Adhesion receptor proteins

Adhesion of neutrophils to endothelial cells employs specific adhesive proteins (integrins) located on their surface and also specific receptor proteins in the endothelial cells. (See also the discussion of selectins in Chapter 47.)... 

Other adhesion receptors that are structurally and functionally related include the receptors for fibronectin, vitronectin, platelet glycoproteins 13b and Ilia and the VLA (very-late antigen) series. All molecules involved in adhesion recognise the RGD motif and require the divalent cations Ca2+ and Mg2+ for binding. All are dimers of glycosylated proteins with relative molecular masses 95-190 kDa. There is also some sequence homology between the /J-chain (CD18) and one chain of the fibronectin receptor. 

Figure. 4. Principle of the cell adhesion to artificial materials. In cell culture media or body fluids, the material is spontaneously adsorbed with cell adhesion-mediating extracellular matrix proteins (e g., vitronectin, fibronectin). The cells then adhere to specific amino acid sequences of these proteins by their adhesion receptors of integrin or non-integrin type [38-41].

Eukaryotic cells have six general types of signaling mechanisms gated ion channels receptor enzymes membrane proteins that act through G proteins nuclear proteins that bind steroids and act as transcription factors membrane proteins that attract and activate soluble protein kinases and adhesion receptors that carry information between the extracellular matrix and the cytoslceleton. 

Here are two of many known examples of specific cell-cell adhesion. The species-specific reaggregation of dissociated cells of marine sponges (Chapter 1) depends upon a 20-kDa proteoglycan of unique structure209-211 together with a cell surface receptor protein and calcium ions. The recognition of egg cell surfaces by sperm212-214 is species... 

The significance of exon shuffling to protein evolution, in particular in respect to the development of multicellularity, is signified by a short inventory of processes involving proteins created by modular assembly. Exon shuffling facilitates the construction of proteins involved in regulation of blood coagulation, fibrinolysis, and complement activation, plus most constituents of the extracellular matrix, cell adhesion proteins, and receptor proteins [10, 57]. 

In platelets, signaling is initiated primarily through members of the heterotrimeric G protein-coiqtled femily of leceptois (seven transmembrane domains) and through adhesion receptors, and the signaling involves activation of both Ser/Thr kinases and tyrosine kinases. Neither G protein-coiqtled receptors nor adhesion receptors have intrinsic tyrosine kinase activity. However, NRTKs (with SH2-, SH3-, and proline-rich domains) are activated and initiate tyrosine phosphorylation reactions that in turn lead to the recmitment of signaling molecules to certain locations in the cell. These tyrosine kinases may phosphorylate submembranous proteins including receptors for cytoplasmic domains or components of the submembranous cytoskeleton of adhesion receptor-cytoskeleton... 

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