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Volume 271, Number 45, Issue of November 8, 1996 pp. 28057-28063
©1996 by The American Society for Biochemistry and Molecular Biology, Inc.

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Processing of Colicin V-1, a Secretable Marker Protein of a Bacterial ATP Binding Cassette Export System, Requires Membrane Integrity, Energy, and Cytosolic Factors

(Received for publication, June 7, 1996, and in revised form, August 7, 1996)

Xiaotian Zhong , Roberto Kolter ^§ and Phang C. Tai

From the  Department of Biology, Georgia State University, Atlanta, Georgia 30303 and ^§ Department of Microbiology and Molecular Genetics, Harvard Medical School, Boston, Massachusetts 02115

Extracellular secretion of the peptide antibiotic colicin V (ColV) in Escherichia coli is mediated by a dedicated exporter system consisting of host TolC protein and the products of two specific genes, cvaA and cvaB, the latter being a member of the ATP binding cassette (ABC) superfamily. An amino-terminal export signal of ColV is specific for the CvaA-CvaB-TolC exporter and is processed concomitant with secretion. In this study, we attempt to characterize this processing with a secretable marker protein, ColV-1, using a newly developed in vitro assay. Processing is found to be dependent on both CvaA-CvaB transporters and the TolC protein and to require membrane integrity. An additional cytoplasmic soluble factor(s) is also necessary for the processing. Although the sequence of the cleavage site suggests it could be a substrate, ColV-1 cannot be processed in vitro by the purified leader peptidase I. Moreover, ColV-1 processing is inhibited by antipain and N-ethylmaleimide. Furthermore, the processing requires energy in the form of nucleotide hydrolysis. These results indicate that the processing of ColV-1 is specific and more complex than expected, requiring the CvaA-CvaB-TolC transporter intact in the membrane, energy, and cytosolic factors for rapid cleavage.

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