Minireview: Diversity and Complexity of Signaling through Peptidergic G Protein-Coupled Receptors

The transmission of signals by G protein-coupled receptors (GPCRs) that use peptides as ligands is critical for function of the gastrointestinal system. Molecular cloning has indicated that GPCRs constitute the most diverse transmembrane receptor family with many of these genes expressed in the gastrointestinal system. In addition to this molecular diversity, it has become clear that signaling through GPCRs is highly complex, with a wide variety of mechanisms that underlie different signaling responses and pathways through the same receptor. This minireview will summarize some of the emerging concepts of peptidergic GPCRs: signaling diversity including coupling to different G proteins, multiple endogenous ligands that can mediate different effects through binding to their cognate receptors, and homo- and hetero-oligomerization of receptors to enable cross talk or to produce novel signaling units.