A synchrotron X-ray scattering study on the structure of pepsin in solution

Solution small angle X-ray scattering (SAXS) is an effective technique for measuring structure and structural difference of protein under various environments, quantitatively. Structural characteristics of various conformational states of porcine pepsin were studied in terms of size and shape under several pH conditions by solution SAXS. Under nearly physiologically enzymatic active conditions, the reconstructed models exhibit a more extended C-terminal domain, when compare to the crystal structure. The structural differences between solution and crystal structure of pepsin can be accounted for the inherent conformations of the flexible subdomain in the C-terminal domain in solution under carefully controlled specific pH conditions. Furthermore, this flexibility may provide a clue that lead to the solution of enzymatic inactivity of pepsin under mild acidic conditions. The structural evidences presented may have important implication in establishing relationship between the structure of porcine pepsin and its enzymatic function.