Cell adhesion molecules (CAMs) are typically transmembrane (TM) glycoprotein receptors that help specific types of cells to undergo a selective process of cell-cell or cell-matrix interactions and act as a molecular link between the intra- and extra-cellular environment. The outside environment of the cells is linked to the extracellular domain of CAMs, the inside of the cell to the cytoplasmic (intracellular) domain and the cell membrane to the TM domains. The cytoplasmic domain controls various cellular processes including migration, through association with the cytoskeletal filaments, and transportation of cues, through the signaling molecules within the cell. The extracellular domain may act as membrane receptor and help in physical interaction between two cells. They may also play a role of soluble receptors when cleaved by proteases. The TM domains are hydrophobic in nature, and they are threaded to plasma membrane, and thereby they prevent the TM proteins from free-floating. Proteases may cleave the cytoplasmic domain of CAMs which can then enter the nucleus as transcription factors.
CAMs are important mediators of cell-cell and cell-matrix interactions through high affinity binding on either side of the interacting cells or ligands present in the extracellular matrix. In addition to adherence these direct interactions between cells or cell-matrix through CAMs play vital roles in various cellular processes including embryogenesis, hematopoesis, angiogenesis, cellular growth and differentiation, migration and invasion and cancer progression and metastasis. The signal transmission from cell to cell or from the extracellular matrix to cell also takes place through CAMs. CAMs can reverse the entire cellular processes by switching their binding affinity from low to high. The number of CAM families is growing and few of them include immunoglobin-like superfamily, cadherins, integrins, receptor protein tyrosine phosphatases, selectins, hyaluronate receptors and di-peptidyl peptidase IV. Expression and function of CAMs differ depending on the cell type. In the post-genome era, the existing in vivo and in vitro techniques used to identify and understand the functions of CAMs turn out to be inadequate. Therefore, it becomes necessary to identify CAMs in silico, and this calls for a consolidated record of available CAMs and their functions.
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