[Amndz]

What is the general concept of two-state protein folding? All I know is that when denaturing a protein, if there is a broad transition between % folded protein and % unfolded protein then that means it is not two-state.. But I don't know what that exactly means.. Does it have anything to do with cooperative folding? Because I know that that is when part of the protein structure is disrupted, interactions between it and the remaining structure are disrupted and the structure is destabilized. I guess I just don't know what "two-state protein folding" is referring to..

Thanks in advance!

[Yggdrasil]

In a two-state model of protein folding, the protein can occupy only one of two states: the unfolded state or the folded state.  Here, folding is considered as an all-or-none process.  Part of the explanation for why folding often follows the two-state model is the cooperativity of protein folding.  If folding is highly cooperative, disrupting one interaction in the protein will destabilize all other interactions, so the protein can never be partly folded, only fully folded or fully unfolded.

Other models of protein folding include folding intermediates giving a third state (or more states) that a protein can occupy.  The existence of an intermediate state between the folded state and the unfolded state will broaden the transition folded and unfolded protein when looking at the unfolding of a protein.