Detection and characterization of an ovine placental lactogen stable intermediate in the urea-induced unfolding process.
The urea-induced equilibrium unfolding of ovine placental lactogen, purified from ovine placenta, was followed by size-exclusion chromatography, far-UV CD, and intrinsic tryptophan fluorescence. The data obtained by each of these methods showed a poor fit to a two-state model involving only a native and an unfolded form. A satisfactory fit required, instead, a model that involved a stable, partially folded form in addition to the native and unfolded ones. The results obtained from the best-fitting theoretical curves for the three-state model indicated that this intermediate state, which is the predominant species in solution at 3.6 M of urea activity, is compact, largely alpha-helical, and changes considerably the native-like tertiary packing around its tryptophan residues. These findings suggest that this stable intermediate exhibits properties similar to those that characterize the molten globule state.
Cymes
G D
GD
Insituto de Química y Fisicoquímica Biológicas, Facultad de Farmacia y Bioquímica, UBA, Buenos Aires, Argentina. gdcymes@criba.edu.ar
Grosman
C
C
Delfino
J M
JM
Wolfenstein-Todel
C
C
D000818:Animals; D002850:Chromatography, Gel; D002942:Circular Dichroism; D005260:Female; D010928:Placental Lactogen / Q000737:chemistry* / Q000187:drug effects; D011487:Protein Conformation; D011489:Protein Denaturation / Q000187:drug effects; D017510:Protein Folding; D012756:Sheep; D013050:Spectrometry, Fluorescence; D014508:Urea / Q000494:pharmacology*
D014508:Urea; D010928:Placental Lactogen