Inhibition of amyloid fibril formation of lysozyme by ascorbic acid and a probable mechanism of action

Amyloid fibrillation of proteins and polypeptides and their deposition in cells and tissues is associated with a number of pathological states collectively known as amyloid disorders. Inhibition of protein misfolding and aggregation is thus of utmost importance in the prevention and treatment of such diseases. There is a growing interest in identification of small molecules that can bind to native monomeric proteins or their partially unfolded states, thereby stabilizing them and preventing or delaying them from undergoing amyloid fibril formation. Here we report the inhibitory effect of ascorbic acid, an essential dietary component richly present in many natural food items, on the amyloid fibrillation of hen egg white lysozyme, a model protein for amyloid formation. The effect was dose dependent with more than 80% inhibition occurring even at only a five-fold molar excess of ascorbic acid. TEM images show complete absence of fibrils in the presence of ascorbic acid. From our spectroscopic and computational characterization of ascorbic acid binding to HEWL, we propose that ascorbic acid binds to the aggregation prone beta domain of HEWL, stabilizes the partially unfolded conformation and prevents further conformational changes leading to fibrillation. Hence ascorbic acid has a great therapeutic potential for amyloid disorders.