Peptides and Membrane Fusion: Towards an Understanding of the Molecular Mechanism of Protein-Induced Fusion

Abstract

Processes such as endo- or exocytosis, membrane recycling, fertilization and enveloped viruses infection require one or more critical membrane fusion reactions. A key feature in viral and cellular fusion phenomena is the involvement of specific fusion proteins. Among the few well-characterized fusion proteins are viral spike glycoproteins responsible for penetration of enveloped viruses into their host cells, and sperm proteins involved in sperm-egg fusion. In their sequences, these proteins possess a "fusion peptide, " a short segment (up to 20 amino acids) of relatively hydrophobic residues, commonly found in a membrane-anchored polypeptide chain. To simulate protein-mediated fusion, many studies on peptide-induced membrane fusion have been conducted on model membranes such as liposomes and have employed synthetic peptides corresponding to the putative fusion sequences of viral proteins, or de novo synthesized peptides. Here, the application of peptides as a model system to understand the molecular details of membrane fusion will be discussed in detail. Data obtained from these studies will be correlated to biological studies, in particular those that involve viral and sperm-egg systems. Structure-function relationships will be revealed, particularly in the context of protein-induced membrane perturbations and bilayer-to-nonbilayer transition underlying the mechanism of fusion. We will also focus on the involvement of lipid composition of membranes as a potential regulating factor of the topological fusion site in biological systems.

Synthesis, Enhanced Fusogenicity, and Solid State NMR Measurements of Cross-Linked HIV-1 Fusion Peptides

“…Spacers were placed in the 6-mm rotor so that the sample was restricted to the central 2/3 of the coil length (160 µL volume), and the 13 C and 15 N RF fields were reduced by at most 10% from their maximum values in the rotor center. The NMR detection channel was tuned to 13 C at 100.8 MHz, the decoupling channel was tuned to 1 H at 400.8 MHz, and the third channel was tuned to 15 N at 40.6 MHz. Experiments were carried out using a MAS frequency of 8000 Hz that was stabilized to (2 Hz.…”

“…A single 50-kHz 13 C refocusing π pulse was placed at the center of the dephasing time, and 1 H TPPM decoupling of 65 kHz was applied during both dephasing and detection (64). The 13 C transmitter frequency was set to 155 ppm, and the 15 15 N π pulse at the middle and end of each rotor period, while the S 0 acquisition did not contain these pulses. XY-8 phase cycling was used for the 15 N pulses (65,66).…”

“…The 13 C transmitter frequency was set to 155 ppm, and the 15 15 N π pulse at the middle and end of each rotor period, while the S 0 acquisition did not contain these pulses. XY-8 phase cycling was used for the 15 N pulses (65,66). During the dephasing period, pulses were not actively synchronized to the rotor phase.…”

“…The free peptide causes fusion of liposomes and erythrocytes, and numerous mutational studies have shown strong correlations between fusion peptide-induced liposome fusion and viral/host cell fusion (5,(11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25).…”

Peptide Mimics of the Vesicular Stomatitis Virus G-protein Transmembrane Segment Drive Membrane Fusion in Vitro

“…Synthetic versions of many of these soluble fusion peptides drive liposome-liposome fusion in vitro. Furthermore, the fusogenic function of some synthetic fusion peptides is sensitive to point mutations in a similar fashion as the corresponding fulllength fusion proteins (2,5,6). Therefore, they appear to be partially independent functional domains whose interaction with target membranes is an early event initiating fusion.…”