Figure 2.

Regulation of the Phosphorylation State of Free Fatty Acid Receptor 4 (FFA4): Potential Physiological Roles. Both mouse (m) [48], as illustrated here (red circles in the cartoon of the seven transmembrane domain organisation of the receptor structure, and red font in the sequence of specific amino acids within the indicated region of its primary amino acid sequence) and human [47] FFA4 become rapidly phosphorylated on two groups of Ser/Thr residues within the intracellular C-terminal tail of the receptor upon addition of an agonist ligand. Alteration to generate the phosphorylation-defective form (ph-def) results in extended maintenance of elevated Ca²⁺ levels when either wild-type mouse FFA4 (wt; black) or ph-def mouse FFA4 (grey) are expressed in HEK293 cells and exposed to an agonist ligand (red arrow). Generation of transgenic mice in which wild-type FFA4 is replaced with either a C-terminally HA epitope-tagged form of FFA4 (left-hand side) or a similarly epitope-tagged form of ph-def FFA4 (right-hand side) is allowing analysis of receptor expression patterns (see Figure 4 in the main text) and specific roles of agonist-mediated phosphorylation of FFA4. Studies using these animals are still to be reported in the primary literature.