LAUSR

Understanding the factors governing stability of proteins is fundamentally and industrially important topic in protein science. Bacterial alpha amylases are industrially important enzymes which are involved in the breakage of α-1, 4-glycosidic bonds in starch. Current study is focussed on elucidating the role of non-covalent interactions in the differential stability of alpha amylases from thermophilic like Bacillus licheniformis (BLA) and mesophilic Bacillus amyloliquefaciens (BAA). The conformational stability of BLA is slightly higher than BAA in GdmCl which are 2.94 and 2.53 kcal/mol respectively. BLA does not unfold even in 8.0 M urea at pH 7.0, while for BAA, the conformational stability in urea is calculated to be 2.22 kcal/mol. A structure-function relationship study of BLA reveals the non-coincidental unfolding by far UV-CD, enzyme activity and tryptophan fluorescence which indicates the presence of partially unfolded intermediates. The existence of intermediates in BLA during GdmCl induced unfolding was further confirmed by ANS fluorescence. The unfolding kinetics of both enzymes showed biphasic nature with slower unfolding of BLA compare to BAA pointing towards the higher kinetic stability of BLA than BAA. Taken together, our work demonstrates that the higher stability of BLA is mainly due to the combination of ionic and hydrophobic interactions.