Protein N-terminal acetylation is predominantly a ribosome-associated modification, with NatA-E serving as the major enzymes. NatC is the most unusual of these enzymes, containing one Naa30 catalytic subunit and two auxiliary subunits, Naa35 and Naa38; and substrate selectivity profile that overlaps with NatE. Here, we report the cryoelectron microscopy structure of S. pombe NatC with a NatE/C-type bisubstrate analog and inositol hexaphosphate (IP₆), and associated biochemistry studies. We find that the presence of three subunits is a prerequisite for normal NatC acetylation activity in yeast and that IP₆ binds tightly to NatC to stabilize the complex. We also describe the molecular basis for IP₆-mediated NatC complex stabilization and the overlapping yet distinct substrate profiles of NatC and NatE.

蛋白质 N 端乙酰化主要是与核糖体相关的修饰，其中 NatA-E 是主要的酶。NatC 是这些酶中最不寻常的，包含一个 Naa30 催化亚基和两个辅助亚基 Naa35 和 Naa38；和与 NatE 重叠的底物选择性分布。在这里，我们报告了具有 NatE/C 型双底物类似物和肌醇六磷酸 (IP _{6 ) 的}S. pombe NatC的低温电子显微镜结构，以及相关的生物化学研究。我们发现三个亚基的存在是酵母中正常 NatC 乙酰化活性的先决条件，并且 IP ₆与 NatC 紧密结合以稳定复合物。_{我们还描述了 IP 6}的分子基础-介导的 NatC 复合物稳定性和 NatC 和 NatE 的重叠但不同的底物谱。