'ZP domain' of human zona pellucida glycoprotein-1 binds to human spermatozoa and induces acrosomal exocytosis.
BACKGROUND
The human egg coat, zona pellucida (ZP), is composed of four glycoproteins designated as zona pellucida glycoprotein-1 (ZP1), -2 (ZP2), -3 (ZP3) and -4 (ZP4) respectively. The zona proteins possess the archetypal 'ZP domain', a signature domain comprised of approximately 260 amino acid (aa) residues. In the present manuscript, attempts have been made to delineate the functional significance of the 'ZP domain' module of human ZP1, corresponding to 273-551 aa fragment of human ZP1.


METHODS
Baculovirus-expressed, nickel-nitrilotriacetic acid affinity chromatography purified 'ZP domain' of human ZP1 was employed to assess its capability to bind and subsequently induce acrosomal exocytosis in capacitated human spermatozoa using tetramethyl rhodamine isothiocyanate conjugated Pisum sativum Agglutinin in absence or presence of various pharmacological inhibitors. Binding characteristics of ZP1 'ZP domain' were assessed employing fluorescein isothiocyanate (FITC) labelled recombinant protein.


RESULTS
SDS-PAGE and immunoblot characterization of the purified recombinant protein (both from cell lysate as well as culture supernatant) revealed a doublet ranging from ~35-40 kDa. FITC- labelled 'ZP domain' of ZP1 binds primarily to the acrosomal cap of the capacitated human spermatozoa. A dose dependent increase in acrosomal exocytosis was observed when capacitated sperm were incubated with recombinant 'ZP domain' of human ZP1. The acrosome reaction mediated by recombinant protein was independent of Gi protein-coupled receptor pathway, required extra cellular calcium and involved both T- and L-type voltage operated calcium channels.


CONCLUSIONS
Results described in the present study suggest that the 'ZP domain' module of human ZP1 has functional activity and may have a role during fertilization in humans.
Ganguly
Anasua
A
Reproductive Cell Biology Laboratory, National Institute of Immunology, Aruna Asaf Ali Marg, New Delhi-110067, India.
Bansal
Pankaj
P
Gupta
Tripti
T
Gupta
Satish K
SK
D000177:Acrosome / Q000378:metabolism / Q000502:physiology; D020101:Acrosome Reaction / Q000235:genetics / Q000502:physiology; D000818:Animals; D002478:Cells, Cultured; D004527:Egg Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D005089:Exocytosis / Q000502:physiology*; D005260:Female; D005306:Fertilization / Q000235:genetics / Q000502:physiology; D006801:Humans; D008297:Male; D008562:Membrane Glycoproteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D011485:Protein Binding / Q000235:genetics / Q000502:physiology; D017434:Protein Structure, Tertiary / Q000235:genetics / Q000502:physiology; D011956:Receptors, Cell Surface / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D013084:Sperm-Ovum Interactions / Q000235:genetics / Q000502:physiology*; D013094:Spermatozoa / Q000378:metabolism* / Q000502:physiology; D018411:Spodoptera; D000072216:Zona Pellucida Glycoproteins
D004527:Egg Proteins; D008562:Membrane Glycoproteins; D011956:Receptors, Cell Surface; D011994:Recombinant Proteins; C000606514:ZP1 protein, human; C000606515:ZP2 protein, human; C000606517:ZP3 protein, human; D000072216:Zona Pellucida Glycoproteins