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J Biol Chem, Vol. 275, Issue 18, 13171-13174, May 5, 2000

ACCELERATED PUBLICATION
Atomic Force Microscopy Reveals Two Conformations of the 20 S Proteasome from Fission Yeast^*

Pawel A. Osmulski and Maria Gaczynska

From the University of Texas Health Science Center at San Antonio, Institute of Biotechnology, San Antonio, Texas 78245

The proteasome is a major cytosolic proteolytic complex, indispensable in eukaryotic cells. The barrel-shaped core of this enzyme, the 20 S proteasome, is built from 28 subunits forming four stacked rings. The two inner -rings harbor active centers, whereas the two outer -rings play a structural role. Crystal structure of the yeast 20 S particle showed that the entrance to the central channel was sealed. Because of this result, the path of substrates into the catalytic chamber has remained enigmatic. We have used tapping mode atomic force microscopy (AFM) in liquid to address the dynamic aspects of the 20 S proteasomes from fission yeast. We present here evidence that, when observed with AFM, the proteasome particles in top view position have either open or closed entrance to the central channel. The preferred conformation depends on the ligands present. Apparently, the addition of a substrate to the uninhibited proteasome shifts the equilibrium toward the open conformation. These results shed new light on the possible path of the substrate into the proteolytic chamber.

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^* 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.

To whom correspondence should be addressed: University of Texas Health Science Center at San Antonio, Institute of Biotechnology, 15355 Lambda Dr., San Antonio, TX 78245. Tel.: 210-567-7262; Fax: 210-567-7247; E-mail: gaczynska@uthscsa.edu.

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

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