Diverse proteins containing a variable number of Ig-like domains chained in tandem.

A) immune system proteins: TCRs, MHCs, antibodies and many other cell surface receptors extracellular regions contain Ig-domains (CD8, CD4, CD22, CD28, PD1, CTLA4 etc.). B) Nervous system proteins: CEACAMs, contactins, that like sidekick or DSCAM proteins contain a 4-Ig horseshoe “superdomain” at the N-terminus (see section on Ig-Ig interfaces). MDGA proteins (MAM domain-containing glycosylphosphatidylinositol anchor) contain 7 Ig-domains followed by a MAM domain that has a jelly roll fold with similarities with the Ig-fold. C) Vascular system proteins: JAM proteins contain 2 Ig-domains in tandem, and VEGFR act as receptors for VEGF (Vascular endothelial growth factor) proteins. 3D models can be visualized in iCn3D links: Contactin1 https://structure.ncbi.nlm.nih.gov/icn3d/share.html?imRwYoJKmCpCaXYm7&t=Q12860; CEACAM1 https://structure.ncbi.nlm.nih.gov/icn3d/share.html?g89JayoAbbjN7Yg18&t=P13688; VCAM1 https://structure.ncbi.nlm.nih.gov/icn3d/share.html?9edsvYBJ43ZyPv9j8&t=P19320; VEGFR1 https://structure.ncbi.nlm.nih.gov/icn3d/share.html?SbL83DUuwccuJWtz8&t=Q8QHL3; JAM1 https://structure.ncbi.nlm.nih.gov/icn3d/share.html?6mGp5wdHxcxV4Cv98&t=1NBQ.