Intercellular adhesion molecule-5 (ICAM-5), also known as telencephalin, is an integral membrane glycoprotein expressed in neurons of mammalian telencephalons. ICAM-5 is a member of the immunoglobulin superfamily and shares 38 - 55% amino acid homology with other ICAMs. Structurally, ICAM-5 contains nine Ig domains that included 15 N‑glycosylation sites, a single transmembrane region, and C-terminal cytoplasmic tail (1).
As with other members of the ICAM family, ICAM-5 has been shown to be involved in cellular adhesion. ICAM-5 binds to the leukocyte integrin LFA-1 (CD11a/CD18) via its first NH2-terminal Ig domain. The ability of ICAM-5 to bind LFA-1 suggests that ICAM-5 may play an important role in immune responses in the central nervous system (2). Additionally, ICAM-5 has been found to promote homophilic binding via binding of the first Ig domain to Ig domains 4 - 5. Homophilic adhesion activity of ICAM-5 is regulated by a monomer/tetramer transition. ICAM-5 expression temporally parallels the onset of dendritic elongation and synaptogenesis during the postnatal period suggesting that ICAM-5 may provide a brain segment-specific cue for synaptogenesis or dendrite-dendrite interaction (3).
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