Legume lectins-a paradigm in quaternary structure variations arising from similar tertiary structural fold

Abstract

Proteins belonging to the legume lectin family are characterized by similarity in their tertiary structures and differences in their modes of quatemary association which are brought about by minor variations in amino acid sequences. It is observed that differences in the modes of their association cause them to adopt different stabilities and folding patterns as studied by differential scanning calorimetry and isothemwal denaturation experiments. The proteins with the canonical and the handshake mode of association show a two-state denaturation profile but differ in their calorimetric to van't Hoff enthalpy ratio, thus indicating that these proteins unfold in slightly different ways. In this class of proteins we also see a homotetrameric protein like the peanut agglutinin, which neither shows a D₂ nor a four-fold symmetry This kind of unusual structure confers upon it an unusual folding pathway where the presence of a partially unfolded and active monomeric intermediate is observed. Thus we see that these proteins are good specimens to study the effects of minor alterations in their sequences on their oligomeric association.