Mechanosensitive Ion Channels, Part A (eBook)

Cover 1
Contents 6
Contributors 12
Foreword 16
Previous Volumes in Series 18
Chapter 1: Structures of the Prokaryotic Mechanosensitive Channels MscL and MscS 21
I. Overview 21
II. Introduction 22
III. Conductances of MscL and MscS: General Considerations 23
IV. Structure Determination of MscL and MscS 26
A. General Considerations in Membrane Protein Crystallography 26
B. Crystallographic Analysis of MscL and MscS 29
V. MscL and MscS Structures 31
VI. The Permeation Pathway in MscL and MscS 35
VII. Disulfide Bond Formation in MscL 37
VIII. Concluding Remarks 38
Acknowledgments 40
References 40
Chapter 2: 3.5 Billion Years of Mechanosensory Transduction: Structure and Function of Mechanosensitive Channels in Prokaryotes 45
I. Overview 46
II. Introduction 46
III. Discovery, Mechanism, and Structure of MS Channels in Prokaryotes 48
A. Historical Perspective 48
B. Conductance, Selectivity, and Activation by Membrane Tension of Bacterial MS Channels 48
C. Cloning of MscL and MscS of E. coli 50
D. Molecular Identification of MS Channels in Archaea 53
E. Molecular Structure of Prokaryotic MS Channels 55
F. Bilayer Mechanism and Gating by Mechanical Force 59
G. Spectroscopic Studies 61
H. Structural Models of Gating in MscL and MscS 63
IV. Pharmacology of Prokaryotic MS Channels 64
V. Families of Prokaryotic MS Channels 65
A. MscL Family 66
B. MscS Family 66
VI. Early Origins of Mechanosensory Transduction 66
A. Physiological Function of MS Channels in Prokaryotic Cells 67
B. Function of MscS-Like Channels in Mechanosensory Transduction in Plants 69
VII. Concluding Remarks 70
Acknowledgments 70
References 70
Chapter 3: Activation of Mechanosensitive Ion Channels by Forces Transmitted Through Integrins and the Cytoskeleton 79
I. Overview 79
II. Introduction 80
III. Conventional Views of MS Channel Gating 83
IV. Tensegrity-Based Cellular Mechanotransduction 86
V. Force Transmission Through Integrins in Living Cells 90
VI. Potential Linkages Between Integrins and MS Ion Channels 93
VII. Conclusions and Future Implications 97
References 98
Chapter 4: Thermodynamics of Mechanosensitivity 107
I. Overview 107
II. Introduction 108
A. General Equations 110
III. Area Sensitivity 111
A. Line Tension and Area Sensitivity 113
B. Direct Observations of the Effect of Line Tension and Shape Transformation 116
IV. Shape Sensitivity 119
A. Experimental Observation of Shape Sensitivity 120
V. Length Sensitivity and Switch Between Stretch-Activation and Stretch-Inactivation Modes 123
A. Channel Activation by LPLs 128
B. Other Parameters Regulating Switch Between Stretch-Activation and Inactivation Modes 131
VI. Thermodynamic Approach and Detailed Mechanical Models of MS Channels 132
A. Detailed Mechanical Models 133
VII. Conclusions 134
References 135
Chapter 5: Flexoelectricity and Mechanotransduction 141
I. Overview 141
II. Introduction 141
III. Flexoelectricity, Membrane Curvature, and Polarization 142
A. Flexoelectricity and Membrane Lipids 144
B. Flexoelectricity and Membrane Proteins 150
IV. Experimental Results on Flexoelectricity in Biomembranes 151
A. Theoretical Remarks 151
B. Experimental Data 152
V. Flexoelectricity and Mechanotransduction 163
VI. Conclusions 167
References 168
Chapter 6: Lipid Effects on Mechanosensitive Channels 171
I. Overview 171
II. Intrinsic Membrane Proteins 172
III. Effects of Lipid Structure on Membrane Protein Function 172
IV. How to Explain Effects of Lipid Structure on Membrane Protein Function 175
