Molten globule-like state of peanut lectin monomer retains its carbohydrate specificity - Implications in protein folding and legume lectin oligomerization

A central question in biological chemistry is the minimal structural requir ement of a protein that would determine its specificity and activity, the u nderlying basis being the importance of the entire structural element of a protein with regards to its activity vis a vis the overall integrity and st ability of the protein. Although there are many reports on the characteriza tion of protein folding/ unfolding intermediates, with considerable seconda ry structural elements but substantial loss of tertiary structure, none of them have been reported to show any activity toward their respective ligand s. This may be a result of the conditions under which such intermediates ha ve been isolated or due to the importance of specific structural elements f or the activity. In this paper we report such an intermediate in the unfold ing of peanut agglutinin that seems to retain, to a considerable degree, it s carbohydrate binding specificity and activity. This result has significan t implications on the molten globule state during the folding pathway(s) of proteins in general and the quaternary association in legume lectins in pa rticular, where precise subunit topology is required for their biologic act ivities.