Structure–function studies of Murraya koenigii trypsin inhibitor revealed a stable core beta sheet structure surrounded by α-helices with a possible role for α-helix in inhibitory function

Abstract

Structure–function studies of Murraya koenigii trypsin inhibitor revealed a compact structure made of central β-sheet surrounded by α-helices with differences in structure and functional stability. Proteolysis studies, of native and heat-treated protein, demonstrated that inhibitor exhibited strong resistance to proteolysis by many proteases. However, the inhibitory activity gradually decreased with increasing temperature and was completely lost at 90 °C. CD studies, under native conditions, showed that inhibitor contains approximately 46% β-strand, 30.1% α-helical, 16.2% turn and 6.9% random coil structure. At increasing temperatures, however, helix to coil transition was observed. The ANS fluorescence study showed linear increase of fluorescence intensity without showing any melting transition. Correlating decrease in inhibitory activity and helical content at increasing temperatures suggest a possible role for α-helical structure in inhibitory function of the protein.