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The cell membrane of Mycoplasma penetrans: lipid composition and phospholipase A1 activity
1Department of Membrane and Ultrastructure Research, Hebrew University-Hadassah Medical School, Jerusalem, Israel.
Abstract:
Analysis of Mycoplasma penetrans membrane lipids revealed that, in addition to large amounts of unesterified cholesterol, M. penetrans incorporated exogenous phospholipids, preferentially sphingomyelin, from the growth medium. The major phospholipids synthesized de novo by M. penetrans were phosphatidylglycerol (PG) and diphosphatidylglycerol (DPG). In vivo labeling of PG and DPG by growing the cells with radioactive palmitate or oleate, followed by snake venom phospholipase A2 treatment, enabled us to assess the positional distribution of fatty acids in these lipids. Saturated fatty acids were found preferentially in position 2 of the glycerol backbone, and not in position 1 as found elsewhere in nature, while unsaturated fatty acids prefer position 1. M. penetrans membranes contain phospholipase activity of the A1 type, removing a fatty acid from the sn-1 ester bond of phospholipids. The activity was neither stimulated by Ca2+ nor inhibited by EGTA and had a broad pH spectrum. The substrate specificity of the enzyme was investigated with various natural lipids and with a fluorescent analog of the phosphatidylcholine. The enzyme was equally active toward phosphatidylcholine and phosphatidylglycerol, but did not hydrolyze diphosphatidylglycerol. The enzyme did not act on triacylglycerol, diacylglycerol or cholesteryl ester, but low activity was detected toward monoacylglycerol. The enzyme was heat-sensitive and detergent-sensitive, and was almost completely inhibited by p-bromophenacylbromide (50 microM), but was not affected by SH reagents. This study is the first one reporting phospholipase A1 activity in Mollicutes. A possible role of this enzyme in forming lipid mediators upon the interaction of M. penetrans cells with eukaryotic cells is suggested.
Insights
Mycoplasma penetrans incorporates external phospholipids and synthesizes its own, with unique fatty acid placement. A novel phospholipase A1 activity was identified, potentially involved in host cell interactions.
Area of Science:
- Microbiology
- Lipid Biochemistry
- Molecular Biology
Background:
- Mycoplasma penetrans, a unique bacterium, has distinct membrane lipid compositions.
- Understanding lipid metabolism is crucial for Mycoplasma biology and host interactions.
Purpose of the Study:
- To analyze the lipid composition and de novo synthesis of Mycoplasma penetrans.
- To characterize the novel phospholipase A1 activity in M. penetrans.
Main Methods:
- Analysis of M. penetrans membrane lipids and exogenous phospholipid incorporation.
- In vivo labeling with radioactive fatty acids followed by phospholipase A2 treatment.
- Enzyme assays to determine substrate specificity and inhibition of phospholipase A1.
Main Results:
- M. penetrans incorporates exogenous sphingomyelin and synthesizes phosphatidylglycerol (PG) and diphosphatidylglycerol (DPG).
- Fatty acids exhibit unusual positional distribution in PG and DPG: saturated at position 2, unsaturated at position 1.
- A novel, Ca2+-independent phospholipase A1 activity was identified, specific for phosphatidylcholine and phosphatidylglycerol.
Conclusions:
- Mycoplasma penetrans possesses unique lipid metabolism pathways with unusual fatty acid distribution.
- The discovery of phospholipase A1 activity in Mollicutes offers new insights into M. penetrans biology.
- This enzyme may play a role in lipid mediator formation during host-pathogen interactions.