A strong correlation between fusogenicity and membrane insertion depth of the HIV fusion peptide

Membrane fusion is required for diverse biological functions ranging from viral infection to neurotransmitter release. Fusogenic proteins increase the intrinsically slow rate of fusion by coupling energetically downhill conformational changes of the protein to kinetically unfavorable fusion of the membrane-phospholipid bilayers. Class I viral fusogenic proteins have an N-terminal hydrophobic fusion peptide (FP) domain, important for interaction with the target membrane, plus a C-terminal transmembrane (C-term-TM) helical membrane anchor. The role of the water-soluble regions of fusogenic proteins has been extensively studied, but the contributions of the membrane-interacting FP and C-term-TM peptides are less well characterized. Typically, FPs are thought to bind to membranes at an angle that allows helix penetration but not traversal of the lipid bilayer. Here, we show that the FP from the paramyxovirus parainfluenza virus 5 fusogenic protein, F, forms an N-terminal TM helix, which self-associates into a hexameric bundle. This FP also interacts strongly with the C-term-TM helix. Thus, the fusogenic F protein resembles SNARE proteins involved in vesicle fusion by having water-soluble coiled coils that zipper during fusion and TM helices in both membranes. By analogy to mechanosensitive channels, the force associated with zippering of the water-soluble coiled-coil domain is expected to lead to tilting of the FP helices, promoting interaction with the C-term-TM helices. The energetically unfavorable dehydration of lipid headgroups of opposing bilayers is compensated by thermodynamically favorable interactions between the FP and C-term-TM helices as the coiled coils zipper into the membrane phase, leading to a pore lined by both lipid and protein.T he basic mechanisms of viral membrane fusion have been studied extensively, but major gaps remain in our understanding of the relative roles of lipidic intermediates and viral fusogenic proteins in lowering the energy barrier for the overall process (1-4). The most common mechanistic hypothesis concerning enveloped viral fusion is that fusogenic proteins primarily serve to bring the target cell and viral membranes into proximity. Fusion occurs in a multistep process, in which the virus first binds to a specific receptor; this event and/or other environmental cues then cause a conformational change in the protein, leading to a metastable state with an exposed hydrophobic fusion peptide (FP) that binds to the target membrane. Once engaged with the bilayer, a second energetically favorable conformational change in the fusogenic protein then exerts a force pulling the FP toward the viral membrane, in effect reeling the host and viral membranes together.The conformational changes involved in the water-soluble portions of viral fusogenic proteins have been largely elucidated, but the roles of the membrane-binding FP and the C-terminal transmembrane (C-term-TM) anchor are less clear. After the crystal structure of the prefusogenic form of influenza hemagglutinin (HA) was solved...

Section: Discussionmentioning

confidence: 99%

Transmembrane orientation and possible role of the fusogenic peptide from parainfluenza virus 5 (PIV5) in promoting fusion

Donald¹,

Zhang

Fiorin

et al. 2011

“…In this report, we describe a previously unidentified structure-motivated mechanism by which SpoVM discriminates between differently curved membrane surfaces. Current understanding of membrane curvature sensing mainly comes from the study of the recognition of highly curved membranes, such as those formed by ∼50 nm-diameter vesicles (28,38,(41)(42)(43). In those scenarios, the prevailing model for curvature recognition is based on the premise that highly curved surfaces provide more binding sites for curvature-recognizing proteins, presumably because acute membrane curvature drives phospholipid head groups in the outer leaflet apart, and increases the occurrences of packing defects that are manifested near the surface of the membrane (26,28) (Fig.…”

