Structure of a G protein-coupled receptor

The molecular structure of a G protein-coupled receptor includes seven membrane-spanning domains, a carboxy end (COOH), and an amino end (NH2). The amino end, which is glycosylated, resides on the outside of the cell and for most peptide hormones, participates in binding. The carboxy end is located inside the cell and contains many sites of phosphorylation (open circles). These regions are phosphorylated by regulatory proteins and often assist in receptor desensitization.