Stability and Unfolding Mechanism of the N-terminal beta-Hairpin from [2Fe-2s] Ferredoxin I by Molecular Dynamics Simulations

摘要

The stability and unfolding mechanism of the N-terminal beta-hairpin of the [2Fe-2S] ferredoxin from the blue-green alga Aphanothece sacrum in pure methanol,40% (v/v) methanol-water,and pure water systems were investigated by 10 ns molecular dynamics simulations under periodic boundary conditions.The beta-hairpin was mostly in its native-like state in pure methanol,whereas it unfolds dramatically following the 'zip-up' mechanism when it was placed in pure water.Both interstrand and inside-turn hydrogen bonds account for the stability of the beta-hairpin in its native-like conformtion,whereas hydrophobic interactions among nonpolar side chains are responsible for maintaining its stable loop-like intermediate structures in 40% (v/v) methanol-water.Reducing solvent polarity seems to increase the stability of the beta-hairpin in its native-like structure.Methanol is likely to mimic the partially hydrophobic environment around the N-terminal beta-hairpin by the subsequent alpha-helix.