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Journal of Bacteriology, April 2001, p. 2399-2404, Vol. 183, No. 8
0021-9193/01/$04.00+0   DOI: 10.1128/JB.183.8.2399-2404.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.

Molecular Sieve Mechanism of Selective Release of Cytoplasmic Proteins by Osmotically Shocked Escherichia coli

Nora Vázquez-Laslop, Hyunwoo Lee, Rong Hu, and Alex A. Neyfakh*

Center for Pharmaceutical Biotechnology, University of Illinois, Chicago, Illinois 60607

Received 8 November 2000/Accepted 18 January 2001

Escherichia coli cells, the outer membrane of which is permeabilized with EDTA, release a specific subset of cytoplasmic proteins upon a sudden drop in osmolarity in the surrounding medium. This subset includes EF-Tu, thioredoxin, and DnaK among other proteins, and comprises ~10% of the total bacterial protein content. As we demonstrate here, the same proteins are released from electroporated E. coli cells pretreated with EDTA. Although known for several decades, the phenomenon of selective release of proteins has received no satisfactory explanation. Here we show that the subset of released proteins is almost identical to the subset of proteins that are able to pass through a 100-kDa-cutoff cellulose membrane upon molecular filtration of an E. coli homogenate. This finding indicates that in osmotically shocked or electroporated bacteria, proteins are strained through a molecular sieve formed by the transiently damaged bacterial envelope. As a result, proteins of small native sizes are selectively released, whereas large proteins and large protein complexes are retained by bacterial cells.

* Corresponding author. Mailing address: Center for Pharmaceutical Biotechnology (M/C 870), University of Illinois, 900 S. Ashland Ave., Chicago, IL 60607. Phone: (312) 996-7231. Fax: (312) 413-9303. E-mail: neyfakh{at}uic.edu.

Journal of Bacteriology, April 2001, p. 2399-2404, Vol. 183, No. 8
0021-9193/01/$04.00+0   DOI: 10.1128/JB.183.8.2399-2404.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.


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