By looking at research data spanning 14 years, researchers from the University of Virginia School of Medicine discovered the protein called sperm lysozyme-like protein 1 (SLLP1), which works like a tiny harpoon that allows the sperm to latch onto the egg and fertilize it.
The finding of the study, which was published in Andrology, provides scientists with a better knowledge on the structure of the sperm cell's acrosome, an organelle found in the head of the sperm and is known to host enzymes that aid the sperm in drilling through the gelatinous coating of the egg.
The findings from the collaboration of two labs at University of Virginia, also offer a new theory on the process of fertilization and may help in cancer research.
"One of the major proteins that is abundant in the acrosome found in the arterior region of the sperm head is crystallizing into filaments," said John Herr from the University of Virginia Department of Cell Biology. Herr also considers it as a new hypothesis emerging from the finding.
Herr's lab discovered the SLLP1 protein years ago but the lab had no means to determine its shape and structure. The SLLP1 from a family of proteins that is now recognized to be present in the acrosome. By collaborating with Wladek Minor' lab, also at the University of Virgina, it was shown that the protein form the spiky filaments at the sperms head.
Minor's team captured SLLP1 within a static crystal, which was then cooled to cryogenic temperature in order to prevent decay. The researchers then blasted the crystal with X-rays.
The researchers could get an idea of the protein's shape by looking at the refraction of the X-ray, which is similar to using sonar to map out a shipwreck, and eventually came up with one of the first descriptions of a protein in sperm.
Study author Heping Zheng said that the SLLP1 protein is really essential because it is the first crystal structure from a protein that resides within the acrosome of the sperm.
The researchers said that the new understanding of the structure will serve as map for reproductive biologists studying how fertilization occurs.
"This computational model revealed complementarity between the conserved SLLP1/SAS1B interacting surfaces supporting the experimentally observed SLLP1/SAS1B interaction involved in fertilization," the researchers wrote in their study.
