Structure of the glycocalyx

Proteins in the sheath of cellular protrusions regulate the ability of cells to adhere to surfaces

To the point

• Protective layer around cilia: The layer known as glycocalyx consists of sugar-rich proteins (glycoproteins) and influences the mobility and signal transduction of cells.
• Main components: the glycoproteins FMG1 and FMG1A. FMG1A is a newly discovered variant of FMG1B.
• Other function: These proteins are not directly responsible for adhesion, but they regulate the adhesiveness of the cilia.

Biological cells often possess thin, hair-like protrusions on their surface known as cilia, which serve various functions ranging from movement to sensing environmental signals. Researchers from Germany and Italy have recently revealed new insights into the protective layer surrounding these cilia. This protective sheath, called the glycocalyx, consists of sugar-rich proteins (glycoproteins). As the first contact to the environment, it determines how cells adhere to surfaces, move and sense environmental signals. However, its exact structure was previously unknown.

The research team has now mapped the structure of this layer in the unicellular green alga Chlamydomonas reinhardtii in detail and identified the glycoproteins FMG1B and FMG1A as its main components. FMG1A is a previously unknown variant of FMG1B, and the two glycoproteins show a biochemical similarity to mucin proteins found in mammals. Mucins are also glycoproteins and a central component of protective mucus found in many organisms, for example on mucous membranes or in internal organs.

For their study, the team removed the two glycoproteins from the alga, which resulted in the cilia showing significantly increased stickiness. Nonetheless, the algal cells were still able to move on surfaces by means of the adhering cilia. This led the researchers to conclude that these proteins do not, as previously assumed, directly enable adhesion to surfaces and transmit the force needed for gliding motility from inside the cilium, but instead form a protective layer that regulates the adhesiveness of the cilia. ‘This discovery expands our knowledge of how cells regulate direct interaction with their environment,’ explains plant biotechnologist Michael Hippler from the University of Münster. ‘We are also gaining insights into how similar protective mechanisms might work in other organisms,’ adds Adrian Nievergelt from the Max Planck Institute of Molecular Plant Physiology in Potsdam who collaborated on the project with Dr Gaia Pigino’s research group at the Human Technopole in Milan.

The team used a wide range of cutting-edge imaging and protein analysis techniques, including cryogenic electron tomography and electron microscopy, fluorescence microscopy, mass spectrometry, as well as genetic manipulation to remove the glycoproteins from the algal genome.

The project was funded in part by the European Research Council (Horizon 2020), the German Research Foundation (DFG), the Human Frontier Science Program and the European Molecular Biology Organization.

 

Joint press release with the University of Münster.