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Neural cell adhesion molecule
Neural Cell Adhesion Molecule (NCAM, also the cluster of differentiation CD56) is a homophilic binding glycoprotein expressed on the surface of neurons, glia, skeletal muscle and natural killer cells. NCAM has been implicated as having a role in cell-cell adhesion, neurite outgrowth, synaptic plasticity, and learning and memory.
Additional recommended knowledge
Forms, domains and homophilic binding
There are at least 27 alternatively spliced NCAM mRNAs produced giving a wide diversity of NCAM isoforms . The three main isoforms of NCAM vary only in their cytoplasmic domain:
The extracellular domain of NCAM consists of five immunoglobulin-like (Ig) domains followed by two fibronectin type III (FNIII) domains. The different domains of NCAM have been shown to have different roles with the Ig domains being involved in homophilic binding to NCAM, and the FNIII domains being involved signalling leading to neurite outgrowth.
Homophilic binding occurs between NCAM molecules on opposing surfaces (trans-) and NCAM molecules on the same surface (cis-)1. There is much controversy as to how exactly NCAM homophilic binding is arranged both in trans- and cis-. Current models suggest trans- homophilic binding occurs between two NCAM molecules binding antiparallel between all five Ig domains or just IgI and IgII. cis- homophilic binding is thought to occur by interactions between both IgI and IgII, and IgI and IgIII, forming a higher order NCAM multimer. Both cis- and trans- NCAM homophilic binding have been shown to be important in NCAM “activation” leading to neurite outgrowth.
Another layer of complexity is created by the insertion of other "minor" exons in the NCAM transcript. The two most notable are:
NCAM can be posttranslationally modified by the addition of polysialic acid (PSA) to the fifth Ig domain which is thought to abrogate its homophilic binding properties and can lead to reduced cell adhesion important in cell migration and invasion. PSA has been shown to be critical in learning and memory. Removal of PSA from NCAM by the enzyme endoneuraminidase (EndoN) has been shown to abolish long term potentiation (LTP) and long term depression (LDP).
NCAM is thought to signal to induce neurite outgrowth via the Fibroblast growth factor receptor (FGFR) and act upon the p59Fyn signalling pathway.
In anatomic pathology, pathologists make use of CD56 immunohistochemistry to recognize certain tumors.
|This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Neural_cell_adhesion_molecule". A list of authors is available in Wikipedia.|