A. The Lipid Annulus 175
B. The Fluidity of a Lipid Bilayer and Its Consequences 176
C. The Importance of Hydrophobic Thickness 183
D. Curvature Stress 186
E. Elastic Strain and Pressure Profiles 188
F. General Features of Lipid-Protein Interactions 190
V. What Do These General Principles Tell Us About MscL? 191
References 194
Chapter 7: Functional Interactions of the Extracellular Matrix with Mechanosensitive Channels 199
I. Overview 199
II. Mechanotransduction 200
III. Mechanosensitive Channels in Connective Tissue Cells 202
IV. The Extracellular Environment of Cells 204
V. Force Transmission from Matrix to Cytoskeleton 207
A. Focal Adhesions 207
B. Selectins 208
VI. Experimental Models of Force Application to Connective Tissue Cells 209
VII. Effects of Force on Cell Surface Structures 213
VIII. Future Approaches 214
References 215
Chapter 8: MscL: The Bacterial Mechanosensitive Channel of Large Conductance 221
I. Overview 222
II. Introduction and Historical Perspective 222
A. The Discovery of MS Channels in Bacteria 222
B. Proposing a Function 223
C. The Identification of Multiple MS Channel Activities in E. coli 223
D. Identification of the E. coli mscL Gene 225
E. Early Mutagenesis Studies 226
III. A Detailed Structural Model: An X-Ray Crystallographic Structure from an E.coli MscL Orthologue 227
A. The Crystal Structure 228
B. Fitting the Structure with the Findings from Mutagenesis Studies 229
C. Comparing Tb-MscL with Eco-MscL 230
IV. Proposed Models for How the MscL Channel Opens 232
A. Opening the Channel: Twist and Turn 232
B. Molecular Dynamic Simulations 242
V. Physical Cues for MscL Channel Gating: Protein-Lipid Interactions 243
A. Studies of the Energetic and Spatial Parameters for MscL Gating 243
B. Does MscL Sense the Pressure Across the Membrane or the Tension Within It? 244
C. Sensing the Biophysical Properties of the Membrane 244
D. Specific Protein-Lipid Interactions 245
VI. MscL as a Possible Nanosensor 247
VII. Conclusions 248
Acknowledgments 248
References 249
Chapter 9: The Bacterial Mechanosensitive Channel MscS: Emerging Principles of Gating and Modulation 255
I. Overview 256
II. Introduction 256
III. MscS and Its Relatives 258
A. A Brief Account of Bacterial Osmoregulation and the Discovery of MscS 258
B. MscS Vs MscK: How to Interpret Early Functional Data? 260
C. Purification and Reconstitution of MscS Showed Homo-Multimeric Channels Activated by Tension in the Lipid Bilayer 262
IV. Structural and Computational Studies 262
A. Structure of MscS and First Hypotheses About Its Gating Mechanism 262
B. Computational Studies of MscS 264
V. Functional Properties of MscS 269
A. MscS Conduction and Selectivity 269
B. Gating Characteristics of MscS In Situ 270
C. Mutations That Affect MscS Activity 272
D. MscS Inactivation 273
VI. What Do the Closed, Open, and Inactivated States of MscS Look Like? 276
A. Is the Crystal Structure a Native State? 277
B. Closed State 278
C. Open State 278
VII. Emerging Principles of MscS Gating and Regulation and the New Directions 280
References 283
Chapter 10: StructureFunction Relations of MscS 289
I. Overview 289
II. Introduction 290
A. Functional Overview 293
III. The Structure of MscS 296
A. The Membrance Domain 298
B. The Cytoplasmic Domain 298
C. Variations in Structure 299
D. Twisting MscS Around the Pore 300
E. MscS Is Small but Beautifully Formed 301
IV. MscS Mutational Analysis 302
V. Structural Transitions in MscS 304
A. The Need for the Closed State 304
