A schematic diagram of GPR126 protein structure consisting of an N-terminal fragment (NTF) and a C-terminal fragment (CTF). The NTF encompasses most of the protein's large extracellular regions (ECRs) and is composed of newly identified five domains: a CUB (complement C1r/C1s, Uegf, Bmp1) domain, a PTX (Pentraxin) domain, a SEA (Sperm protein, Enterokinase, and Agrin) domain, a hormone binding (HormR) domain, and a conserved GPCR autoproteolysis-inducing (GAIN) domain. The CTF is C-terminal to the GAIN domain's GPCR proteolysis site (GPS), and composed of the 7TM domain and an intracellular C-terminal tail. N- and O-linked glycosylation are indicated as blue hexagons.