G protein-coupled receptors (GPRs) are a protein family of transmembrane receptors that transmit an extracellular signal (ligand binding) into an intracellular signal (G protein activation). GPR signaling is an evolutionarily ancient mechanism used by all eukaryotes to sense environmental stimuli and mediate cell-cell communication. GPRs all have seven membrane-spanning domains and extracellular loops that can be glycosylated. These extracellular loops also contain two highly conserved cysteine residues which create disulfide bonds to stabilize the receptor structure. SREB1 (super conserved receptor expressed in brain 1), also known as GPR27 (G protein-coupled receptor 27), belongs to the SREB subfamily of GPRs that are expressed in the central nervous system. SREB1 may function as an amine-like GPR.