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Your body is composed of trillions of cells, all working together to keep you alive. As you might imagine, this requires a massive infrastructure to hold everything together. This infrastructure is built at many levels. Huge structures, like bones and tendons, are built to support and move the entire body. Many of the spaces between cells are supported by connective tissue, which is built from a collection of sturdy molecular cables and sheets. Finally, an intimate, molecule-sized infrastructure is used to adhere cells directly to their neighbors.
Cadherins are one of the many molecules that glue cells together. They are long proteins that extend from the surface of the cell. The outer portion is composed of a series of folded domains arranged one after the next, and calcium ions bind between each domain, rigidifying the whole structure. If calcium is removed, however, the chain becomes floppy and is easily destroyed by protein-cutting enzymes. The tip of the chain has a special tyrosine amino acid, colored red here, that binds to cadherins on neighboring cells, adhering the two cells together.
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Biocurious is written by Andre Brown and Philip Johnson, since 2005. Content of the weblog is licensed under a Creative Commons Attribution-Share Alike 3.0 License.
There’s a paper in the latest issue of Science on cadherins and their role in the transition to multicellular animals (abstract below). According to King’s publications page there is free access to the article through this link.
The Premetazoan Ancestry of Cadherins
Monika Abedin and Nicole King
Cadherin-mediated cell adhesion and signaling is essential for metazoan development and yet is absent from all other multicellular organisms. We found cadherin genes at numbers similar to those observed in complex metazoans in one of the closest single-celled relatives of metazoans, the choanoflagellate Monosiga brevicollis. Because the evolution of metazoans from a single-celled ancestor required novel cell adhesion and signaling mechanisms, the discovery of diverse cadherins in choanoflagellates suggests that cadherins may have contributed to metazoan origins.