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Originally published In Press as doi:10.1074/jbc.M006837200 on September 11, 2000

J. Biol. Chem., Vol. 275, Issue 51, 39900-39906, December 22, 2000
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Release of the Neocarzinostatin Chromophore from the Holoprotein Does Not Require Major Conformational Change of the Tertiary and Secondary Structures Induced by Trifluoroethanol*

G. Christopher, P. Sudhahar, Krishnaswamy Balamurugan, and Der-Hang ChinDagger

From the Department of Chemistry, National Changhua University of Education, Changhua 50058, Taiwan, Republic of China

Neocarzinostatin is a potent enediyne antitumor antibiotic complex in which a chromophore is noncovalently bound to a carrier protein. The protein regulates availability of the drug by proper release of the biologically active chromophore. To understand the physiological mechanism of the drug delivery system, we have examined the trifluoroethanol (TFE)-induced conformational changes of the protein with special emphasis on their relation to the release of the chromophore from holoneocarzinostatin. The effect of the alpha  helix-inducing agent, TFE, on all the beta -sheet neocarzinostatin proteins was studied by circular dichroism, fluorescence, and 1H NMR studies. By using binding of anilinonaphthalene sulfonic acid as a probe, we observed that the protein exists in a stable, partially structured intermediate state around 45-50% TFE, which is consistent with the results from tryptophan fluorescence and circular dichroism studies. The native state is stable until 20% TFE and is half-converted into the intermediate state at 30% TFE, which starts to collapse beyond 50%. High pressure liquid chromatographic analysis of the release of the chromophore caused by TFE treatment at 0 °C suggests that the release process, which occurs below 20% TFE, does not result from an observable conformational change in the protein. Kinetic measurements of the release of chromophore at 25 °C reveal that TFE does stimulate the rate of release, which increases sharply at 15% and reaches a maximum at 20% TFE, although no major secondary or tertiary structural change of the carrier protein is observed under these same conditions. Our data suggest that chromophore release results from a fluctuation of the protein structure that is stimulated by TFE. Complete release of the chromophore occurs at TFE concentrations where no overall observable unfolding of the apoprotein is seen. Thus, the results suggest that denaturation of the protein by TFE is not a necessary step for release of the tightly bound chromophore.


* This work was supported by Laboratory Grant DOH88-HR-807 from National Health Research Institutes and Individual Grant NSC 88-2113-M-018-001 from the National Science Council, The Executive Yuan, Republic of China.The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

Dagger To whom correspondence should be addressed: Dept. of Chemistry, National Changhua University of Education, Changhua 50058, Taiwan, Republic of China. Fax: 886-4-7211178 or 886-4-7211190; E-mail: chdhchin@cc.ncue.edu.tw.


Copyright © 2000 by The American Society for Biochemistry and Molecular Biology, Inc.
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