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J. Biol. Chem., Vol. 279, Issue 30, 31495-31504, July 23, 2004

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Hydrophobic Residues of the Autotransporter EspP Linker Domain Are Important for Outer Membrane Translocation of Its Passenger^*

Jorge J. Velarde and James P. Nataro¶||**

From the Center for Vaccine Development, Departments of Biochemistry, ^¶Pediatrics, ^||Medicine, and ^**Microbiology & Immunology, University of Maryland School of Medicine, Baltimore, Maryland 21201

The autotransporter family of proteins is an important class of Gram-negative secreted virulence factors. Their secretion mechanism comprises entry to the periplasm via the Sec apparatus, followed by formation of an outer membrane barrel, which allows the N-terminal passenger domain to pass to the extracellular space. Several groups have identified a region immediately upstream of the domain that is important for outer membrane translocation, the so-called linker region. Here we characterize this region in EspP, a prototype of the serine protease autotransporters of enterobacteriaceae. We hypothesized that the folding of this region would be important in the outer membrane translocation process. We tested this hypothesis using a mutagenesis approach in conjunction with a series of nested deletions and found that in the absence of a complete passenger, mutations to the C-terminal helix, but not the upstream linker, significantly decrease secretion efficiency. However, in the presence of the passenger mutations to the amino-terminal region of the linker decrease secretion efficiency. Moreover, amino acids of hydrophobic character play a crucial role in linker function, suggesting the existence of a hydrophobic core or hydrophobic interaction necessary for outer membrane translocation of autotransporter proteins.

Received for publication, April 21, 2004 , and in revised form, May 17, 2004.

^* This work was supported by United States Public Health Service Grant AI-43615. 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.

Supported initially by NIGMS, National Institutes of Health (NIH), Initiative for Minority Students Development Grant R25-GM55036 and subsequently by NIH Minority Predoctoral Fellowship Program Award F31-AI50249.

To whom correspondence should be addressed: Center for Vaccine Development, University of Maryland, Baltimore, 685 W. Baltimore St., HSF 441, Baltimore, MD 21201. E-mail: jnataro{at}medicine.umaryland.edu.

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