Structure and Function of Somatostatin and its Receptors in Endocrinology.

Somatostatin analogs, such as octreotide (OCT), lanreotide, and pasireotide, which function as somatostatin receptor ligands (SRLs), are the main drugs used for the treatment of acromegaly. These ligands are also used as important molecules for radiation therapy and imaging of neuroendocrine tumors (NETs). Somatostatin receptors (SSTRs) are canonical G protein-coupled proteins (GPCRs) that play a role in metabolism, growth, and pathological conditions such as hormone disorders, neurological diseases, and cancers. Cryogenic electron microscopy (cryo-EM) combined with the protein structure prediction platform AlphaFold has been used to determine the three-dimensional structures of many proteins. Recently, several groups published a series of papers illustrating the three-dimensional structure of SSTR2, including that of the inactive/activated SSTR2-G protein complex bound to different ligands. The results revealed the residues that contribute to the ligand binding pocket and demonstrated that Trp8-Lys9 (the W-K motif) in somatostatin analogs is the key motif in stabilizing the bottom part of the binding pocket. In this review, we discuss the recent findings related to the structural analysis of SSTRs and SRLs, the relationships between the structural data and clinical findings, and the future development of novel structure-based therapies.