Characterization of the Sequence of Interactions of the Fusion Domain of the Simian Immunodeficiency Virus with Membranes

Abstract

The simian immunodeficiency virus fusion peptide constitutes a 12-residue N-terminal segment of the gp32 protein that is involved in the fusion between the viral and cellular membranes, facilitating the penetration of the virus in the host cell. Simian immunodeficiency virus fusion peptide is a hydrophobic peptide that in Me 2 SO forms aggregates that contain ␤-sheet pleated structures. When added to aqueous media the peptide forms large colloidal aggregates. In the presence of lipidic membranes, however, the peptide interacts with the membranes and causes small changes of the membrane electrostatic potential as shown by fluorescein phosphatidylethanolamine fluorescence. Thioflavin T fluorescence and Fourier transformed infrared spectroscopy measurements reveal that the interaction of the peptide with the membrane bilayer results in complete disassembly of the aggregates originating from an Me 2 SO stock solution. Above a lipid/peptide ratio of about 5, the membrane disaggregation and water precipitation processes become dependent on the absolute peptide concentration rather than on the lipid/peptide ratio. A schematic mechanism is proposed, which sheds light on how peptide-peptide interactions can be favored with respect to peptide-lipid interactions at various lipid/peptide ratios. These studies are augmented by the use of the fluorescent dye 1-(3-sulfonatopropyl)-4-[␤[2-(di-n-octylamino)-6-naphthyl]vinyl] pyridinium betaine that shows the interaction of the peptide with the membranes has a clear effect on the magnitude of the so-called dipole potential that arises from dipolar groups located on the lipid molecules and oriented water molecules at the membrane-water interface. It is shown that the variation of the membrane dipole potential affects the extent of the membrane fusion caused by the peptide and implicates the dipolar properties of membranes in their fusion.

A virtual instrumentation based protocol for the automated implementation of the inner field compensation method

“…A reasonable explanation for this phenomenon was based on the assertion that gramicidin reduces the existing positive dipole potential of monolayers and bilayers by inducing reorientation of dipole-carrying groups. Such a possibility has also been brought forward by other previous data, leading to the conclusion that the molecular mechanisms by which the binding of the peptide to the membrane affects the dipole potential, indicates the possible arrangements of membrane dipoles as well as the peptide helical dipole vectors [12]. Further experiments will be needed to elucidate intricacies of electric interactions that manifest between lipid membranes and ion-channel forming peptides, which seem to bi-univocally modulate each other's physical manifestations.…”

“…The dipole potential has been shown to play an important role for proteins insertion and functioning [7], kinetics of the gramicidin channel (8), modulation of the activity of phospholipase A2 [9] and electrical conductance of certain aqueous protein pores [10]. Moreover, dipole potential was shown to affect the membrane insertion and folding of a model amphiphilic peptide [11], as well as the extent of the membrane fusion [12]. More interestingly, studies undertaken on peptides and proteins embedded on membranes with various compositions illustrated the interplay between the structure, dynamics, and function of such macromolecules and the properties of the lipid membrane.…”

Effects of the Membrane Dipole Potential on the Interaction of Saquinavir with Phospholipid Membranes and Plasma Membrane Receptors of Caco-2 Cells

“…The dual-wavelength ratiometric method complements the FPE-based technique as it facilitates the measurement of the membrane interactions of uncharged molecules (7,8). The monitoring of the membrane dipole potential as a means to determine intermolecular interactions, however, has been used mainly with model membrane systems, and apart from a pilot study published from our laboratory (10), no comprehensive studies have been reported with living cells.…”

“…In the present paper, therefore, we demonstrate the possibility of using both FPE and di-8-ANEPPS in a complementary way with model membranes and with living cells with a view to revealing the role of the membrane dipole potential in affecting important cellular processes. In model membrane systems the capacity of sterols such as cholesterol and 6-ketocholestanol to affect the magnitude of the membrane dipole potential is well established (7,8,11,12). On the other hand, cholesterol is an important component of the membrane lipid domains known as "rafts" (13,14), and removal of cholesterol from cellular membranes following treatment with cyclodextrins or alteration of its behavior by utilizing filipin, amphotericin, and other compounds has been widely reported as a useful method to disrupt "detergent-resistant" membrane microdomains (14 -16).…”

“…Recent studies implicate the dipole potential in the interactions of a number of different molecular species with membranes, such as gramicidin (3,4), phospholipase A (5), signal sequences (6,7), and fusion peptides (8).…”