Open AccessStructural and Functional Analyses of the Major Outer Membrane Protein ofChlamydia trachomatis
Author(s) -
Guoqiang Sun,
Sukumar Pal,
Annahita Sarcon,
Soyoun Kim,
Etsuko Sugawara,
Hiroshi Nikaido,
Melanie J. Cocco,
Ellena M. Peterson,
Luis M. de la Maza
Publication year - 2007
Publication title -
journal of bacteriology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.652
H-Index - 246
eISSN - 1067-8832
pISSN - 0021-9193
DOI - 10.1128/jb.00552-07
Subject(s) - porin , trimer , bacterial outer membrane , circular dichroism , biology , gel electrophoresis , sodium dodecyl sulfate , protein quaternary structure , chlamydia trachomatis , membrane protein , polyacrylamide gel electrophoresis , biochemistry , size exclusion chromatography , protein structure , biophysics , membrane , dimer , chemistry , escherichia coli , enzyme , organic chemistry , protein subunit , immunology , gene
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 fromChlamydia 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 β-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 ofC. trachomatis is a trimer with predominantly a β-sheet structure and porin function.