Class B GPCRs are divided into two subfamilies: B1 secretin receptors and B2 adhesion receptors. Members of the secretin receptor subfamily have large extracellular domains and bind to vasoactive intestinal peptide (VIP), pituitary adenylate cyclase-activating peptide (PACAP), corticotropin-releasing factor (CRF), parathyroid hormone (PTH), growth hormone-releasing hormone (GHRH), calcitonin gene-related peptide (CGRP), glucagon, and glucagon-like peptide (GLP). The adhesion receptor subfamily has nine subclasses and possesses unique N-terminal motifs, such as epidermal growth factor, cadherin, and immunoglobulin domains.
