Could Sperm Harpoon Egg to Facilitate Fertilization?

Recently researchers of the University of Virginia School of Medicine have shown that spermatozoa harpoon the egg to facilitate fertilization. They have discovered a protein located on sperm head that forms harpoon-shaped spiky filaments, suggesting that these tiny filaments may help to bind the sperm and its target: oocyte.

Several years back, the same department discovered a protein, sperm lysozyme-like protein 1 (SLLP1), which has now been shown to form filaments. Protein of the same family has also been found to reside inside the acrosome also.

The team captured the protein within a static crystal following by cooling of the crystals to cryogenic temperatures to prevent decay. They then determined the shape of the protein by analysing the X-ray refraction. After numerous attempts they were able to produce one of the first descriptions of a sperm head specific protein.  This acrosomal protein has also been found to crystallize into filaments and involved in penetrating the outer layer of the egg. This finding leads to a new hypothesis about the very fine structure and molecular events during fertilization.

The team believe that this is an important protein, because it is not only the first mammalian sperm acrosomal protein whose crystal structure has been determined but also the first mammalian sperm protein with oocyte specific binding site to be structured and characterized. However structures of only nine mammalian sperm proteins are documented so far.

This new finding regarding the sperm acrosomal protein structure could act as a map for the reproductive biologists to explore the full event of fertilization.

Moreover knowing exactly which residue on sperm acrosome is interacting with which amino acid on the egg, can help to design drugs either to block or to assist the process of egg recognition and binding with oocyte. Thus this breakthrough could lead to the development of new fertility and contraceptive drugs through obstructing or helping those filaments in doing their job.

The finding represents a significant step forward to the fine dissection of the protein architecture of the sperm’s acrosomal matrix and suggests a new hypothesis concerning the events during fertilization.

The article is published in Andrology

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Arunima Maiti

Arunima Maiti

Biomedical scientist with special interest in reproductive biology.

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