Hypusine


Hypusine is an unusual amino acid found in all eukaryotes and in some archaea, but not in bacteria. The only known protein containing hypusine is eukaryotic translation initiation factor 5A and a similar protein found in archaebacteria. In humans, two isoforms of eIF-5A have been described: eIF5A-1 and eIF5A-2. They are encoded by two different genes EIF5A and EIF5A2. The protein is involved in protein biosynthesis and promotes the formation of the first peptide bond. The region surrounding the hypusine residue is highly conserved and is essential to the function of eIF5A. Thus, hypusine and eIF-5A appear to be vital for the viability and proliferation of eukaryotic cells.
Hypusine is formed in eIF-5A by post-translational modification of one of the lysyl residues. There are two reactions and two enzymes involved:
An excess of hypusine was found in the urine of children and patients with familial hyperlysinemia.
Hypusine was first isolated from bovine brain by Japanese scientists Shiba et al. in 1971. The name hypusine indicates that the molecule comprises moieties of hydroxyputrescine and lysine.