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Journal of Bacteriology, September 2007, p. 6222-6235, Vol. 189, No. 17
0021-9193/07/$08.00+0     doi:10.1128/JB.00552-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Structural and Functional Analyses of the Major Outer Membrane Protein of Chlamydia trachomatis{triangledown}

Guifeng Sun,1 Sukumar Pal,1 Annahita K. Sarcon,1 Soyoun Kim,1 Etsuko Sugawara,2 Hiroshi Nikaido,2 Melanie J. Cocco,3 Ellena M. Peterson,1 and Luis M. de la Maza1*

Department of Pathology and Laboratory Medicine, Medical Sciences, Room D440, University of California, Irvine, Irvine, California 92697-4800,1 Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, California 94720-3202,2 Department of Molecular Biology and Biochemistry, 1218 Natural Sciences 1, University of California, Irvine, Irvine, California 92697-39003

Received 11 April 2007/ Accepted 20 June 2007

Chlamydia trachomatis is a major pathogen throughout the world, and preventive measures have focused on the production of a vaccine using the major outer membrane protein (MOMP). Here, in elementary bodies and in preparations of the outer membrane, we identified native trimers of the MOMP. The trimers were stable under reducing conditions, although disulfide bonds appear to be present between the monomers of a trimer and between trimers. Cross-linking of the outer membrane complex demonstrated that the MOMP is most likely not in a close spatial relationship with the 60- and 12-kDa cysteine-rich proteins. Extraction of the MOMP from Chlamydia isolates under nondenaturing conditions yielded the trimeric conformation of this protein as shown by cross-linking and analysis by sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis with different concentrations of acrylamide. Using circular dichroism spectroscopy, we determined that the trimers were formed mainly of ß-pleated sheet structures in detergent micelles. Using a liposomal swelling assay, the MOMP was found to have porin activity, and the size of the pore was estimated to be approximately 2 nm in diameter. The trimers were found to be stable in SDS at temperatures ranging from 4 to 37°C and over a pH range of 5.0 to 8.0. In addition, the trimers of MOMP were found to be resistant to digestion with trypsin. In conclusion, these results show that the native conformation of the MOMP of C. trachomatis is a trimer with predominantly a ß-sheet structure and porin function.

* Corresponding author. Mailing address: Department of Pathology and Laboratory Medicine, Medical Sciences, Room D440, University of California, Irvine, Irvine, CA 92697-4800. Phone: (949) 824-7450. Fax: (949) 824-2160. E-mail: lmdelama{at}uci.edu

{triangledown} Published ahead of print on 29 June 2007.

Journal of Bacteriology, September 2007, p. 6222-6235, Vol. 189, No. 17
0021-9193/07/$08.00+0     doi:10.1128/JB.00552-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.



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