Abstract

N-terminal acetylation (Nt-acetylation) catalyzed by conserved N-terminal acetyltransferases or NATs embodies a modification with one of the highest stoichiometries reported for eukaryotic protein modifications to date. Comprising the catalytic N-alpha acetyltransferase (NAA) subunit NAA10 plus the ribosome anchoring regulatory subunit NAA15, NatA represents the major acetyltransferase complex with up to 50% of all mammalian proteins representing potential substrates. Largely in consequence of the essential nature of NatA and its high enzymatic activity, its experimentally confirmed mammalian substrate repertoire remained poorly charted. In this study, human NatA knockdown conditions achieving near complete depletion of NAA10 and NAA15 expression resulted in lowered Nt-acetylation of over 25% out of all putative NatA targets identified, representing an up to 10-fold increase in the reported number of substrate N-termini affected upon human NatA perturbation. Besides pointing to less efficient NatA substrates being prime targets, several putative NatE substrates were shown to be affected upon human NatA knockdown. Intriguingly, next to a lowered expression of ribosomal proteins and proteins constituting the eukaryotic 48S preinitiation complex, steady-state levels of protein N-termini additionally point to NatA Nt-acetylation deficiency directly impacting protein stability of knockdown affected targets.

Highlights

  • Clemente Capasso andCo- and post-translational protein N-terminal acetylation (Nt-acetylation or NTA)exemplifies an omnipresent and abundant protein modification with one of the highest stoichiometries in mammalian cells reported for protein modifications to date [1,2].NTA contributes to an increase in mammalian N-terminal proteoform diversity by the occurrence of partially NTA protein N-termini [3]

  • We report on improved human NatA knockdown conditions achieving a significant depletion of NAA10 and NAA15 expression

  • We characterized the in-vivo substrate specificity of the human NatA complex by comparing the Nt-acetylomes of A-431 cells treated with siNAA10/siNAA15 pool

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Summary

Introduction

Clemente Capasso andCo- and post-translational protein N-terminal acetylation (Nt-acetylation or NTA)exemplifies an omnipresent and abundant protein modification with one of the highest stoichiometries in mammalian cells reported for protein modifications to date [1,2].NTA contributes to an increase in mammalian N-terminal proteoform diversity by the occurrence of partially NTA protein N-termini [3]. 12 NATs—including 8 distinct eukaryotic NATs NatA to NatH next to 1 archaeal and 3 bacterial NATs—with evolutionary conserved folds and related catalytic mechanisms have been identified [4,5]. These NATs vary greatly in their (subunit) composition and substrate specificities. 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 Lge protein representing the first redundant yeast NatA/NatD substrate identified to date [7]

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