Early events in thermal unfolding of apocytochrome b562 and its double-cysteine mutant as revealed by molecular dynamics simulation

Apocytochrome b562 (apocyt b562) with heme group removal and its double-cysteine mutant, dc-apocyt b562 (Arg98Cys/Tyr101Cys) containing a CXXCH heme-binding motif of cytochrome c, have been subjected to molecular dynamics (MD) simulation at high temperature (500 K). The early events upon thermal unfolding were found to be different between these two apoproteins as obtained from mutation studies. At the same time, the contribution of non-native interactions, such as hydrogen bonds and salt bridges, to protein stabilities were also analyzed in detail. The information provided by MD simulations is valuable for understanding the in vivo formation of b-type as well as c-type heme proteins.