Spectroscopic Investigation into Papain Conformational Changes in the Presence of an Anionic Surfactant

Abstract

Globular proteins contain substantial numbers of α- helices and β- sheets folded into a compact structure that is stabilized by both polar and non- polar interactions. The diversity of protein structures reflect the remarkable variety of functions performed by globular proteins: binding, catalysis, regulations etc. The hydrophobic part of amino acids side chains are buried, closely packed, in the interior of a globular protein while the hydrophilic amino acids of the side chains lie on the surface of the globular proteins and are usually exposed to the water. The most prominent form of protein aggregation is associated with a wide range of human disorders. The globular protein, Papain, is a proteolytic enzyme, obtained from the latex of Carica papaya. It is well studied due to it’s wide application in cosmetics, food industries and also has many medicinal applications. We have studied the aggregation of papain in the presence of sodium dodecyl sulfate (SDS) at pH 7.4 at room temperature with the help of different spectroscopic and microscopic techniques such as steady- state fluorescence using different extrinsic and intrinsic fluorophores, Circular Dichroism (CD), Field- Emission Scanning Electron Microscopy (FESEM) and Transmission Electron Microscopy (TEM). We have observed that aggregates were formed at higher concentrations of SDS and papain. The results have shown that β- sheets are formed at an expense of α- helices during aggreation at higher concentrations of SDS. Morphological studies reveals that the aggregates formed amorphous in nature, not fibrillar.