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Characterization of membrane components of the flask-shaped mycoplasma Mycoplasma mobile
M Fischer1, M H Shirvan, M W Platt
1Institut für Mikrobiologie und Tierseuchen, Tierärztliche Hochschule, Hannover, FRG.
Abstract:
The cell membrane of Mycoplasma mobile was isolated by either ultrasonic or French press treatment of intact cells. The membrane fraction contained all of the cellular lipids, but only one-third of cellular proteins and had a density of 1.14 g ml-1. The soluble fraction contained the NADH dehydrogenase activity of the cells, as well as a protein with an apparent molecular mass of 55 kDa that was phosphorylated in the presence of ATP. Lipid analyses of M. mobile membranes revealed that membrane lipid could be labelled by radioactive glycerol, oleate and to a much higher extent by palmitate but not by acetic acid. The membrane lipid fraction was composed of 54% neutral and 46% polar lipid. The major constituents of the neutral lipid fraction were free fatty acid, free cholesterol and cholesterol esters (45, 25 and 20%, respectively, of total neutral lipid fraction). The free cholesterol count was 13% (w/w) of total membrane lipids with a cholesterol:phospholipid molar ratio of about 0.9. Among the polar lipids, both phospho- and glycolipids were detected. The phospholipid fraction consisted of a major de novo-synthesized phosphatidylglycerol (approximately 63% of total phospholipids), plus exogenous phosphatidylcholine and sphingomyelin incorporated in an unchanged form from the growth medium. The glycolipid fraction was dominated by a single glycolipid (approximately 90% of total glycolipids) that was preferentially labelled by palmitic acid and showed a very high saturated:unsaturated fatty acids ratio.
Insights
This study isolated Mycoplasma mobile cell membranes, revealing their lipid composition. Key findings include the high content of neutral lipids, particularly free fatty acids and cholesterol, and the presence of specific phospholipids and a unique glycolipid.
Area of Science:
- Microbiology
- Cell Biology
- Biochemistry
Background:
- Mycoplasma mobile is a unique bacterium lacking a cell wall.
- Understanding its cell membrane composition is crucial for comprehending its biological functions and interactions.
Purpose of the Study:
- To isolate and characterize the cell membrane of Mycoplasma mobile.
- To analyze the lipid and protein composition of the isolated membrane.
Main Methods:
- Cell membrane isolation using ultrasonic or French press treatment.
- Lipid analysis involving radioactive labeling (glycerol, oleate, palmitate).
- Protein analysis including molecular mass determination and phosphorylation assays.
Main Results:
- Isolated membrane contained all cellular lipids and one-third of cellular proteins.
- Neutral lipids constituted 54% of membrane lipids, dominated by free fatty acids, free cholesterol, and cholesterol esters.
- Polar lipids included phosphatidylglycerol, phosphatidylcholine, sphingomyelin, and a major glycolipid rich in saturated fatty acids.
Conclusions:
- Mycoplasma mobile cell membranes are rich in neutral lipids, including significant amounts of cholesterol.
- The membrane possesses a distinct lipid profile with a de novo synthesized phosphatidylglycerol and a unique glycolipid.
- These findings provide insights into the structural and functional properties of Mycoplasma mobile membranes.