title: Membrane interactions of the putative fusion peptide (MF alpha P) from fertilin-alpha, the mouse sperm protein complex involved in fertilization.
abstract: Mammalian fertilization depends upon successful binding and fusion between the membranes of the spermatozoon and the oocyte. These processes are thought to be mediated by a series of protein-protein interactions in which sperm antigens known as fertilins are thought to play a key role. Using a recently developed fluorescence technique, the interactions of the oligopeptide sequence corresponding to the fusogenic domain of mouse fertilin-alpha (MF alpha P) and phospholipid vesicles have been investigated. Following stopped-flow mixing, MF alpha P bound rapidly to phospholipid membranes in a co-operative manner with a Hill coefficient of 2.4 and binding rate constants in excess of 1000 s-1. The co-operative nature of the binding process is suggested to represent evidence of a structural mechanism to prevent egg fertilization by immature spermatozoa. The subsequent membrane insertion was found to take place over a longer time period (with rate constants of up to 6.3 s-1), and was linear with respect to peptide concentration. Comparison of these processes with similar time-resolved circular dichroism measurements revealed that changes in peptide secondary structure were very rapid. Fourier transform infrared spectroscopy measurements confirmed changes in the secondary structure of MF alpha P during interaction with PC phospholipid membranes, indicating that the peptide is mainly present in a beta-structure with a small proportion of alpha-helix. These results are consistent with the hypothesis that fertilin-alpha is the fusogenic species with an important role in fertilization.
authors.affiliation: Institute of Food Research, Norwich Research Park, Colney, UK.
authors.forename: C A
authors.initials: CA
authors.lastname: Wolfe
authors.forename: J
authors.initials: J
authors.lastname: Cladera
authors.forename: S
authors.initials: S
authors.lastname: Ladha
authors.forename: S
authors.initials: S
authors.lastname: Senior
authors.forename: R
authors.initials: R
authors.lastname: Jones
authors.forename: P
authors.initials: P
authors.lastname: O'Shea
mesh_terms: D051722:ADAM Proteins; D000595:Amino Acid Sequence; D000818:Animals; D002942:Circular Dichroism; D000072196:Fertilins; D005306:Fertilization; D019793:Fluorescein / Q000378:metabolism; D008051:Lipid Bilayers / Q000378:metabolism; D008297:Male; D008562:Membrane Glycoproteins / Q000737:chemistry / Q000378:metabolism* / Q000502:physiology; D008666:Metalloendopeptidases / Q000737:chemistry / Q000378:metabolism* / Q000502:physiology; D051379:Mice; D008969:Molecular Sequence Data; D010455:Peptides / Q000737:chemistry / Q000378:metabolism; D010714:Phosphatidylethanolamines / Q000378:metabolism; D010743:Phospholipids / Q000378:metabolism; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D013094:Spermatozoa / Q000737:chemistry*; D013997:Time Factors
chemical_list: D008051:Lipid Bilayers; D008562:Membrane Glycoproteins; D010455:Peptides; D010714:Phosphatidylethanolamines; D010743:Phospholipids; D051722:ADAM Proteins; C000606455:Adam1a protein, mouse; D000072196:Fertilins; D008666:Metalloendopeptidases; D019793:Fluorescein