G Protein-Coupled Taste Receptors

The sense of taste in vertebrates distinguishes the five basic taste qualities-salty, sour, sweet, umami, and bitter-and is devoted to detecting and evaluating the chemical composition of food. Taste receptor research has made enormous progress in recent years, revealing constantly intriguing features of the different receptor types, indicating how the versatility of G protein-coupled taste receptors has helped to ensure survival during evolution. Although a single sweet taste receptor accommodates numerous natural and artificial sweet substances by multiple interaction sites, the almost countless number of bitter compounds present in nature required the development of several bitter taste receptors. This chapter describes the structures and functions of G protein-coupled taste receptors that respond to sweet, umami, and bitter stimuli and that recognize the majority of tastants. Because the potential existence of additional taste qualities has been intensely discussed recently, a section on G protein-coupled receptors responsive to free fatty acids has been included.