Site-Directed Mutations in the C-Terminal Extension of Human αB-Crystallin Affect Chaperone Function and Block Amyloid Fibril Formation

PLOS ONE, October 2007

17940610

Teresa M. Treweek, Heath Ecroyd, Danielle M. Williams, Sarah Meehan, John A. Carver, Mark J. Walker

Alzheimer's, Parkinson's and Creutzfeldt-Jakob disease are associated with inappropriate protein deposition and ordered amyloid fibril assembly. Molecular chaperones, including alphaB-crystallin, play a role in the prevention of protein deposition. A series of site-directed mutants of the human molecular chaperone, alphaB-crystallin, were constructed which focused on the flexible C-terminal extension of the protein. We investigated the structural role of this region as well as its role in the chaperone function of alphaB-crystallin under different types of protein aggregation, i.e. disordered amorphous aggregation and ordered amyloid fibril assembly. It was found that mutation of lysine and glutamic acid residues in the C-terminal extension of alphaB-crystallin resulted in proteins that had improved chaperone activity against amyloid fibril forming target proteins compared to the wild-type protein. Together, our results highlight the important role of the C-terminal region of alphaB-crystallin in regulating its secondary, tertiary and quaternary structure and conferring thermostability to the protein. The capacity to genetically modify alphaB-crystallin for improved ability to block amyloid fibril formation provides a platform for the future use of such engineered molecules in treatment of diseases caused by amyloid fibril formation.