagy and mitophagy. These mitochondrial defects align with clinical phenotypes that include developmental delay, hypotonia, cardiomyopathy, optic atrophy, and cerebellar abnormalities and underscore the requirement of intact ATAD3A scaffolding for neuronal and muscle bioenergetics. Dysregulated ATAD3A expression and signaling are also linked to cancer biology, where altered ATAD3A‑dependent control of mitochondrial dynamics, cholesterol flux, and stress pathways contributes to metabolic adaptation, proliferation, and resistance to cell death. |
