Fig. 1.

Schematic demonstrating the principles underlying the injectable FGF21 drug depot. An ELP consisting of 120 repeats of the [Val-Pro-Gly-X_aa-Gly] pentapeptide, with a Val:Ala ratio of 4:1 at the X_aa position, is genetically fused to the N-terminus of FGF21. At temperatures below the tunable transition temperature (T_t) of the ELP, the fusion exists as miscible unimers, while above the T_t it forms an immiscible coacervate. Tuning the T_t below 37°C allows body heat to trigger the phase transition in vivo, forming a depot from which unimers dissolve over time.