This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Acting as armor, a scaffold and a communication platform in one, our cells' plasma membrane lies at the heart of many crucial cellular processes. Traditionally, it has been thought to function through interactions among its various proteins and lipids.
Now, researchers have revealed a crucial yet often overlooked membrane component—complex sugar chains, known as glycans, carried by certain membrane lipids called gangliosides and many membrane proteins. Published in Nature Communications, a team from the Okinawa Institute of Science and Technology (OIST), Gifu University, the National Cancer Center Research Institute Japan, Kyoto University and collaborators shows that glycans on gangliosides in the same plasma membrane form weak, short-lived pairs. Repeated "fleeting encounters" of the glycans help couple the gangliosides, build membrane nanodomains and regulate epidermal growth factor receptor (EGFR) signaling, which in turn modulates cell division.
Professor Akihiro Kusumi, head of OIST's Membrane Cooperativity Unit and an author of the study, says, "Whether glycan-glycan interactions occur between molecules in the same plasma membrane has long challenged biologists. Using our advanced single-molecule imaging techniques, we were able to see these extremely weak, short-lived but frequent interactions directly in living cell membranes." The researchers chemically synthesized 39 fluorescent ganglioside analogs from all major ganglioside families distinguished by their glycan chains and introduced them into artificial and living cell membranes. Single molecules were tracked individually, revealing that gangliosides from all major families repeatedly formed short-lived "homodimers," in which two identical ganglioside molecules paired with each other via glycan-glycan interactions.
These homodimers lasted only about 0.1 to 0.2 seconds before falling apart, but new pairs were constantly forming. "Our cell membranes are bustling environments, with molecules constantly moving, meeting and separating," says Kusumi. "Sugar chains do not need to form stable complexes.
Instead, they meet only for a fraction of a second, but they do so again and again." Across a lifetime, our cells divide around 10 quadrillion times. Knowing when to divide, and when not to, is key to healthy tissue development. Excessive cell division is a distinctive feature of cancers.
Sitting within our cell membranes, epidermal growth factor receptor (EGFR) glycoproteins, which carry glycan chains, play central roles in regulating cell division and are often involved in cancer development. When EGFR molecules couple together to form dimers, signals are sparked within the cell that can initiate cell division. Usually, this coupling is triggered by binding of a molecule called EGF, but these dimers can also form incidentally, without EGF binding.
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