Photoinactivation related dynamics of ctenophore photoproteins: Insights from molecular dynamics simulation under electric-field.

Photoinactivation is a common phenomenon in bioluminescence ctenophore photoproteins (e.g mnemiopsin, berovin and BfosPP) with still unknown mechanism. The activity of coelenterate photoproteins (e.g aequorin), which has high structural similarity with ctenophore photoproteins, is not affected by light. Recently, we have characterized the effects of light on ctenophore photoprotein mnemiopsin, in different conformations, which has demonstrated light induced structural changes, uniquely secondary structures, of both apo and holo mnemiopsin. This paper is further expansion of our previous work, by applying molecular dynamics simulations to investigate photoinactivation related dynamics of berovin at atomistic level, in comparison with aequorin, under the influence of electric component of electromagnetic field. The results have indicated that the intense electric filed could influence structure of both berovin and aequorin but in different manner, whereas moderate electric field only effects on berovin's structure remarkably. In this case, increased helicity of residues E180-M193 and decreased helical contents of L38-D46 and L125-D138 segments are considerable in berovin as well as flexibility elevation of calcium binding loops. These changes cause structural expansion of berovin, especially at N-terminal domain, in direction of electric field. In conclusion, the induced structural changes of mentioned helical parts together with elevated fluctuation of their adjacent segments, N26-D46 and M193-Y206, indicate the influence of light on substrate stabilizing residues, Arg41 and Y204. This condition could presumably leads to inactivation of bioluminescence reaction due to separation of substrate from the cavity of the protein.