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Updated: Feb 6, 2026
From Constructs to Crystals – Towards Structure Determination of β-barrel Outer Membrane Proteins
Published on: July 4, 2016
Spectroscopic analysis of chlamydial major outer membrane protein in support of structure elucidation
Robert W Hepler1, Debbie D Nahas1, Bob Lucas1
1Infectious Diseases and Vaccines Discovery, MRL, Merck & Co., Inc., Kenilworth, New Jersey.
Abstract:
Chlamydial major outer membrane protein (MOMP) is the major protein constituent of the bacterial pathogen Chlamydia trachomatis. Chlamydia trachomatis Serovars D-K are the leading cause of genital tract infections which can lead to infertility or ectopic pregnancies. A vaccine against Chlamydia is highly desirable but currently not available. MOMP accounts for ~ 60% of the chlamydial protein mass and is considered to be one of the lead vaccine candidates against C. trachomatis. We report on the spectroscopic analysis of C. trachomatis native MOMP Serovars D, E, F, and J as well as C. muridarum MOMP by size exclusion chromatography multi angle light scattering (SEC MALS), circular dichroism (CD) and attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR). MOMP was purified from the native bacterium grown in either adherent HeLa cells or in different suspension cell lines. Our results confirm that MOMP forms homo-trimers in detergent micelles. The secondary structure composition of C. trachomatis MOMP was conserved across serovars, but different from composition of C. muridarum MOMP with a 13% (CD) to 18% (ATR-FTIR) reduction in β-sheet conformation for C. trachomatis MOMP. When Serovar E MOMP was isolated from suspension cell lines the α-helix content increased by 7% (CD) to 13% (ATIR-FTIR). Maintenance of a native-like tertiary and quaternary structure in subunit vaccines is important for the generation of protective antibodies. This biophysical characterization of MOMP presented here serves, in the absence of functional assays, as a method for monitoring the structural integrity of MOMP.
Insights
Chlamydia trachomatis major outer membrane protein (MOMP) forms trimers and its structure is conserved across serovars. This biophysical analysis of MOMP provides a method to monitor vaccine candidate structural integrity.
Area of Science:
- Microbiology
- Structural Biology
- Vaccine Development
Background:
- Chlamydia trachomatis causes genital infections, potentially leading to infertility.
- A Chlamydia vaccine is needed, with major outer membrane protein (MOMP) as a key candidate.
- Understanding MOMP structure is crucial for effective vaccine design.
Purpose of the Study:
- To spectroscopically analyze native Chlamydia trachomatis and Chlamydia muridarum MOMP.
- To confirm MOMP's quaternary structure and assess secondary structure composition.
- To establish a method for monitoring MOMP structural integrity for vaccine development.
Main Methods:
- Purification of native MOMP from bacteria grown in cell lines.
- Size exclusion chromatography multi-angle light scattering (SEC-MALS) for structural analysis.
- Circular dichroism (CD) and attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) for secondary structure determination.
Main Results:
- MOMP forms stable homo-trimers in detergent micelles.
- Chlamydia trachomatis MOMP showed conserved secondary structure across serovars D, E, F, and J.
- Chlamydia trachomatis MOMP had a reduced beta-sheet content compared to Chlamydia muridarum MOMP.
- Isolation from suspension cells altered Serovar E MOMP's alpha-helix content.
Conclusions:
- Native MOMP exists as a trimer, a critical feature for vaccine potential.
- Biophysical characterization confirms conserved structure in C. trachomatis MOMP, but differences exist with C. muridarum MOMP.
- This spectroscopic analysis method is vital for ensuring the structural integrity of MOMP-based vaccines.
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