Journal
JOURNAL OF MOLECULAR BIOLOGY
Volume 357, Issue 3, Pages 997-1008Publisher
ACADEMIC PRESS LTD- ELSEVIER SCIENCE LTD
DOI: 10.1016/j.jmb.2005.12.089
Keywords
protein folding; heme oxygenase; scaling relationship; coil-globule transition; small-angle X-ray scattering
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Polypeptide collapse is generally observed as the initial folding dynamics of proteins with more than 100 residues, and is suggested to be caused by the coil-globule transition explained by Flory's theory of polymers. To support the suggestion by establishing a scaling behavior between radius of gyration (R-g) and chain length for the initial folding intermediates, the folding dynamics of heme oxygenase (HO) was characterized by time-resolved, small-angle X-ray scattering. HO is a highly helical protein without disulfide bridges, and is the largest protein (263 residues) characterized by the method. The folding process of HO was found to contain a transient oligomerization; however, the conformation within 10 ms was demonstrated to be monomeric and to possess R-g of 26.1(+/- 1.1) angstrom. Together with the corresponding data for proteins with different chain lengths, the seven R-g values demonstrated the scaling relationship to chain length with a scaling exponent of 0.35 +/- 0.11, which is close to the theoretical value of 1/3 predicted for globules in solutions where monomer-monomer interactions are favored over monomer-solvent interactions (poor solvent). The finding indicated that the initial folding dynamics of proteins bears the signature of the coil-globule transition, and offers a clue to explain the folding mechanisms of proteins with different chain lengths. (c) 2006 Elsevier Ltd. All rights reserved.
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