Inactivation of eukaryotic initiation factor 5A (eIF5A) by specific acetylation of its hypusine residue by spermidine/spermine acetyltransferase 1 (SSAT1)

eIF5A (eukaryotic translation initiation factor 5A) is activated by the posttranslational synthesis of hypusine [N ε ‐(4‐amino‐2‐hydroxybutyl)lysine] and the hypusine modification is essential for cell proliferation. In this study, we report selective acetylation of the hypusine and/or deoxyhypusine residue of eIF5A by a key polyamine catabolic enzyme, spermidine/spermine‐ N 1 ‐acetyltransferase 1 (SSAT1). This enzyme normally catalyzes the N 1 ‐acetylation of spermine and spermidine to form acetyl‐derivatives, which in turn are degraded to lower polyamines. Although SSAT1 has been reported to exert other effects in cells by its interaction with other cellular proteins, eIF5A is the first target protein specifically acetylated by SSAT1. Hypusine or deoxyhypusine, as the free amino acid, does not act as a substrate for SSAT1, suggesting a macromolecular interaction between eIF5A and SSAT1. Indeed, the binding of eIF5A and SSAT1 was confirmed by pull‐down assays. The effect of the acetylation of hypusine on eIF5A activity was assessed by comparison of acetylated vs non‐acetylated bovine testis eIF5A in the methionyl‐puromycin synthesis assay. The loss of eIF5A activity by this SSAT1‐mediated acetylation confirms the strict structural requirement for the hypusine side chain and suggests a possible regulation of eIF5A by hypusine acetylation/deacetylation The research was supported by the Intramural Research Program of National Institute of Dental and Craniofacial Research (NIDCR)