Fig. 9.

Retinol-EGFP FRET demonstrating STRA6-catalyzed retinol exchange between RBP molecules. a Schematic diagram of the proposed mechanism of STRA6-catalyzed retinol exchange between RBP molecules. To demonstrate STRA6-catalyzed exchange between RBP molecules, apo-RBP is tagged with EGFP. Retinol binding to EGFP-RBP would lead to fluorescence resonance energy transfer between retinol and EGFP. b STRA6 catalyzes the transfer of retinol from untagged holo-RBP to EGFP-apo-RBP in a time-dependent manner (dark green), as shown by the increase in retinol-EGFP FRET. This transfer reaction does not happen in the absence of STRA6 (black) and is suppressed by LRAT (light green). Statistical significance (n = 3) was determined by Tukey's multiple comparison test (**p < 0.01)