Fig 1. Engineering of light-activated RET receptors.

(A) hRET and dRET consist of an extracellular ligand-binding domain (LBD), single-span transmembrane domain (TMD) and intracellular domain (KD: kinase domain, CTD: C-terminal tail domain). Activation by a GFL and GFRα was shown to result in the formation of a human ternary complex (binding model of Schlee et al. [40]). (B) In light-activated Opto-h/dRET, the LOV domain of the AUREOCHROME1 photoreceptor of V. frigida is incorporated at the receptor C-terminus. (C) MAPK/ERK pathway activation in response to blue light (I = 250 μW/cm², λ = 470 nm, 8h continuous) for HEK293 cells transfected with Opto-hRET, Opto-dRET or Opto-dRET^MEN2B. The MAPK/ERK reporter utilizes a pathway-specific Elk1 trans-activator to induce transcription of luciferase (LUC; see Materials and Methods for details). Light units (LU; mean ± SD) for dark treated cells and illuminated cells are given (n = 6 to 12, three independent experiments; t-test, *: p < .0001).