Influence of the intramolecular disulfide Cys46-Cys55 bridge on the interaction of human neuroglobin with SDS

Human neuroglobin (hNgb) is a globin involved in the protection of neurons and retinal cells which features an intramolecular disulfide bond between Cys46 and Cys55 under oxidative conditions. Here, conformational changes and oxidative degradation of hNgb wt and its C46AC55A mutant, lacking the disulfide bridge, were investigated in the presence of sodium dodecyl sulfate (SDS) by electronic absorption spectroscopy, intrinsic fluorescence emission and circular dichroism. Both proteins are found to undergo multiple SDS-induced conformational changes resulting in the formation of two non-native high spin species (HS1 and HS2). Moreover, increasing SDS concentration enhances the rate of heme breakdown by H₂O₂. Deletion of the Cys46-Cys55 disulfide bridge amplifies the conformational effect of SDS and appreciably increases heme oxidative degradation by H₂O₂.