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The major outer membrane protein of Chlamydia psittaci functions as a porin-like ion channel
S Wyllie1, R H Ashley, D Longbottom
1Moredun Research Institute, International Research Centre, Pentland Science Park, Penicuik, Midlothian EH26 0PZ, United Kingdom.
Abstract:
The major outer membrane protein (MOMP) of Chlamydia species shares several biochemical properties with classical porin proteins. Secondary structure analysis by circular dichroism now reveals that MOMP purified from Chlamydia psittaci has a predominantly beta-sheet content (62%), which is also typical of bacterial porins. Can MOMP form functional ion channels? To directly test the "porin channel" hypothesis at the molecular level, the MOMP was reconstituted into planar lipid bilayers, where it gave rise to multibarreled channels, probably trimers, which were modified by an anti-MOMP monoclonal antibody. These observations are consistent with the well-characterized homo-oligomeric nature of MOMP previously revealed by biochemical analysis and with the triple-barreled behavior of other porins. MOMP channels were weakly anion selective (PCl/PK approximately 2) and permeable to ATP. They may therefore be a route by which Chlamydia can take advantage of host nucleoside triphosphates and explain why some anti-MOMP antibodies neutralize infection. These findings have broad implications on the search for an effective chlamydial vaccine to control the significant human and animal diseases caused by these organisms.
Insights
The major outer membrane protein (MOMP) of Chlamydia forms functional, multi-barreled ion channels, similar to bacterial porins. These channels allow ATP passage, potentially explaining Chlamydia
Area of Science:
- Microbiology
- Structural Biology
- Biophysics
Background:
- The major outer membrane protein (MOMP) of Chlamydia species exhibits biochemical similarities to bacterial porins.
- Understanding MOMP's structure and function is crucial for developing chlamydial vaccines.
Purpose of the Study:
- To investigate whether MOMP can form functional ion channels.
- To elucidate the channel properties of MOMP at a molecular level.
Main Methods:
- Secondary structure analysis using circular dichroism.
- Reconstitution of purified MOMP into planar lipid bilayers.
- Electrophysiological measurements of reconstituted channels.
Main Results:
- Circular dichroism revealed MOMP has a predominantly beta-sheet structure (62%), characteristic of porins.
- Reconstituted MOMP formed multi-barreled ion channels, likely trimers, in lipid bilayers.
- These MOMP channels were weakly anion selective and permeable to ATP.
Conclusions:
- MOMP functions as a porin-like channel, facilitating nutrient uptake (e.g., ATP) from the host.
- The channel activity and trimeric structure of MOMP provide insights into Chlamydia pathogenesis.
- These findings have significant implications for designing effective chlamydial vaccines.