Fig. 1.

Schematic diagrams of GLuc complementation constructs and ligand– receptor interaction illustrated for CXCL12 and CXCR4. (a) Complementation reporter constructs with chemokine CXCL12 fused via a linker to CGLuc and NGLuc fused with an intervening linker to seven-transmembrane chemokine receptor CXCR4. These positions of NGLuc and CGLuc enzyme fragments allow complementation to occur in both extracellular and intracellular compartments. We also tested constructs with CXCL12 fused to NGLuc and CGLuc fused to CXCR4, but these reporters produced less bioluminescence upon ligand–receptor binding. (b) Binding of CXCL12-CGLuc to NGLuc-CXCR4 reconstitutes GLuc activity to oxidize the substrate coelenterazine and produce bioluminescence (fi gure adapted from ref. 10)