The strategic hyper-reactivity toward GSSG which avoids aggregation in the nascent lysozymes: from Cys94 in egg to...

The thousand times enhanced reactivity of a single cysteine (Cys94) toward oxidized glutathione, recently discovered in the molten globular status of the hen egg lysozyme, is possibly finalized in vivo to prevent amorphous aggregation of this enzyme during its nascent phase, similar to what was observed in vitro. This study verifies if this property is preserved also in the human lysozyme, which is the result of a divergent evolution pathway. Mass spectrometry, kinetic and spectroscopic evidence demonstrate that hyper-reactivity as well as its anti-aggregation effect are also present in the human enzyme, but surprisingly exercised by Cys6, a residue very distant from the expected Cys95. Remarkable differences of the reduced molten globular structures may justify this unexpected shift of hyper-reactive cysteine. These results suggest that hyper-reactivity toward oxidized glutathione, also found in other six proteins, is preserved during the divergent evolution of lysozyme and that this property may have an important role during the oxidative folding of other disulfides containing proteins.