28.2:
Integrins
Integrins are a family of cell-adhesion receptors that bind ligands in the extracellular matrix or ECM to mediate cell-matrix adhesions.
They transition between an active and an inactive state. In the active form, they serve as mechanical linkers connecting the cytoskeleton to the extracellular matrix.
Integrin comprises noncovalently associated alpha and beta glycoprotein subunits, forming a transmembrane heterodimer.
The intracellular C-terminal tail of the beta subunit interacts with actin filaments in the cytosol through adaptor proteins such as talin and paxillin. Integrin’s large N-terminal extracellular domains bind to specific amino acid sequence motifs in ECM proteins, such as the RGD sequence in fibronectin.
The adhesion complex formed transmits signals bidirectionally across the plasma membrane with the help of effector proteins, thus facilitating cell motility, growth, and survival.
28.2:
Integrins
Animal and protozoan cells do not have cell walls to help maintain shape and provide structural stability. Instead, these eukaryotic cells secrete a sticky mass of carbohydrates and proteins into the spaces between adjacent cells. This network of proteins and molecules is called an extracellular matrix or ECM.
Some ECM proteins assemble into a basement membrane to which the remaining components adhere. Proteoglycans typically form the bulk of the ECM while fibrous proteins, like collagen, provide strength. Both proteoglycans and collagen are attached to fibronectin proteins, which, in turn, are attached to integral membrane proteins called integrins.
Mammalian integrins are heterodimeric transmembrane adhesion receptors comprising α and β glycoprotein subunits. Eighteen different α-chain genes and eight different β-chain genes dimerize in various combinations resulting in 24 types of integrins specific to vertebrates. They span the membrane and interact with proteins in the cytosol and the ECM. The α subunit contains a seven-bladed β-propeller head domain while the β subunit has an I-like head domain; together, they bind ligand. The ligand binding head is connected to two leg-like structures, one from each subunit. The β subunit interacts with the cytoskeletal protein and helps transmit signals in and out of the cell.
Adapted from section 5.1 Components and structure, 4.2 Epithelial tissue, and 3.4 Unique characteristics of eukaryotic cells, Openstax biology 2e
Suggested Reading
- David G. Menter, Raymond N. DuBois, "Prostaglandins in Cancer Cell Adhesion, Migration, and Invasion", International Journal of Cell Biology, vol. 2012, Article ID 723419, 21 pages, 2012. https://doi.org/10.1155/2012/723419
- Humphries, J. D., Byron, A., & Humphries, M. J. (2006). Integrin ligands at a glance. Journal of cell science, 119(19), 3901-3903.
- Humphries, M. J. (2000). Integrin structure. Biochemical Society Transactions, 28(4), 311-340.