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A Chlamydia pneumoniae adhesin induces phosphatidylserine exposure on host cells
Jan N Galle1, Tim Fechtner1, Thorsten Eierhoff2,3,4,5
1Lehrstuhl für Funktionelle Genomforschung der Mikroorganismen, Heinrich-Heine-University Düsseldorf, Universitätsstraße 1, 40225, Düsseldorf, Germany.
Abstract:
In mammalian cells, the internal and external leaflets of the plasma membrane (PM) possess different phospholipids. Phosphatidylserine (PS) is normally confined to the inner (cytoplasmic) membrane leaflet. Here we report that the adhesin CPn0473 of the human pathogenic bacterium Chlamydia pneumoniae (Cpn) binds to the PM of human cells and induces PS externalization but unexpectedly not apoptosis. PS externalization is increased in human cells exposed to infectious Cpn cells expressing increased CPn0473 and reduced in exposure to Cpn expressing decreased CPn0473. CPn0473 binds specifically to synthetic membranes carrying PS and stimulates pore formation. Asymmetric giant unilamellar vesicles (GUVs) in which PS is restricted to the inner leaflet reveal that CPn0473 induces PS externalization in the absence of other proteins. Thus our identification of CPn0473 as a bacterial PS translocator capable of specific and apoptosis-independent PS externalization during infection extends the spectrum of mechanisms intracellular pathogens use to enter host cells.
Insights
The adhesin CPn0473 from Chlamydia pneumoniae induces externalization of phosphatidylserine (PS) in human cells without causing apoptosis. This bacterial protein acts as a PS translocator, facilitating host cell entry.
Area of Science:
- Cell Biology
- Microbiology
- Biochemistry
Background:
- Mammalian plasma membranes exhibit asymmetric phospholipid distribution.
- Phosphatidylserine (PS) is typically localized to the inner leaflet of the plasma membrane.
- Apoptosis involves the externalization of PS.
Purpose of the Study:
- To investigate the role of Chlamydia pneumoniae adhesin CPn0473 in phosphatidylserine (PS) externalization.
- To determine if CPn0473-induced PS externalization is linked to apoptosis.
- To elucidate the mechanism by which CPn0473 affects membrane phospholipids.
Main Methods:
- Utilized human cells and synthetic membranes to study CPn0473 interactions.
- Assessed PS externalization using flow cytometry and microscopy.
- Employed asymmetric giant unilamellar vesicles (GUVs) to model membrane asymmetry.
- Quantified PS externalization in response to varying levels of CPn0473 expression.
Main Results:
- CPn0473 binding to human cells induced significant PS externalization.
- PS externalization occurred independently of apoptosis.
- CPn0473 specifically bound to PS-containing membranes and induced pore formation.
- Increased CPn0473 expression correlated with higher PS externalization.
Conclusions:
- CPn0473 functions as a bacterial phosphatidylserine (PS) translocator.
- This mechanism allows for apoptosis-independent PS externalization during Chlamydia pneumoniae infection.
- CPn0473 contributes to novel host cell entry mechanisms employed by intracellular pathogens.
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