NAA35

NAA35 is the large auxiliary subunit of the NatC N-terminal acetyltransferase complex (NAA30-NAA35-NAA38), which co-translationally acetylates the N-termini of cytoplasmic proteins bearing a bulky hydrophobic or amphipathic residue after the initiator methionine (PMID:12890471, PMID:29247799). Cryo-EM structures of the complex show that all three subunits are required for normal NatC activity and that inositol hexaphosphate (IP6) binds tightly to stabilize the assembly (PMID:34019809); within this architecture, the smaller auxiliary subunit NAA38 orders an N-terminal segment of NAA35 and reorients the NAA30 peptide-binding loop to broaden substrate specificity and increase thermostability (PMID:36638802). NAA35 is functionally indispensable for catalysis: human NAA30 restores NatC-dependent substrate acetylation in yeast only when a Naa35 orthologue is co-expressed, reflecting tight co-evolution of the catalytic and auxiliary subunits (PMID:27555049). Beyond its core acetyltransferase role, NAA35 is induced through the ATF6 branch of the unfolded protein response in muscle and drives cancer-cachexia muscle wasting: its knockdown lowers cathepsin K, preserves insulin receptor substrate 1 and downstream AKT/S6K signaling, suppresses the atrophy genes MuRF1 and MAFbx1, and restores muscle mass (PMID:41852114).

1. 1987 Medium

   Before its enzymatic identity was known, the yeast orthologue Mak10 was found to be required for the structural stability of L-A double-stranded RNA virus-like particles, providing the first functional handle on the gene.

   Evidence In vitro RNA polymerase and particle stability assays on CsCl gradients with temperature-sensitive mutants in yeast

   PMID:3550421

   Open questions at the time

   • No molecular mechanism linking Mak10 to particle stability
   • No connection yet to acetyltransferase activity
2. 1992 Medium

   Cloning of MAK10 defined it as an essential single gene whose loss destabilizes L-A replication and impairs growth on non-fermentable carbon sources, establishing pleiotropic cellular roles and glucose-repressed regulation.

   Evidence Gene cloning, lacZ reporter fusions, deletion and point-mutant genetics, and growth assays in yeast

   PMID:1398065

   Open questions at the time

   • Biochemical activity of the encoded protein not yet defined
   • Relationship between L-A and carbon-source phenotypes unresolved
3. 2003 Medium

   The gene was reassigned as an auxiliary subunit of the NatC N-terminal acetyltransferase complex, explaining its activity as part of a Met-X(bulky hydrophobic) substrate-acetylating machine.

   Evidence Biochemical complex composition and enzymatic activity characterization in yeast

   PMID:12890471

   Open questions at the time

   • Catalytic contribution of the auxiliary subunit versus Mak3 not separated
   • Human complex not yet characterized
4. 2016 Medium

   Cross-species complementation showed human NAA35 is required for human NatC catalytic activity in vivo and co-evolves with its catalytic partner NAA30.

   Evidence Yeast complementation using Arl3-Golgi localization readout with human/yeast subunit co-expression

   PMID:27555049

   Open questions at the time

   • Direct structural basis of the subunit interdependence not shown
   • No in vitro reconstitution of the human complex
5. 2017 Medium

   The human NatC complex (NAA30-NAA35-NAA38) was reconstituted and shown to acetylate a classical NatC substrate peptide in vitro, confirming subunit composition and substrate logic in human cells.

   Evidence In vitro acetyltransferase activity assay and subcellular imaging

   PMID:29247799

   Open questions at the time

   • Quantitative contribution of each subunit to catalysis not resolved
   • Substrate repertoire beyond model peptides undefined
6. 2021 High

   A cryo-EM structure of the NatC complex with a bisubstrate analog and IP6 established the structural requirement for all three subunits and revealed IP6 as a complex-stabilizing cofactor.

   Evidence Cryo-EM structure determination, biochemical activity assays, and IP6 binding studies in S. pombe NatC

   PMID:34019809

   Open questions at the time

   • Species-specific differences in cofactor engagement not yet addressed
   • Functional consequences of IP6 in cells not tested
7. 2023 High

   Human NatC cryo-EM structures defined the mechanistic role of NAA38 in ordering an NAA35 N-terminal segment and reorienting the NAA30 peptide-binding loop, accounting for thermostability and broadened substrate specificity.

   Evidence Cryo-EM structures with and without NAA38 plus thermostability and substrate-specificity assays of human NatC

   PMID:36638802

   Open questions at the time

   • Catalytic mechanism of acetyl transfer not fully kinetically dissected
   • In-cell substrate consequences of NAA38-dependent specificity not mapped
8. 2026 Medium

   NAA35 was identified as a UPR-induced mediator of muscle wasting, connecting its acetyltransferase-complex role to a disease pathway in cancer cachexia via cathepsin K and IRS1/AKT signaling.

   Evidence Genome-wide CRISPR screen, in vivo shRNA knockdown in tumor-bearing mice, ATF6 pharmacology, western blotting, and muscle function assays

   PMID:41852114

   Open questions at the time

   • Whether NatC acetyltransferase activity per se drives CTSK regulation not established
   • Direct NAA35 substrates in the cachexia pathway unidentified

• The specific substrate repertoire of NAA35-containing NatC in human physiology and how its acetyltransferase function connects mechanistically to its disease and reproductive phenotypes remain open.
• No catalog of endogenous NatC substrates tied to specific phenotypes
• Causal link between acetylation activity and cachexia/reproduction phenotypes untested