Dual lysine and N‐terminal acetyltransferases reveal the complexity underpinning protein acetylation

Protein acetylation is a highly frequent protein modification. However, comparatively little is known about its enzymatic machinery. N‐α‐acetylation ( NTA ) and ε‐lysine acetylation ( KA ) are known to be catalyzed by distinct families of enzymes ( NAT s and KAT s, respectively), although the possibility that the same GCN 5‐related N ‐acetyltransferase ( GNAT ) can perform both functions has been debated. Here, we discovered a new family of plastid‐localized GNAT s, which possess a dual specificity. All characterized GNAT family members display a number of unique features. Quantitative mass spectrometry analyses revealed that these enzymes exhibit both distinct KA and relaxed NTA specificities. Furthermore, inactivation of GNAT 2 leads to significant NTA or KA decreases of several plastid proteins, while proteins of other compartments were unaffected. The data indicate that these enzymes have specific protein targets and likely display partly redundant selectivity, increasing the robustness of the acetylation process in vivo . In summary, this study revealed a new layer of complexity in the machinery controlling this prevalent modification and suggests that other eukaryotic GNAT s may also possess these previously underappreciated broader enzymatic activities.