Mucus is a viscous material with a wide range of vital functions at the interface between the body and the outside world. It coats the cells that line the lungs, intestine and genital tract, where it provides a barrier against harmful substances and acts as a lubricant. In the intestine, as on other body surfaces, mucus also serves as a gatekeeper, excluding pathogens and admitting beneficial microorganisms.
The main components of mucus are mucins, which are proteins decorated with distinctive patterns of sugar molecules. These not only provide a food source for bacteria, but can also act as anchors to hold them in place when they bind to molecules on the walls of bacterial cells, called adhesives.
By binding to the adhesives of pathogens, secreted mucins in fluids, such as saliva and tears, can prevent these microbes from clumping together. Mucins can also dissolve pathogen “biofilms”.
Biofilms are an aggregation of bacteria that have worked together to form thin layers on teeth and other tissue surfaces. In some cases, biofilms can have a negative impact on health.
Therefore, the patterns of the sugar molecules in the mucins play a vital role in determining how the body interacts with microorganisms. However, mucins are difficult to isolate and study, so our understanding of how they work has been limited.
Now a team of researchers, led by the Copenhagen Center for Glycomics, has developed a way to create human mucins that show particular patterns of sugar molecules. In this way, they can genetically program laboratory cultures of human embryonic kidney cells to produce mucins that bind to specific bacterial adhesins.
Mucins “with prescription”
Those researchers believe that doctors could one day prescribe mucins that promote the growth of beneficial species or inhibit disease-causing species.“An incredible number of diseases have a connection to the intestinal flora, but we still know very little about how we can control the intestinal flora in the treatment of diseases. This is where synthetic mucins could open up new treatment options, as a prebiotic material”, explains Yoshiki Narimatsu, one of the lead authors of the study.
The researchers also speculate that artificial mucins could be used instead of antibiotics to treat bacterial infections. For example, doctors could use synthetic versions of mucins in saliva and tears to kill bacteria that would otherwise form harmful biofilms.
Competition for the influenza virus
Mucins could even be used to compete with the common flu virus and prevent it from infecting the cells that line the nose, windpipe, and lungs. To infect cells in the respiratory tract, the virus attaches itself to sugar molecules, called sialic acid, on cell membranes.
But to release newly created virus particles and continue infection, the virus has to use an enzyme to break its binding to sialic acids. These acids not only bind to free virus particles, preventing them from becoming blocked in host cells in the nose, lungs, or both, but they also compete for the use of the enzyme that releases new virus particles.