title: Synthetic, structural and biological studies of the ubiquitin system: synthesis and crystal structure of an analogue containing unnatural amino acids.
abstract: Ubiquitin is a 76-amino acid protein involved in the targeting for destruction of proteins in the cell. The protein can readily be synthesized chemically affording an extra dimension to studies of protein stability. Ubiquitin with various modifications to the hydrophobic core has been synthesized. In particular, two core amino acids have been replaced by aminobutyric acid (Val-26) and norvaline (for Ile-30) and the product crystallized. The refined crystal structure shows an overall contraction of the molecule and the side chain of Nva-30 rotates relative to Ile-30. However, the side chain rotation is not sufficient to compensate for the effect of the loss of the methyl group and hence a small cavity is introduced into the structure, which decreases the stability of the protein. The biological behaviour of the modified protein is unaltered. The observed changes in stability are of the magnitude expected for the removal of methyl groups from the hydrophobic core of a protein. Interestingly, the effect appears to be independent of the position of the removed methyl group. The intact structure, but not its stability, is important for recognition by the biological conjugating system.
authors.affiliation: Department of Chemistry, University of Edinburgh, King's Buildings, West Mains Road, Edinburgh EH9 3JJ, Scotland, U.K.
authors.forename: S G
authors.initials: SG
authors.lastname: Love
authors.forename: T W
authors.initials: TW
authors.lastname: Muir
authors.forename: R
authors.initials: R
authors.lastname: Ramage
authors.forename: K T
authors.initials: KT
authors.lastname: Shaw
authors.forename: D
authors.initials: D
authors.lastname: Alexeev
authors.forename: L
authors.initials: L
authors.lastname: Sawyer
authors.forename: S M
authors.initials: SM
authors.lastname: Kelly
authors.forename: N C
authors.initials: NC
authors.lastname: Price
authors.forename: J E
authors.initials: JE
authors.lastname: Arnold
authors.forename: M P
authors.initials: MP
authors.lastname: Mee
authors.forename: R J
authors.initials: RJ
authors.lastname: Mayer
mesh_terms: D000613:Aminobutyrates / Q000737:chemistry; D000818:Animals; D002417:Cattle; D002942:Circular Dichroism; D018360:Crystallography, X-Ray; D006860:Hydrogen Bonding; D008958:Models, Molecular; D011487:Protein Conformation; D011489:Protein Denaturation; D014452:Ubiquitins / Q000031:analogs & derivatives / Q000138:chemical synthesis / Q000737:chemistry* / Q000302:isolation & purification; D014633:Valine / Q000031:analogs & derivatives / Q000737:chemistry
chemical_list: D000613:Aminobutyrates; D014452:Ubiquitins; C012223:alpha-aminobutyric acid; C005313:norvaline; D014633:Valine