Structure based mechanism of the Ca(2+)-induced release of coelenterazine from the Renilla binding protein

The crystal structure of the Ca(2+)-loaded coelenterazine-binding protein from Renilla muelleri in its apo-state has been determined at resolution 1.8 A. Although calcium binding hardly affects the compact scaffold and overall fold of the structure before calcium addition, there are easily discerned shifts in the residues that were interacting with the coelenterazine and a repositioning of helices, to expose a cavity to the external solvent. Altogether these changes offer a straightforward explanation for how following the addition of Ca(2+), the coelenterazine could escape and become available for bioluminescence on Renilla luciferase. A docking computation supports the possibility of a luciferase-binding protein complex.