text: One characteristic of adhesion GPCRs is their extended extracellular region.  This region is modular in nature, often possessing a variety of structurally defined protein domains and a membrane proximal GAIN domain.  In the aptly named Very Large G protein-coupled Receptor 1 VLGR1 the extracellular region extends up to almost 6000 amino acids. Human adhesion GPCRs possess domains including EGF-like (), Cadherin (), thrombospondin (), Immunoglobulin (), Pentraxin (), Calx-beta () and Leucine-rich repeats ().  In non-vertebrate species multiple other structural motifs including Kringle, Somatomedin B (), SRCR () may be contained with the extracellular region.  Since many of these domains have been demonstrated to mediate protein-protein interactions within other proteins, they are believed to play the same role in adhesion GPCRs.  Indeed, many ligands have been discovered for adhesion GPCRs (see ligands section).  Many of the adhesion GPCR possess long stretches of amino acids with little homology to known protein domains suggesting the possibility of new structural domains being elucidated within their extracellular regions.