title: Interaction of recombinant granulocyte colony stimulating factor with lipid membranes: enhanced stability of a water-soluble protein after membrane insertion.
abstract: The interaction of recombinant granulocyte colony stimulating factor (rhG-CSF) with lipid vesicles was studied. In the presence of dioleoylphosphatidylglycerol (DOPG) vesicles, the intrinsic fluorescence of rhG-CSF exhibits dramatic changes. In particular, tryptophan fluorescence is greatly enhanced and the emission maximum shifted to lower wavelengths. The presence of DOPG vesicles causes the protein tryptophans to become inaccessible to iodide, a water-soluble quencher of tryptophan fluorescence, yet accessible to quenching via energy transfer to pyrenyl decanoic acid, a lipid-soluble fluorescent probe. The data suggest that rhG-CSF inserts into lipid vesicles composed of DOPG. The driving force for the insertion may be a conformational change induced by the low pH at the lipid-water interface of DOPG vesicles. The DOPG-inserted form of rhG-CSF retains biological activity and shows remarkable stability, even under high-temperature conditions which lead to denaturation of rhG-CSF alone. Membrane insertion of G-CSF may be involved in the in vivo activity of this important cytokine.
authors.affiliation: Department of Pharmaceutics and Drug Delivery, Amgen, Inc., Amgen Center, Thousand Oaks, California 91320.
authors.forename: D
authors.initials: D
authors.lastname: Collins
authors.forename: Y
authors.initials: Y
authors.lastname: Cha
mesh_terms: D003652:Decanoic Acids / Q000378:metabolism; D004355:Drug Stability; D004735:Energy Transfer; D005453:Fluorescence; D005456:Fluorescent Dyes; D016179:Granulocyte Colony-Stimulating Factor / Q000378:metabolism*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008081:Liposomes / Q000378:metabolism*; D010715:Phosphatidylglycerols / Q000378:metabolism*; D011487:Protein Conformation; D011489:Protein Denaturation; D011994:Recombinant Proteins / Q000494:pharmacology; D012995:Solubility; D013050:Spectrometry, Fluorescence; D014364:Tryptophan / Q000378:metabolism; D014443:Tyrosine / Q000378:metabolism; D014867:Water
chemical_list: D003652:Decanoic Acids; D005456:Fluorescent Dyes; D008081:Liposomes; D010715:Phosphatidylglycerols; D011994:Recombinant Proteins; D014867:Water; D016179:Granulocyte Colony-Stimulating Factor; D014443:Tyrosine; C021247:pyrenedecanoic acid; C051388:1,2-dioleoyl-sn-glycero-3-phosphoglycerol; D014364:Tryptophan