B. The Crystal State 305
C. The TM3 Pore 307
D. The Closed-to-Open Transition 308
VI. Conclusions and Future Perspective 311
Acknowledgments 311
References 312
Chapter 11: The MscS Cytoplasmic Domain and Its Conformational Changes on the Channel Gating 315
I. Overview 315
II. MscL and MscS: Primary Gates and Similarities in Activation 316
III. The MscL Cytoplasmic Regions and Functioning of the Channel 319
IV. The MscS C-Terminal Chamber: The Cage-Like Structure and Kinetics 320
V. Structural Alterations of the MscS Cytoplasmic Chamber on Gating 323
VI. Conclusions and Perspectives 325
Acknowledgments 326
References 326
Chapter 12: Microbial TRP Channels and Their Mechanosensitivity 331
I. Overview 331
II. A History TRP-Channel Research 332
III. The Mechanosensitivity of Animal TRP Channels 333
IV. Distribution and the Unknown Origin of TRPs 334
V. TRPY1: The TRP Channel of Budding Yeast 337
VI. Other Fungal TRP Homologues 341
VII. Sequence Information Does Not Explain TRP Mechanosensitivity 342
VIII. Conclusions 343
Acknowledgment 344
References 344
Chapter 13: MscS-Like Proteins in Plants 349
I. Overview 349
II. Mechanosensation and Ion Channels in Plants 350
A. Plants Cells and Turgor Pressure 350
B. Mechanosensory Signal Transduction in Plants 351
C. MS Ion are Present in Plant Cell Membranes 353
III. The Eukaryotic Family of MscS_Like Proteins 357
A. E. coil MscS 357
B. The Eukaryotic Subfamily 359
IV. The Arabidopsis MSL Genes 365
A.Overview 365
B. Subcellular Localization of MSL Proteins 367
C. Control of MSL Gene Expression 368
D. MSL2, MSL3, and the Control of Organelle Morphology 369
V. Outstanding Questions 371
A. How Have MscS-Like Proteins Evolved? 371
B. What Roles Do MS Ion Channels Play in Plant Biology? 371
C. Is Clustering of MS Ion Channels Important? 372
V. Conculsion 373
References 373
Chapter 14: Delivering Force and Amplifying Signals in Plant Mechanosensing 381
I. Overview 382
II. Introduction 382
III. Focusing Force 385
A. Force Experienced by a Plant Is Chiefly Borne by the Heterogeneous Wall System 385
B. The Plasmalemmal Reticulum Carries Force to the Channels 386
C. Implication of Heterogeneous Walls for Thigmotropic Reception 392
D. Walls Are Only Half the Mechanical Story: Gravitropism, Like Plant Form, Depends on Force Generated Inside Cells 392
E. Not Just Any Displacement Triggers Gravitropism 396
F. Map of Mechanotropic Cells in the Root Cap 396
IV. Transduction and Ensuing Events in Thigmotropism 398
V. Early Events in Gravitropism 399
A. Direct Evidence for Pulsed Ca2+ Elevation 399
B. Curvature Kinetics Are Consistent with MCaCs as Gravitropic Transducers 400
C. Ca2+ Kinetics and Xenobiotic Effects Are Consistent with MCaCs as Gravitropic Transducers 401
D. Ramping Sensitivity Up and Down Again: Voltage and pH Modulation of MCaCs 403
E. Variable Linkage: A "Nonmechanical" Role for the PR 404
F. Cloistering Ca2+ 404
VI. From Primary Transduction Pulse Forward: Facilitative and Vectorial Gravitropic Reception 405
A. Facilitative Gravitropic Reception 406
B. Vectorial Gravitropic Reception 406
C. Decay of Facilitative Reception 408
VII. What Comes Next 409
References 410
Chapter 15: MS Channels in Tip-Growing Systems 413
I. Overview 413
II. Introduction 414
III. Lilium longiflorum Pollen Tubes 415
IV. Saprolegnia ferax Hyphae 420
V. Silvetia compressa Rhizoids 422
VI. Neurospora crassa Hyphae 425
VII. Is Turgor Necessary for Activation of MS Channels? 426
VIII. Conclusions 427
References 429
Index 433