Hypusine is an uncommon

amino acid Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although hundreds of amino acids exist in nature, by far the most important are the alpha-amino acids, which comprise proteins. Only 22 alpha a ...

found in all eukaryotes and in some archaea, but not in

bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of prokaryotic microorganisms. Typically a few micrometr ...

. The only known proteins containing the hypusine residue is eukaryotic translation initiation factor 5A (eIF-5A) and a similar protein found in archaea. In humans, two isoforms of eIF-5A have been described: eIF5A-1 and eIF5A-2. They are encoded by two distinct genes

EIF5A Eukaryotic translation initiation factor 5A-1 is a protein that in humans is encoded by the ''EIF5A'' gene. It is the only known protein to contain the unusual amino acid hypusine 'N''ε-(4-amino-2-hydroxybutyl)-lysine which is synthesized on e ...

and

EIF5A2 Eukaryotic translation initiation factor 5A-2 is a protein that in humans is encoded by the ''EIF5A2'' gene In biology, the word gene (from , ; "...Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." me ...

. 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 Post-translational modification (PTM) is the covalent and generally enzymatic modification of proteins following protein biosynthesis. This process occurs in the endoplasmic reticulum and the golgi apparatus. Proteins are synthesized by ribos ...

of one of the

lysyl Lysine (symbol Lys or K) is an α-amino acid that is a biosynthesis, precursor to many proteins. It contains an α-amino group (which is in the protonation, protonated form under biological conditions), an α-carboxylic acid group (which is in ...

residues. Two reactions and two enzymes are involved: *1. Deoxyhypusine synthase catalyzes the cleavage of the polyamine

spermidine Spermidine is a polyamine compound () found in ribosomes and living tissues and having various metabolic functions within organisms. It was originally isolated from semen. Function Spermidine is an aliphatic polyamine. Spermidine synthase (SP ...

and transfer of its 4-aminobutyl moiety to the ε-amino group of one specific lysine residue of the eIF-5A precursor to form deoxyhypusine and 1,3-diaminopropane. *2. Deoxyhypusine hydroxylase mediates the formation of hypusine by addition of a hydroxyl group to the deoxyhypusine residue. An excess of hypusine was found in the urine of children and patients with familial

hyperlysinemia Hyperlysinemia is an autosomal recessive metabolic disorder characterized by an abnormal increase of lysine in the blood, but appears to be benign. It is caused by mutations in ''AASS'', which encodes α-aminoadipic semialdehyde synthase. Hyper ...

. 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.

References

Amino acids Non-proteinogenic amino acids {{Non-proteinogenic amino acids

See also

References