Molten globule-like state of peanut lectin monomer retains its carbohydrate specificity

A central question in biological chemistry is the minimal structural requirement of a protein that would determine its specificity and activity, the underlying basis being the importance of the entire structural element of a protein with regards to its activity vis à vis the overall integrity and stability of the protein. Although there are many reports on the characterization of protein folding/unfolding intermediates, with considerable secondary structural elements but substantial loss of tertiary structure, none of them have been reported to show any activity toward their respective ligands. This may be a result of the conditions under which such intermediates have been isolated or due to the importance of specific structural elements for the activity. In this paper we report such an intermediate in the unfolding of peanut agglutinin that seems to retain, to a considerable degree, its carbohydrate binding specificity and activity. This result has significant implications on the molten globule state during the folding pathway(s) of proteins in general and the quaternary association in legume lectins in particular, where precise subunit topology is required for their biologic activities.