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J. Biol. Chem., Vol. 281, Issue 31, 21720-21727, August 4, 2006
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From the Public Health Research Institute, Newark, New Jersey 07103
In competent Bacillus subtilis, the ComG proteins are required to allow exogenous DNA to access to membrane-bound receptor ComEA during transformation. Here we describe a multimeric complex containing the pilin-like protein ComGC. Due to similarities to the type 4 pilus and the type 2 secretion system pseudopilus, we have tentatively named it the "competence pseudopilus." The ComGC multimer is released from cells upon digestion of the cell wall with lysozyme and has a heterogeneous size, estimated to range between 40 and 100 monomers, covalently linked by disulfide bonds. We determined that the prepilin peptidase ComC, the thiol-disulfide oxidoreductase pair BdbDC, and all seven ComG proteins are necessary to form the pseudopilus. Furthermore, these proteins are also sufficient to form a functional complex, i.e. able to facilitate binding of exogenous DNA to ComEA. The initial steps of pseudopilus biogenesis include the processing of ComGC in the cytoplasmic membrane and consist of two independent events, proteolytic cleavage by ComC and formation of an intramolecular disulfide bond by BdbDC. The other ComG proteins are required to assemble the mature ComGC monomers in the membrane into a multimeric complex proposed to span the cell envelope. We discuss the possible role of the competence pseudopilus in DNA binding and uptake during transformation.
Received for publication, April 28, 2006 , and in revised form, June 1, 2006.
* This work was supported by National Institutes of Health Grant GM43756. 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.
The on-line version of this article (available at http://www.jbc.org) contains additional text and references.
1 Present address: Dipartimento di Biologia, Università degli Studi di Padova, Padova 35131, Italy.
2 To whom correspondence should be addressed: Public Health Research Institute, 225 Warren St., Newark, NJ 071103. Tel.: 973-854-3400; Fax: 973-854-3401; E-mail: dubnau{at}phri.org.
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