title: Unfolding intermediate of a multidomain protein, calmodulin, in urea as revealed by small-angle X-ray scattering.
abstract: The denaturation of calmodulin (CaM) induced by urea has been studied by small-angle X-ray scattering, which is a direct way to evaluate the shape changes in a protein molecule. In the absence of Ca(2+), the radii of gyration (R(g)) of CaM are 20.8+/-0.3 A in the native state and about 34+/-1.0 A in the unfolded state. The transition curve derived from Kratky plots indicates a bimodal transition via a stable unfolding intermediate around 2.5 M urea. In the presence of Ca(2+) and in the presence of both Ca(2+) and a target peptide, the R(g) values are 21.5+/-0.3 and 18.1+/-0.3 A in the native state and 26.7+/-0.4 and 24.9+/-0.4 A at 9 M urea, respectively. The results indicate that a stable unfolding intermediate still persists in 9 M urea. The present results suggest that the shape of unfolding intermediates is an asymmetric dumbbell-like structure, one in the folded and one in the unfolded state.
authors.affiliation: Graduate School of Science and Engineering, Yamagata University, 4-3-16 Jo-nan, 992-8510 Yonezawa, Japan.
authors.forename: Tsuyoshi
authors.initials: T
authors.lastname: Yokouchi
authors.forename: Yoshinobu
authors.initials: Y
authors.lastname: Izumi
authors.forename: Tomohiro
authors.initials: T
authors.lastname: Matsufuji
authors.forename: Yuji
authors.initials: Y
authors.lastname: Jinbo
authors.forename: Hidenori
authors.initials: H
authors.lastname: Yoshino
mesh_terms: D002147:Calmodulin / Q000737:chemistry* / Q000187:drug effects; D011489:Protein Denaturation; D017510:Protein Folding; D017434:Protein Structure, Tertiary; D014508:Urea / Q000494:pharmacology*; D014961:X-Ray Diffraction
chemical_list: D002147:Calmodulin; D014508:Urea