N-terminal acetylation shields proteins from degradation and promotes age-dependent motility and longevity

Abstract

Most eukaryotic proteins are N-terminally acetylated, but the functional impact on a global scale has remained obscure. Using genome-wide CRISPR knockout screens in human cells, we reveal a strong genetic dependency between a major N-terminal acetyltransferase and specific ubiquitin ligases. Biochemical analyses uncover that both the ubiquitin ligase complex UBR4-KCMF1 and the acetyltransferase NatC recognize proteins bearing an unacetylated N-terminal methionine followed by a hydrophobic residue. NatC KO-induced protein degradation and phenotypes are reversed by UBR knockdown, demonstrating the central cellular role of this interplay. We reveal that loss of Drosophila NatC is associated with male sterility, reduced longevity, and age-dependent loss of motility due to developmental muscle defects. Remarkably, muscle-specific overexpression of UbcE2M, one of the proteins targeted for NatC KO-mediated degradation, suppresses defects of NatC deletion. In conclusion, NatC-mediated N-terminal acetylation acts as a protective mechanism against protein degradation, which is relevant for increased longevity and motility.

A nonsense variant in the N‐terminal acetyltransferase NAA30 may be associated with global developmental delay and tracheal cleft

“…Another possibility is that a truncated NAA30-Q82* protein can act in a dominant negative manner causing a more dramatic reduction in NatC-mediated Nt-acetylation or have toxic effect(s) independently of protein Nt-acetylation. Furthermore, deletion of NAA35 or NAA38 in haploid HAP1 cells reduces NAA30 protein levels, and similar NatC interdependence has been observed in yeast (Drazic & Varland, 2021;Varland et al, 2022).…”

“…Considering the ubiquitous nature of the NatC complex, understanding how potential NAA30 variants cause disease requires prolonged effort. In a recent study, we found that human NatC plays a protective role in proteostasis by shielding proteins with hydrophobic N-termini from proteasomal degradation by the ubiquitin ligase UBR4 (Varland et al, 2022). A well-known target of NatC is the NEDD8-conjugating (E2) enzyme UBE2M.…”

“…Loss of NatC activity leads to a significant reduction in UBE2M protein levels, decreased cullin neddylation and proteostasis defects (Varland et al, 2022). The cullins regulate diverse biological processes, and their dysfunction is implicated in human diseases (Cui et al, 2016;Hammill et al, 2018;Lu & Pfeffer, 2014;Petroski & Deshaies, 2005).…”

“…Human NatC activity has been linked to mitochondrial and Golgi integrity (Starheim et al, 2017; Van Damme et al, 2016), apoptosis (Starheim et al, 2009) and glutathione metabolism (Cao et al, 2019) as well as cancer cell survival and progression (Mughal et al, 2015; Varland, Myklebust, et al, 2018). The most important role of human NatC‐mediated Nt‐acetylation may be to protect proteins against UBR4‐KCMF1‐mediated protein degradation (Varland et al, 2022). Organismal studies have further highlighted the physiological importance of NatC‐mediated Nt‐acetylation.…”

“…In the roundworm, Caenorhabditis elegans NatC is required for normal animal development, stress responses, and entry into a stress‐induced developmental stage (Malinow et al, 2022; Warnhoff et al, 2014). Finally, NatC activity is important for age‐dependent motility and longevity in the fruit fly Drosophila melanogaster (Varland et al, 2022).…”