Functional Insights Into Protein Acetylation in the Hyperthermophilic Archaeon Sulfolobus islandicus

About 26% of the total proteins and 44% of the identified proteins were acetylated at lysine residues and the N terminus, respectively, in the hyperthermophilic archaeon Sulfolobus islandicus. A Pat homolog preferentially acetylated a group of acyl-CoA synthetases among the acetylated proteins, whereas an Ard1 homolog exhibited broad substrate specificity. A S. islandicus mutant strain lacking the Pat homolog showed no significant growth defects and that lacking the Ard1 homolog grew more slowly than the parent strain. Proteins undergo acetylation at the N epsilon-amino group of lysine residues and the N alpha-amino group of the N terminus in Archaea as in Bacteria and Eukarya. However, the extent, pattern and roles of the modifications in Archaea remain poorly understood. Here we report the proteomic analyses of a wild-type Sulfolobus islandicus strain and its mutant derivative strains lacking either a homolog of the protein acetyltransferase Pat (Delta SisPat) or a homolog of the Nt-acetyltransferase Ard1 (Delta SisArd1). A total of 1708 N epsilon-acetylated lysine residues in 684 proteins (26% of the total proteins), and 158 Nt-acetylated proteins (44% of the identified proteins) were found in S. islandicus. Delta SisArd1 grew more slowly than the parental strain, whereas Delta SisPat showed no significant growth defects. Only 24 out of the 1503 quantifiable N epsilon-acetylated lysine residues were differentially acetylated, and all but one of the 24 residues were less acetylated by >1.3 fold in Delta SisPat than in the parental strain, indicating the narrow substrate specificity of the enzyme. Six acyl-CoA synthetases were the preferred substrates of SisPat in vivo, suggesting that N epsilon-acetylation by the acetyltransferase is involved in maintaining metabolic balance in the cell. Acetylation of acyl-CoA synthetases by SisPat occurred at a sequence motif conserved among all three domains of life. On the other hand, 92% of the acetylated N termini identified were acetylated by SisArd1 in the cell. The enzyme exhibited broad substrate specificity and could modify nearly all types of the target N termini of human NatA-NatF. The deletion of the SisArd1 gene altered the cellular levels of 18% of the quantifiable proteins (1518) by >1.5 fold. Consistent with the growth phenotype of Delta SisArd1, the cellular levels of proteins involved in cell division and cell cycle control, DNA replication, and purine synthesis were significantly lowered in the mutant than those in the parental strain.