Adhesion Molecules: Role & Explanation

Instructor: Hilary North

Hilary is a biomedical researcher with a PhD in neuroscience.

What are adhesion molecules? Learn how cells sense their environments, form connections with other cells, and move through the body. This lesson describes the main types of adhesion molecules and their roles.

Adhesion Molecules

You probably know that your body is made up of trillions of individual cells, and that those cells are grouped together into distinct organs. But how do those cells stick together? Furthermore, how do those groups of cells manage to stay fixed in their proper place within the body? This lesson will answer those questions with an introduction to a very special element in the human body: cellular adhesion molecules.

Cellular adhesion molecules (CAMs) are specialized class of molecule that serves as a binding agent between cells. More specifically, CAMs are proteins that are attached to the surface of a cell and serve to adhere that cell to either a neighboring cell or corresponding adhesion molecules in the surrounding environment. The adhesion molecules that surround cells are able to sense and adhere to the extracellular matrix (ECM), the external scaffolding-like environment outside of a cell.

Multiple Roles

It is clear from the word 'adhesion' in 'cellular adhesion molecules' that these proteins serve a glue of sorts between cells and their environments. But CAMs can do much more. After all, they do not simply blindly stick to anything nearby; instead, they relay information to the cell regarding what is in the cell's surroundings. This will often prompt the cell to change position! When a cell needs to move through its environment, CAMs help accomplish this feat, by binding to the environment that surrounds the individual cell in the direction the cell must migrate, thus pulling the cell in a desired direction. CAMs also allow access to the cell's interior when any other agent needs to enter. A virus, for example, will bind to a CAM, and the CAM will usher it inside the cell.

So imagine these molecules in a number of roles. Firstly, they are the glue that keeps cells together. Secondly, they provide movement to a cell by sticking to the surrounding environment and pulling the cell along behind it, kind of like spiderman using his web to grab on to his environment and following after. CAMs also act as bouncers or doormen, providing access to other bodies into the cell's interior.

A variety of diseases and disorders are associated with dysfunctional CAM binding or activation. For example, many cancer cells are able to spread because CAMs acted improperly. Other conditions thought to involve CAM dysfunction include asthma, diabetes, complications following injuries, and various immune disorders. A great deal of medical research currently focuses on this group of molecules in an effort to cure these medical problems.

CAMs' Structure

Most CAMs are connected to the cell at its surface and are comprised of three regions:

  • The extracellular domain is located outside of the cell. This domain contains binding sites, or docking stations, for CAMs of other cells or that it interacts with on the ECM.
  • The extracellular domain is connected to the transmembrane domain, which is the portion of the CAM that is lodged in the membrane of the cell.
  • The intracellular domain is usually attached to the cytoskeleton of the cell, which is the scaffold that gives each cell its shape. The intracellular domain will also often contain binding sites for various types of molecules inside the cell, such as messengers that can relay information about what the cell has contacted on the outside. In this way, CAMs function not just as physical adherents for cells but also as a means of communication between neighboring cells.

Types of Adhesion Molecules

There are five main classes of CAMs:

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