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J. Biol. Chem., Vol. 282, Issue 6, 3713-3719, February 9, 2007

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In Vitro Polymerization of a Functional Escherichia coli Amyloid Protein^*

From the Department of Molecular, Cellular and Developmental Biology, University of Michigan, Ann Arbor, Michigan 48109

Amyloid formation is characterized by the conversion of soluble proteins into biochemically and structurally distinct fibers. Although amyloid formation is traditionally associated with diseases such as Alzheimer disease, a number of biologically functional amyloids have recently been described. Curli are amyloid fibers produced by Escherichia coli that contribute to biofilm formation and other important physiological processes. We characterized the polymerization properties of the major curli subunit protein CsgA. CsgA polymerizes into an amyloid fiber in a sigmoidal kinetic fashion with a distinct lag, growth, and stationary phase. Adding sonicated preformed CsgA fibers to the polymerization reaction can significantly shorten the duration of the lag phase. We also demonstrate that the conversion of soluble CsgA into an insoluble fiber involves the transient formation of an intermediate similar to that characterized for several disease-associated amyloids. The CsgA core amyloid domain can be divided into five repeating units that share sequence and structural hallmarks. We show that peptides representing three of these repeating units are amyloidogenic in vitro. Although the defining characteristics of CsgA polymerization appear conserved with disease-associated amyloids, these proteins evolved in diverse systems and for different purposes. Therefore, amyloidogenesis appears to be an innate protein folding pathway that can be capitalized on to fulfill normal physiological tasks.

Received for publication, September 29, 2006 , and in revised form, November 22, 2006.

^* This work was supported by National Institutes of Health Grant Award Number K22A1054967 and by the Michigan Alzheimer's Disease Research Center (MADRC) and National Institutes of Health Award P50-A608671 (to M. R. C.). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

¹ To whom correspondence should be addressed: Dept. of Molecular, Cellular and Developmental Biology, University of Michigan, 830 N. University, Ann Arbor, MI 48109. Tel.: 734-764-7592; Fax: 734-647-0884; E-mail: chapmanm{at}umich.edu.

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