But some proteins have marginal structural stability and can rapidly interconvert between two or more folds.
[2] Protein structures in a given environment were thought to be defined completely by their amino acid sequence.
This hypothesis was, however, challenged by observations that proteins could fold in two alternative conformations, such as the prion proteins which exist in a physiologically active cellular form and an insoluble form.
[2] Extending the concept of a protein that exists in a soluble and an insoluble form, for the bacterial transcription factor RfaH two entirely different structures were observed to coexist in solution.
[5] RfaH is a two-domain protein, the C-terminal domain (CTD) of which can fold into alpha-helical and, alternatively, into beta-barrel form.