Immunoglobulin superfamily biochemistry

In the immunoglobulin superfamily, among the adhesion molecules involved in mutual recognition and interaction between cells, many molecules have a folding structure similar to the IgV region or C region, and their amino acid composition also has a certain degree of homology, which belongs to the immunoglobulin superfamily. Members of the family (immunoglobulin superfamily, IGSF). Refer to Chapter 3 for the structural characteristics and genetic structure of immunoglobulin superfamily molecules. The types, distribution and ligands of immunoglobulin superfamily adhesion molecules are shown in Table 2-2. The ligands of the immunoglobulin superfamily of adhesion molecules are mostly adhesion molecules of the immunoglobulin superfamily or molecules of the adhesin family.

For the structure and function of CD2, CD4, CD8, CD28 and CD58 molecules, please refer to Chapter 1 "Human Leukocyte Differentiation Antigen", MHC Class I Antigen and Class II Antigen see Chapter 6 "Major Histocompatibility Complex". This section will briefly introduce the structure of ICAM and VCAM-1 molecules.

1. ICAM-1 (intercellular adhesion molecule-1) ICAM-1 is one of the earliest discovered immune protein superfamily adhesion molecules, and later ICAM-2 and ICAM-3, their immunoglobulin domains The amino acid sequences have homology, and all can bind LFA-1 molecules. The distribution of different ICAM molecules in the body is quite different. ICAM-1 molecules are widely distributed, such as lymph node and tonsil vascular endothelial cells, thymic dendritic cells, tonsil and glomerular epithelial cells, leukocytes, macrophages and adult cells. Fibroblasts, IL-1, TNF-α, IFN and LPS can promote the expression of ICAM-1 molecules; ICAM-2 is more limited in distribution and mainly expresses vascular endothelial cells; while ICAM-3 is only expressed in blood cells. The ICAM-1 molecule is a single-chain transmembrane glycoprotein with a core polypeptide of 55 kDa. Due to the difference in the number of oligosaccharide molecules contained in ICAM-1 molecules on different types of cells, the molecular weight of ICAM-1 can be in the range of 80 to 11 kDa. The extracellular part of the ICAM-1 molecule has five immunoglobulin-like domains, and there is a connecting sequence between the second and third domains. It is rich in proline and is similar to the hinge region of immunoglobulin, which can be twisted. . With this junction as the boundary, the amino-terminal D1 and D2 domains can bind the LFA-1 molecule and rhinovirus, while the carboxy-terminal D3 domain can bind the Mac-1 molecule (Figure 2-3). ICAM-2 and ICAM-3 have 2 and 5 immunoglobulin domains in the extracellular membrane, respectively. The 2 domains of ICAM-2 molecule have 34% homology with the 2 domains at the N-terminus of ICAM-1, ICAM- The 1D1 domain has a key role in binding LFA-1 molecules.

Immunoglobulin superfamily Note: LFA: lymphocyte function-associated antigen

VCAM: vascular cell adhesion molecule

NCAM: nerve cell adhesion molecule

ICAM: intercellular adhesion molecule

PECAM: platelet endothelial cell adhesion molecule

Amino acid sequence, and also has the function of binding LFA-1 molecule.

The structure of other immunoglobulin superfamily adhesion molecules will be introduced in the relevant chapters of this book.

2. VCAM-1 (vascular cell adhesion molecule-1) vascular cell adhesion molecule, also known as induced cell adhesion molecule (vascular cell adhesion, INCAM), means activated by cytokines such as IL-1, TNF-α Expressed on vascular endothelial cells, the molecular weight is 100kDa or 110kDa, recently named CD106, and the ligand of VCAM-1 is the VLA-4 molecule distributed on the surface of leukocytes.

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