The role of some amino acid residues in coelenterazine binding site of mnemiopsin compared to coelenterate photoproteins(Article Uncorrected Proof)

Mnemiopsin، a Ca2+-regulated photoprotein from ctenophore Mnemiopsis leidyi، as coelentrate photoproteins emits flash blue light upon reacting with coelenterazine. In contrast to coelenterate photoproteins، there is a little information about the structure of chromophore binding site and bioluminescence mechanism in ctenophore photoproteins. In this study، three important amino acid residues in coelenterazine binding cavity of mnemiopsin were substituted by corresponding residues in the well-known coelentrate photoproteins. W59K، N105W and L127W mutants were constructed and characterized for investigation of hydrogen bond network around the important rings of coelenterazine. All three mutants are completely inactivated. In addition، the results of structural studies including CD، intrinsic and extrinsic fluorescence together with theoretical studies showed that these mutants، especially for N105W and L127W، have found different structural features. These results suggest the presence of the residues in binding cavity and/or a mechanistic role for these residues. It seems that arrangement of amino acid residues in the binding cavity of coelenterate and ctenophore photoproteins are different، so that the replacement of these residues with their corresponding residues in other group (such as mutations in this study) perturbs the structural integrity needed for bioluminescence activity.