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J. Biol. Chem., Vol. 283, Issue 39, 26748-26758, September 26, 2008

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β-Barrel Proteins That Reside in the Escherichia coli Outer Membrane in Vivo Demonstrate Varied Folding Behavior in Vitro^*

From the T. C. Jenkins Department of Biophysics, Johns Hopkins University, Baltimore, Maryland 21218

Little is known about the dynamic process of membrane protein folding, and few models exist to explore it. In this study we doubled the number of Escherichia coli outer membrane proteins (OMPs) for which folding into lipid bilayers has been systematically investigated. We cloned, expressed, and folded nine OMPs: outer membrane protein X (OmpX), OmpW, OmpA, the crcA gene product (PagP), OmpT, outer membrane phospholipase A (OmpLa), the fadl gene product (FadL), the yaet gene product (Omp85), and OmpF. These proteins fold into the same bilayer in vivo and share a transmembrane β-barrel motif but vary in sequence and barrel size. We quantified the ability of these OMPs to fold into a matrix of bilayer environments. Several trends emerged from these experiments: higher pH values, thinner bilayers, and increased bilayer curvature promote folding of all OMPs. Increasing the incubation temperature promoted folding of several OMPs but inhibited folding of others. We discovered that OMPs do not have the same ability to fold into any single bilayer environment. This suggests that although environmental factors influence folding, OMPs also have intrinsic qualities that profoundly modulate their folding. To rationalize the differences in folding efficiency, we performed kinetic and thermal denaturation experiments, the results of which demonstrated that OMPs employ different strategies to achieve the observed folding efficiency.

Received for publication, April 9, 2008 , and in revised form, July 18, 2008.

^* This work was supported by Grant MCB0423807 from the National Science Foundation. 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 supplemental Fig. S1 and table S1.

¹ To whom correspondence should be addressed: 3400 N. Charles St., Baltimore, MD 21218. Tel.: 410-516-7256; Fax: 410-516-5451; E-mail: karen.fleming{at}jhu.edu.

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