An international group of scientists found that when the tubulin protein is enzymatically modified, sperm begin to move in a straight line, which may be one of the causes of infertility.
Proteins can be modified by other proteins called enzymes. The fact that such modifications occur has been known for a long time, but the results of such a process in many cases remain unknown.
For example, scientists were previously unaware of the role of modifications in tubulin, a protein that forms microtubules. These are long threads that are used to create scaffolds in cages. Despite the fact that microtubules are almost the same in all cells of our body, they perform a wide variety of functions.
One of the most unique functions of microtubules is found in the sperm tail or flagellum. Sperm flagella are essential for male fertility and sexual reproduction. In order for the sperm to float in a straight line, the tubulin protein must be modified. One such modification, called glycylation, has not yet been well studied.
In a new study, scientists found that without this modification, sperm mostly float in a circle. To find out why the lack of glycylation leads to impaired sperm motility and male subfertility, the team used cryoelectron microscopy to visualize the molecular structure of the flagellum and its molecular movers.
Analysis of mutant sperm flagella showed that they were correctly constructed, but the mutation interfered with the coordinated activity of axonemal dyneins – the motors that drive the flagella. This explains why sperm swimming was impaired.
The results provide direct evidence that microtubules play an active role in the regulation of fundamental biological processes. In addition, this research points to a new mechanism underlying male infertility.