Section: Discussionmentioning

confidence: 99%

Structural basis for the geometry-driven localization of a small protein

Gill

Castaing

Hsin

et al. 2015

In bacteria, certain shape-sensing proteins localize to differently curved membranes. During sporulation in Bacillus subtilis, the only convex (positively curved) surface in the cell is the forespore, an approximately spherical internal organelle. Previously, we demonstrated that SpoVM localizes to the forespore by preferentially adsorbing onto slightly convex membranes. Here, we used NMR and molecular dynamics simulations of SpoVM and a localization mutant (SpoVM P9A ) to reveal that SpoVM's atypical amphipathic α-helix inserts deeply into the membrane and interacts extensively with acyl chains to sense packing differences in differently curved membranes. Based on binding to spherical supported lipid bilayers and Monte Carlo simulations, we hypothesize that SpoVM's membrane insertion, along with potential cooperative interactions with other SpoVM molecules in the lipid bilayer, drives its preferential localization onto slightly convex membranes. Such a mechanism, which is distinct from that used by high curvature-sensing proteins, may be widely conserved for the localization of proteins onto the surface of cellular organelles.ArfGAP1 | SpoIVA | DivIVA | curvature sensing | lipid packing

“…Extensive spectroscopic studies have shown that influenza, HIV, and paramyxovirus FPs are conformationally plastic and adopt a partially inserted topology in the membrane to induce nonlamellar structures (7)(8)(9)(10)(11). In comparison, little is known about the structures of the C-terminal TMD of viral fusion proteins.…”

mentioning

confidence: 99%

Viral fusion protein transmembrane domain adopts β-strand structure to facilitate membrane topological changes for virus–cell fusion

Yao

Lee

Waring

et al. 2015

The C-terminal transmembrane domain (TMD) of viral fusion proteins such as HIV gp41 and influenza hemagglutinin (HA) is traditionally viewed as a passive α-helical anchor of the protein to the virus envelope during its merger with the cell membrane. The conformation, dynamics, and lipid interaction of these fusion protein TMDs have so far eluded high-resolution structure characterization because of their highly hydrophobic nature. Using magicangle-spinning solid-state NMR spectroscopy, we show that the TMD of the parainfluenza virus 5 (PIV5) fusion protein adopts lipid-dependent conformations and interactions with the membrane and water. In phosphatidylcholine (PC) and phosphatidylglycerol (PG) membranes, the TMD is predominantly α-helical, but in phosphatidylethanolamine (PE) membranes, the TMD changes significantly to the β-strand conformation. Measured order parameters indicate that the strand segments are immobilized and thus oligomerized. 31 P NMR spectra and small-angle X-ray scattering (SAXS) data show that this β-strand-rich conformation converts the PE membrane to a bicontinuous cubic phase, which is rich in negative Gaussian curvature that is characteristic of hemifusion intermediates and fusion pores. 1 H-31 P 2D correlation spectra and 2 H spectra show that the PE membrane with or without the TMD is much less hydrated than PC and PG membranes, suggesting that the TMD works with the natural dehydration tendency of PE to facilitate membrane merger. These results suggest a new viral-fusion model in which the TMD actively promotes membrane topological changes during fusion using the β-strand as the fusogenic conformation.solid-state NMR spectroscopy | small-angle X-ray scattering | conformational polymorphism | membrane curvature | peptide-membrane interactions V iral fusion proteins mediate entry of enveloped viruses into cells by merging the viral lipid envelope and the cell membrane. The membrane-interacting subunit of these glycoproteins contains two hydrophobic domains: a fusion peptide (FP) that is usually located at the N terminus and a transmembrane domain (TMD) at the C terminus (1). Together, these domains sandwich a water-soluble ectodomain with a helical segment that trimerizes into a coiled coil. During virus-cell fusion, the trimeric protein, which initially adopts a compact structure, unfolds to an extended intermediate that exposes the FP to the target cell membrane while keeping the TMD in the virus envelope. This extended conformation then folds onto itself to form a trimer of hairpins, in so doing pulling the cell membrane and the virus envelope into close proximity (2, 3). Subsequently, the FP and TMD are hypothesized to deform the two membranes and dehydrate them (4), eventually causing a fusion pore and a fully merged membrane. In the postfusion state, most viral fusion proteins exhibit a six-helixbundle structure in the ectodomain due to the trimer of hairpins (5).This model of virus-cell fusion largely derives from crystal structures of fusion proteins in the pre-and postfusion st...