title: Role of disulfide bridges in determining the biological activity of interleukin 3.
abstract: Total chemical synthesis of analog proteins was used to examine the requirement for specific disulfide bridges for the biological activity of interleukin 3 (IL-3), a growth factor that stimulates multiple lineages of hemopoietic cells. Four structural analogs of the mature, 140 amino acid murine IL-3 molecule were synthesized in which specific cysteine residues were replaced by alanines. In a quantitative IL-3 assay, based on [3H]thymidine incorporation into factor-dependent cells, the IL-3 analog with alanines substituted for all four cysteines--i.e., [Ala17,79,80,140]IL-3--had 1/500th as much activity as the molecule synthesized according to the native sequence. The two analogs [Cys17,79,Ala80,140]IL-3 and [Cys17,140,Ala79,80]IL-3 had similarly low activity, whereas the [Cys17,80,Ala79,140]IL-3 analog had 2000-fold higher activity than these three analogs, and 3-fold higher than the molecule with the native sequence. This shows that in IL-3 a single disulfide bridge, between cysteines 17 and 80, is required for biological activity that approximates physiological levels. This disulfide probably stabilizes the tertiary structure of the protein to give a conformation that is optimal for function.
authors.affiliation: Division of Biology, California Institute of Technology, Pasadena 91125.
authors.forename: I
authors.initials: I
authors.lastname: Clark-Lewis
authors.forename: L E
authors.initials: LE
authors.lastname: Hood
authors.forename: S B
authors.initials: SB
authors.lastname: Kent
mesh_terms: D000409:Alanine; D000595:Amino Acid Sequence; D002851:Chromatography, High Pressure Liquid; D003545:Cysteine; D004247:DNA / Q000032:analysis; D004220:Disulfides / Q000032:analysis*; D006801:Humans; D007377:Interleukin-3 / Q000032:analysis / Q000502:physiology*; D008969:Molecular Sequence Data; D010449:Peptide Mapping; D013329:Structure-Activity Relationship
chemical_list: D004220:Disulfides; D007377:Interleukin-3; D004247:DNA; D003545:Cysteine; D000409:Alanine