Spectral tuning of obelin bioluminescence by mutations of Trp92

Abstract

The Ca2+-regulated photoprotein obelin was substituted at Trp92 by His, Lys, Glu, and Arg. All mutants fold into stable conformations and produce bimodal bioluminescence spectra with enhanced contribution from a violet emission. The W92R mutant has an almost monomodal bioluminescence (λmax=390 nm) and monomodal fluorescence (λmax=425 nm) of the product. Results are interpreted by an excited state proton transfer mechanism involving the substituent side group and His22 in the binding cavity.