Human Naa50 Protein Displays Broad Substrate Specificity for Amino-terminal Acetylation

Abstract

Amino-terminal acetylation is a critical co-translational modification of the newly synthesized proteins in a eukaryotic cell carried out by six amino-terminal acetyltransferases (NATs). All NATs contain at least one catalytic subunit, and some contain one or two additional auxiliary subunits. For example, NatE is a complex of Naa10, Naa50, and Naa15 (auxiliary). In the present study, the crystal structure of human Naa50 suggested the presence of CoA and acetylated tetrapeptide (AcMMXX) that have co-purified with the protein. Biochemical and thermal stability studies on the tetrapeptide library with variations in the first and second positions confirm our results from the crystal structure that a peptide with Met-Met in the first two positions is the best substrate for this enzyme. In addition, Naa50 acetylated all MXAA peptides except for MPAA. Transcriptome analysis of 10 genes that make up six NATs in humans from eight different cell lines suggests that components of NatE are transcribed in all cell lines, whereas others are variable. Because Naa10 is reported to acetylate all amino termini that are devoid of methionine and Naa50 acetylates all other peptides that are followed by methionine, we believe that NatE complex can be a major contributor for amino-terminal acetylation at the ribosome exit tunnel.Co-translational protein modifications are important biochemical events. Prominent among them are amino-terminal modifications such as methionine cleavage, acetylation, and myristoylation (1-3). Initiator methionine in eukaryotic proteins is removed co-translationally by the enzyme methionine aminopeptidase (MetAP) 3 when the second amino acid is small and uncharged (1). About 70% of the matured proteins do not retain their amino-terminal methionine (4). Similarly, about 90% of all newly synthesized cytosolic proteins undergo aminoterminal acetylation (5). Protein amino-terminal acetylation is carried out by six amino-terminal acetyltransferases (NATs) named sequentially NatA to NatF, classified based on substrate preference (6 -8). NatA acetylates the peptides with serine, alanine, threonine, cysteine, and valine on the amino termini that are formed after MetAP action at the ribosome exit tunnel (5, 9), whereas NatB acts on methionine followed by acidic residues in the second position (10, 11). NatC, NatE, and NatF act on methionine that is followed by hydrophobic amino acids like leucine, phenylalanine, isoleucine, and tryptophan (8, 10, 12, 13). Additionally, NatF also acetylates methionine that is followed specifically by a lysine (14). NatD acetylates the amino termini of Ser-Gly of histones H2A and H4 (15). Each of the NATs (NatA-NatF) is a complex of one or two of the enzymes labeled serially as Naa10, Naa20, Naa30, Naa40, Naa50, and Naa60 attached to one or two of the auxiliary proteins named Naa15, Naa25, Naa35, and Naa38 (7, 9). Some NATs are known to bind to the ribosome at the exit tunnel through their auxiliary subunits (11, 16). Protein amino-terminal acetylation has potential effects on cell ...

NAA50 Is an Enzymatically Active Nα-Acetyltransferase That Is Crucial for Development and Regulation of Stress Responses

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Structural basis of HypK regulating N-terminal acetylation by the NatA complex

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Loss of the Acetyltransferase NAA50 Induces Endoplasmic Reticulum Stress and Immune Responses and Suppresses Growth

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