Transmembrane proteins integrins

Cellular adhesion is performed by a large set of transmembrane proteins integrins, cadherins, selectins and Ig superfamily members (Ig-N-Cam, ICAM. ..). 

Integrins constitute a large family of a (3 heterodimeric cell surface, transmembrane proteins that interact with a large number of extracellular matrix components through a metal ion-dependent interaction. The term integrin reflects their function in integrating cell adhesion and migration with the cystoskeleton. 

A family of transmembrane proteins referred to as integrins is capable of interactions with extracellular ligands as well as with the cytoskeleton. These have been implicated in cell-to-cell interactions through the extracel-... 

Several families of integral proteins in the plasma membrane provide specific points of attachment between cells, or between a cell and extracellular matrix proteins. Integrins are heterodimeric proteins (two unlike subunits, a and /3) anchored to the plasma membrane by a single hydrophobic transmembrane helix in each subunit (Fig. 11-22 see also Fig. 7-30). The large extracellular domains of the a and /3 subunits combine to form a specific binding site for extracellular proteins... 

Integrins are transmembrane proteins of the plasma membrane that act both to attach cells... 

Focal adhesion plaque is the region on the surface of a cell which anchors it to the extracellular matrix. The attachment is made by transmembrane proteins, such as the integrins. 

Integrins are members of a laige family of transmembrane proteins that act as receptors for cell-adhesion molecules. Integrins are heteromeric proteins. The type of integrin expressed on the surface of a cell determines what kind of adhesion molecules and hence which cells can be bound. 

In contrast, proteins vary markedly in their lateral mobility. Some proteins are nearly as mobile as lipids, whereas others are virtually immobile. For example, the photoreceptor protein rhodopsin (Section 32.3.1). a very mobile protein, has a diffusion coefficient of 0.4 pm s f The rapid movement of rhodopsin is essential for fast signaling. At the other extreme is fibronectin, a peripheral glycoprotein that interacts with the extracellular matrix. For fibronectin, D is less than 10-4 pm2 s f Fibronectin has a very low mobility because it is anchored to actin filaments on the inside of the plasma membrane through integrin, a transmembrane protein that links the extracellular matrix to the cytoskeleton. 

Type XVII collagen is composed of three identical procollagen polypeptides, each about 1,500 amino acids in length. It has a tadpole-like shape under physiological conditions (deduced from rotary shadowing electron microscopy of bovine cell lines or the pure protein). The protein is one of very few proteins whose N- and C-termini are inverted with respect to the membrane. In nearly all transmembrane proteins, for example integrins, the C-terminus is cytosolic and the N-terminus is extracellular. In type XVII collagen, the cytosolic N-terminal domain comprises about a third of the amino acid residues... 

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