integrins
Summary
Integrins are transmembrane receptors, each made of an α and a β subunit, that bind extracellular matrix proteins such as fibronectin, collagen and laminin and connect to the cytoskeleton inside. Testable point: integrins link cell to matrix, while cadherins link cell to cell.
Detail
Meaning: Integrins are heterodimeric transmembrane proteins. Outside the cell they bind extracellular matrix (ECM) proteins such as fibronectin, laminin and collagen. Inside, adaptor proteins connect them to the cytoskeleton: usually actin at focal adhesions, or intermediate filaments at hemidesmosomes. They therefore anchor the cell and pass signals in both directions. Matrix contact can change intracellular signaling that affects migration, survival and growth, and intracellular signals can change how tightly an integrin grips the matrix.
On the MCAT: Passages on cell junctions or the ECM ask you to match each protein to its connection. Integrins join cell to matrix. Cadherins join cell to cell and depend on Ca²⁺. Connexins form gap junctions, and claudins and occludins form tight junctions. A typical experiment blocks integrins with an antibody or knocks out an integrin gene, then asks you to predict the result. Cells fail to adhere to a fibronectin-coated dish, or they migrate poorly. Questions may also ask which cytoskeletal element a junction connects to.
Common confusion: Students mix up integrins and cadherins because both are adhesion proteins. The binding partner settles it. Integrins bind ECM components, while cadherins bind cadherins on a neighboring cell. Integrins are also not just glue. They act as signaling receptors that relay information about the matrix into the cell.
Sources
- Molecular Biology of the Cell
- Lehninger Principles of Biochemistry
- Campbell Biology
Written for the MCAT and checked before it was published. For study reference only. Spotted an error? Let us know.