Troy Cellmer, Laboratory of Chemical Physics, National Institutes of Health, 9000 Rockville Pike, Building 5, Room 106, Bethesda, MD 20892, Harvey W. Blanch, Chemical Engineering, University of California at Berkeley, 275 Tan Hall, Berkeley, CA 94720, and John M. Prausnitz, Chemical Engineering, University of California Berkeley, 201 Gilman Hall, Berkeley, CA 94720-1462.
Protein aggregation has been associated with over twenty human diseases, including Alzheimer's and Parkinson's diseases. Recent studies have shown that proteins not associated with disease can form aggregates with morphologies and structural characteristics similar to disease-associated aggregates. Consequently, it has been hypothesized that general mechanisms for aggregation exist, and that studies on non-disease related proteins can offer new insight into such mechanisms. We have studied the aggregation of the small alpha/beta protein, protein L. Protein L is of specific interest because a molecular model developed to study its folding has since been exploited to study aggregation behavior. Thus our experimental results can guide and validate computational studies aimed at obtaining a molecular-level picture of the aggregation process. In the presence of trifluoroethanol, and under conditions of low pH and high temperature, protein L forms fibrillar aggregates similar to those associated with disease. Kinetic studies suggest that in the presence of TFE, protein L aggregates via a linear-elongation mechanism with nucleus size of either two or three monomers. Under low pH and high temperature, the kinetics are more complicated. There is a pronounced lag phase that varies significantly from experiment to experiment. Additionally, the reversibility of the aggregation process was investigated by removing the chosen denaturant. These studies show that moderate changes in the solution pH promote fibril disruption. The degree of this disruption is dependent upon the fibril age, with older fibrils being more difficult to disrupt.