Mycoplasma Cell Membranes

The mycoplasmas, a trivial name used to denote organisms included in the class Mollicutes, are a group of prokaryotic organisms comprising more than 120 species distinguished from ordinary bacteria by their small size and the total lack of cell walls. The absence of a cell wall in mycoplasmas is a characteristic of outstanding importance to which the mycoplasmas owe many of their pecu liarities, for example, their morphological instability, osmotic sensitivity, unique ion pumping systems, resistance to antibiotics that interfere with cell wall bio synthesis, and susceptibility to lysis by detergents and alcohols. The fact that the mycoplasma cells contain only one membrane type, the plasma membrane, constitutes one of their most useful properties for membrane studies; once the membrane is isolated, it is uncontaminated with other mem brane types. Another advantage in using mycoplasmas as models for membrane studies stems from the fact that their membrane lipid composition can be altered in a controlled manner. This characteristic results from the partial or total inabili ty of the mycoplasmas to synthesize long-chain fatty acids and cholesterol, making mycoplasmas dependent on the supply of fatty acids from the growth medium. The ability to introduce controlled alterations in the fatty acid composi tion and cholesterol content of mycoplasma membranes has been utilized in studying the molecular organization and physical properties of biological mem branes.

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The present volume is the first attempt to bring together, in a comprehensive and comparative manner, the vast knowledge accumulated on the mycoplasma cell membranes. The state-of-the-art coverage includes physical studies of lipid organization and dynamics in mycoplasma membranes, the role of cholesterol in mycoplasma membranes, spiralins, and eight other subjects.

Inhalt
1 Mycoplasma Membranes as Models in Membrane Research.- 1. An Introduction to Mollicutes.- 2. Characterization of Mycoplasma Membranes.- 3. Elucidating Membrane Organization.- 4. Role of Membrane Components in Pathogenicity.- 5. Future Prospects.- 6. References.- 2 Mycoplasma Membrane Lipids: Chemical Composition and Transbilayer Distribution.- 1. Introduction.- 2. Lipid Composition of Mycoplasmas.- 3. Transbilayer Distribution of Lipids in A. laidlawii Membranes.- 4. Transbilayer Distribution of Sterols in Membranes of Mycoplasma Species.- 5. References.- 3 Physical Studies of Lipid Organization and Dynamics in Mycoplasma Membranes.- 1. Introduction.- 2. Physical Studies of Lipid Orientation and Dynamics.- 3. Summary and Conclusions.- 4. References.- 4 Regulation and Physicochemical Properties of the Polar Lipids in Acholeplasma laidlawii.- 1. General Features of A. laidlawii and Its Membrane.- 2. Basic Properties of the A. laidlawii Membrane.- 3. Biochemical Pathways and Chemical Structure of the Polar Lipids.- 4. Phase Equilibria and Structural Polymorphism of Lipids.- 5. Physicochemical Properties of the Polar Lipids in A. laidlawii.- 6. Regulation of the Membrane Lipid Composition.- 7. Physicochemical Interpretations of the Lipid Regulation Mechanisms.- 8. References.- 5 The Role of Cholesterol in Mycoplasma Membranes.- 1. Introduction.- 2. Mode of Sterol Uptake.- 3. Sterol Structure-Function Relationships.- 4. Sterol-Mediated Regulation.- 5. Concluding Remarks.- 6. References.- 6 Extramembranous Structure in Mycoplasmas.- 1. Introduction.- 2. Morphology and Electron Microscopy.- 3. Capsule Composition and Chemical Structure.- 4. Biological and Pathogenic Characteristics of Capsule.- 5. Concluding Remarks.- 6. References.- 7 Spiralins.- 1. Definition.- 2. Localization of Spiralin in Spiroplasma Cells.- 3. Properties of Spiralin as Deduced from Studies of the Protein.- 4. Properties of Spiralin as Deduced from Its Gene.- 5. Secondary Structure and Topology of Spiralin in the Spiroplasma Membrane.- 6. Spiralin and Prespiralin.- 7. Polymorphism of Spiralin.- 8. Spiralins in Spiroplasma Species Other Than S. citri and S. melliferum.- 9. Conclusion.- 10. References.- 8 Adherence of Mycoplasma to Cell Surfaces.- 1. Introduction.- 2. Morphological Studies.- 3. Adherence: The Molecular Aspects.- 4. The Mollicutes Counterparts: Adhesins.- 5. Molecular Arrangement of Adhesins in the Membrane and the Possible Role of the Cytoskeleton and Phosphorylated Proteins.- 6. The Advantage of Adherence to Mollicutes.- 7. Concluding Remarks.- 8. References.- 9 The Cytadhesins of Mycoplasma pneumoniae and M. genitalium.- 1. Introduction.- 2. Identification of Protein Adhesins of M. pneumoniae.- 3. Isolation of Cytadherence-Deficient M. pneumoniae Mutants.- 4. Characterization of the P1 Adhesin Gene of M. pneumoniae.- 5. Multicopy Nature and Sequence Divergency of the P1 Gene.- 6. Characterization of the 30-kDa Adhesin (P30) Gene of M. pneumoniae.- 7. The P1-Analogue Adhesin of M. genitalium.- 8. Characterization of Gene and Protein Sequence Homologies between the P140 Adhesins of M. genitalium and the P1 Adhesin of M. pneumoniae.- 9. References.- 10 Ion Pumps and Volume Regulation in Mycoplasmas.- 1. Introduction.- 2. Primary Ion Transport Systems.- 3. Secondary Ion Transport Systems.- 4. Electrochemical Potentials in Mycoplasmas.- 5. Volume Regulation.- 6. Concluding Remarks.- 7. References.- 11 Transport Systems in Mycoplasmas.- 1. Introduction.- 2. The Permeability Barrier.- 3. Sugar Transport.- 4. Amino Acid Transport.- 5. Fatty Acid Transport.- 6.Conclusions.- 7. References.