Structural basis for the emission of violet bioluminescence from a W92F obelin mutant

Mutation of the Trp92 that is known to lie within the active site of the ph otoprotein obelin from Obelia longissima, results in a shift of the biolumi nescence color from blue (lambda (max) = 485 nm) to violet. The corrected s pectrum shows a new band with lambda (max) = 410 nm now contributing equall y to the one at longer wavelength. The crystal structure of this W92F obeli n determined at 1.72 Angstrom resolution shows that there is no significant change in the dimensions of the active site between WT obelin (recombinant Ca2+-regulated photoprotein from Obelia longissima) and the mutant. It is proposed that the bioluminescence spectral shift results from removal of a hydrogen bond from the indole of W92 nearby a hydroxyl belonging to the 6-p henyl substituent of the substrate coelenterazine. Propagation of fbis chan ge through a conjugated bond system in the excited state of the product coe lenteramide affects the coupling of the N1-position and the hydrogen-bonded Y138. (C) 2001 Published by Elsevier Science B.V. on behalf of the Federat ion of European Biochemical Societies.