Membrane Interaction and Conformational Properties of the Putative Fusion Peptide of PH-30, a Protein Active in Sperm-Egg Fusion

Abstract

A peptide representing the putative fusion domain of PH-30, a sperm surface protein involved in sperm-egg fusion, was synthesized, and its interaction with model lipid membranes was characterized by biophysical methods. While the peptide binds to the vesicles composed of both neutral and acidic lipids, the apparent affinity is significantly higher for the latter lipid class. The intervesicular lipid mixing assay suggests that the synthetic peptide is able to induce fusion of large unilamellar vesicles. Circular dichroism and Fourier-transform infrared spectroscopy show that while in an aqueous buffer the peptide exists in an essentially unordered conformation, binding to the membranes results in a conformational transition to a @-structure. These data indicate that the fragment identified on the a-subunit of PH-30 as a putative fusion peptide is indeed a good candidate for this role. However, in contrast to what has been proposed for some viral fusion peptides, the PH-30 fusion domain is highly unlikely to act as an insertional "sided" helix.

A soluble peripherin/Rds C-terminal polypeptide promotes membrane fusion and changes conformation upon membrane association

“…Structural changes within fusion proteins are required to allow a fusion protein to go from the prefusion to the fusion competent state and to mediate the formation of a fusion pore (Mellman, 1995;Pecheur et al, 1999;Bentz, 2000). Peptide-modeling studies suggest that sperm fertilin α (Muga et al, 1994), measles virus F1 (Epand et al, 1992) and the S protein from hepatitis B virus (Rodriguez-Crespo et al, 1995;Rodriguez-Crespo et al, 1996) adopt a β-sheet structure in a lipid environment (Pecheur et al, 1999). Alternatively at higher lipid-toprotein ratios fertilin has been shown to prefer an α-helical conformation with a helix that inserts obliquely into the membrane bilayer, a topology that requires the presence of negatively charged lipids (Martin et al, 1998).…”

The Central Proline of an Internal Viral Fusion Peptide Serves Two Important Roles

“…Membrane interactions of synthetic peptides representing the candidate internal fusion peptides of Ebola virus G2 and guinea pig fertilin ␣ have been reported (36,38,44). In each case, the peptides preferentially interacted with acidic phospholipid bilayers.…”

Membrane Fusion Is Induced by a Distinct Peptide Sequence of the Sea Urchin Fertilization Protein Bindin

“…Indeed, B18 tends to assume a partially ␣-helical conformation in the presence of Zn 2ϩ , at least in the aqueous environment where we could study complex formation directly by CD. Peptide selfassembly as a mechanism for membrane perturbation and fusion has also been described in the literature, when it involves a ␤-sheet structure (22,23,28). Oligomerization is in fact a recognized feature in the fusion mechanism of viral proteins, which may even involve the hydrophobic fusion peptides once they get exposed (3)(4)(5)27).…”

“…A similar multiple involvement in cell recognition (adhesion or penetration) and fusion has been proposed for other proteins, too, like fertilin (PH-30) (6,22,23), abalone sperm proteins (8,24,25), or viral proteins (3)(4)(5). In many instances, the fusogenic activity of such a protein has been attributed to a short fusion peptide or hydrophobic patch, which could then be characterized in detail with regard to its membrane interactions and secondary structure (22, 23, 26 -28).…”