Membrane Interactions of Fusogenic Coiled-Coil Peptides: Implications for Lipopeptide Mediated Vesicle Fusion

Abstract

Fusion of lipid membranes is an important natural process for the intra- and intercellular exchange of molecules. However, little is known about the actual fusion mechanism at the molecular level. In this study we examine a system that models the key features of this process. For the molecular recognition between opposing membranes two membrane anchored heterodimer coiled-coil forming peptides called 'E' (EIAALEK)3 and 'K' (KIAALKE)3 were used. Lipid monolayers and IR reflection absorption spectroscopy (IRRAS) revealed the interactions of the peptides 'E', 'K', and their parallel coiled-coil complex 'E/K' with the phospholipid membranes and thereby mimicked the pre- and postfusion states, respectively. The peptides adopted α-helical structures and were incorporated into the monolayers with parallel orientation. The strength of binding to the monolayer differed for the peptides and tethering them to the membrane increased the interactions even further. Remarkably, these interactions played a role even in the postfusion state. These findings shed light on important mechanistic details of the membrane fusion process in this model system. Furthermore, their implications will help to improve the rational design of new artificial membrane fusion systems, which have a wide range of potential applications in supramolecular chemistry and biomedicine.

A Coiled-Coil Peptide Shaping Lipid Bilayers upon Fusion

“…Apparently, the tethered peptide in LPK* is bound stronger to the vesicle than the untethered K*. Similar effects were also observed earlier in a study of the interactions of K, E, LPK, and LPE with lipid monolayers (19).…”

“…Recent infrared spectroscopic studies of LPE and LPK containing lipid mono-or bilayers revealed differing behaviors of the two peptides before the fusion commences (19,20). The negatively charged E shows relatively weak interactions with the lipid interface, staying in the water phase in the form of homomeric coiled-coil dimers E/E.…”

“…It was hypothesized that the direct K-membrane interactions lead to distortion of the bilayers or increased local curvature and thereby promote the merging of lipid bilayers (19,20). In this model the two peptides E and K have different functions apart from coiled-coil formation, leaving multiple tasks to K. However, very little is known about the structural consequences of the insertion of the amphipathic helix of K into lipid membranes.…”

Computational insight in the role of fusogenic lipopeptides at the onset of liposome fusion

“…No disattachment was observed in the additional 2.2 μs following peptide insertion. This positioning, somehow expected due to the amphipathic character of the peptide, has been reported in previous atomistic simulations of very similar fusion peptides (influenza hemagglutinin) [19] and determined by InfraRed Reflection Absorption Spectroscopy (IRRAS) measurements for LP 12 K and LP 12 E in mono-layers with an identical lipid/cholesterol composition [20].…”

“…This criterion is based on the concept that homomers do not play a role in fusion, meaning that their formation should be avoided. Nevertheless, there is ample experimental evidence that such aggregates do form [15,20]. The considered solitary lipopeptides thus represent a limiting case, quantified by the number of anchors n a = 1, and it is relevant to consider the situation n a N 1, i.e.…”