Molecular mechanism of N-terminal acetylation by the ternary NatC complex

Abstract

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 specificity profile that overlaps with NatE. Here, we report the Cryo-EM structure of S. pombe NatC with a NatE/C-type bisubstrate analogue 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.

Charting the N-Terminal Acetylome: A Comprehensive Map of Human NatA Substrates

“…These NATs vary greatly in their (subunit) composition and substrate specificities. For the vast majority of identified NATs, structural and biochemical characterizations are at hand, thereby providing molecular insights into their mechanisms of action and modes of regulation besides revealing molecular determinants steering the by and large unique substrate-specific activity potential of NATs (reviewed in [ 4 ] and reported recently for NatC [ 6 ]). While only a partial redundancy in the specificity profiles of certain NATs could be observed, the targeted protein N-termini per NAT appear by and large unique, with only some exceptions as recently proven for the yeast Lge1 protein representing the first redundant yeast NatA/NatD substrate identified to date [ 7 ]…”