Membrane Fusion

Abstract

The sections in this article are: Observation of Fusion Requires Physical Techniques for Monitoring Mixing of Membranes and the Compartments they Enclose Morphological Changes Following Fusion Are Observed by Light Microscopy but Membrane Fusion May Occur without such Changes Fluorescence Microscopy and Spectrofluorometry Allow Quantitation of Membrane Fusion Events in Living Cells Electron Microscopy Provides Direct Observation of Structural Rearrangements Due to Fusion Patch‐Clamp Techniques Allow the Monitoring of Very Fast Openings of Fusion Pores What Do We Learn from “Nonbiological” Fusion Processes? Ca 2+ Induces Aggregation Destabilization, and Fusion of Liposomes Containing Phospholipids with Negatively Charged Head‐groups Fusion of Lipid Membranes by Amphipathic and Nonpolar Molecules Correlates with Their Lytic and Aggregational Activity Dehydration, Aggregation, and Destabilization of Membranes by Polyethelene Glycol Are Essential for Fusion of Lipid Membranes Destabilization by High‐Voltage Electric Pulses Leads to Fusion of Adjoining Membranes Molecular Rearrangements in the Lipid Bilayers during the Very Act of Fusion May Involve Intermediate Structures Specialized Proteins Mediate Fusion in Life Processes Viral Envelope Proteins Contain Hydrophobic “Fusion Peptide” Sequences To Enter a Cell a Virus Must Find the Receptor That Invites It In Some Viruses Require More Than One Type of Envelope Protein for Entry Influenza Hemagglutinin Was the Only Fusion Protein with Known Three‐Dimensional Structure The Process of HA ‐mediated Membrane Fusion Can Be Dissected into a Number of Elementary Steps Human Immunodeficiency Virus Type 1 ( HIV ‐1), the Primary Etiological Agent of the Acquired Immunodeficiency Syndrome ( AIDS ), Enters Cells by Membrane Fusion at Neutral pH The Receptor CD 4 Plays Both a Passive and an Active Role in Allowing Entry of the Virus into the Cell Stable Envelope Glycoprotein‐Receptor Complex Formation Is Rate‐limiting in the Overall Fusion Process Multiple Copies of the HIV ‐1 Envelope Glycoprotein May Be Required for Fusion Pore Formation Sperm Membrane Proteins Involved in Sperm‐Egg Fusion May Resemble Viral Fusion Proteins Toward A Resolution of Fusion Proteins in Exocytosis Multiple Proteins May Be Required for Intracellular Fusion Toward A Physicochemical Analysis of Fusion Kinetics Delays in Fusion Are Proportional to the Fusion Barriers and Decrease with an Increase in the Strength of the Fusogen Rates of Fusion Can Provide Information for the Time Course of Membrane Merging and Fusion Pore Expansion Fusion Yields and Delays Are Related but May Reflect Different Properties of the Fusing Membranes Does Understanding Membrane Fusion Need New Breakthroughs in Methodology? Note Added in Proof

The role of transmembrane domains in membrane fusion

“…Virus docking to cellular membranes involves exposition of the amphipathic fusion peptides by a conformational change of ectodomains; this is followed by fusion peptide insertion into the target bilayer. Subsequent structural rearrangements of the ectodomains are probably required to closely juxtapose both bilayers [1,12,35] (Fig. 1a).…”

“…Several excellent recent reviews cover the mechanism of fusion [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17]. Depending on the perspective of the different authors, these reviews emphasize different aspects of fusion, like the specificity of membranemembrane recognition prior to fusion, regulation of fusogenic proteins by accessory factors and the biophysics of bilayer mixing, to name a few.…”

“…Functional dissection of the fusion reaction is primarily based on two major model systems. One system comprises envelope proteins from different viruses, of which the trimeric class I fusion protein influenza hemagglutinin (HA) represents the most thoroughly investigated case [2,12]. Class I viral fusogens are synthesized as precursor molecules that are proteolytically cleaved to yield the mature forms.…”

Temperature dependence and resonance assignment of 13C NMR spectra of selectively and uniformly labeled fusion peptides associated with membranes

“…1 H decoupling was applied during pulses and detection. The 15 N pulse length was set by minimization of S 1 signals for the model compound and the TPPM pulse length was set by maximization of the S 0 signal for the model compound.…”

Many mechanisms, one entrance: membrane protein translocation into the nucleus

“…These events are energy-, temperature-and calcium-dependent (reviewed in [5][6][7]). Fusion events in these membrane compartments have been also linked to specific proteins that promote vesicle fusion such as SNAREs and NSF.…”