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  • Title: Conformational changes during apoplastocyanin folding observed by photocleavable modification and transient grating.
    Author: Hirota S, Fujimoto Y, Choi J, Baden N, Katagiri N, Akiyama M, Hulsker R, Ubbink M, Okajima T, Takabe T, Funasaki N, Watanabe Y, Terazima M.
    Journal: J Am Chem Soc; 2006 Jun 14; 128(23):7551-8. PubMed ID: 16756310.
    Abstract:
    A new method to investigate the initial protein folding dynamics is developed based on a pulsed laser light triggering method and a unique transient grating method. The side chain of the cysteine residue of apoplastocyanin (apoPC) was site-specifically modified with a 4,5-dimethoxy-2-nitrobenzyl derivative, where the CD and 2D NMR spectra showed that the modified apoPC was unfolded. The substituent was cleaved with a rate of about 400 ns by photoirradiation, which was monitored by the disappearance of the absorption band at 355 nm and the increase in the transient grating signal. After a sufficient time from the photocleavage reaction, the CD and NMR spectra showed that the native beta-sheet structure was recovered. Protein folding dynamics was monitored in the time domain with the transient grating method from a viewpoint of the molecular volume change and the diffusion coefficient, both of which reflect the global structural change, including the protein-water interaction. The observed volume decrease of apoPC with a time scale of 270 micros is ascribed to the initial hydrophobic collapse. The increase in the diffusion coefficient (23 ms) is considered to indicate a change from an intermolecular to an intramolecular hydrogen bonding network. The initial folding process of apoPC is discussed based on these observations.
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