The structures, called amyloid fibrils, are also implicated in neurodegenerative conditions such as Alzheimer's and Parkinson's, and in prion diseases like Creutzfeldt-Jacob and mad cow disease.
The results pinpoint a critical intermediate step in the chemical pathway that leads to amyloid fibril formation. With the new culprit in view, future work could target a possible treatment, such as designing an inhibitor to interfere with the harmful pathway.
An amyloid fibril is a large structure consisting of misfolded proteins. Such fibrils form plaques, or areas of tissue damage, that researchers can observe with microscopes. Fibrils are believed to arise when proteins deviate from their normal 3D structures and instead adopt misfolded states that tend to clump together.
Like puzzle pieces, proteins are only useful when they have the correct shape. And since the fibrils they form when misfolded are strong, scientists believe that hope primarily lies not in dismantling them, but in heading off the folding errors.
The researchers used two main approaches to identify the intermediate step and understand the pathway.
University of Wisconsin-Madison professor Martin Zanni used a sophisticated technique that relies on 2-D infrared spectroscopy to follow the sequence of events in the chemical reactions leading to fibril formation. His technique can measure extremely fast processes using very small samples.
Then Juan de Pablo and Chi-Cheng Chiu from the University of Chicago's Institute for Molecular Engineering interpreted Zanni's measurements with data from molecular simulations to arrive at a complete picture of the early events leading to amyloid formation.
De Pablo and Chiu used Intrepid, an IBM Blue Gene/P computer system at the Argonne Leadership Computing Facility (ALCF), and resources at the University of Chicago Research Computing Center. De Pablo and Chiu composed, ran and interpreted large-scale computer simulations of the pathway in action, and the results supplied an essential model of the molecular steps involved in the reaction.
Together, researchers located an entire step that had been missing, and whose absence had been fuelling confusion.
The new data show that both structures occur as the reaction changes over time. Transient rigid beta-sheets form, then morph into floppy protein loops, which finally take the form of more beta-sheets. The final beta-sheets bind together and stack up to form the damaging fibrils.
The focus now will be to target the new intermediate step. With more data, researchers could design an inhibitor drug to bind to the offending protein, block the molecule and halt the pathway's progression.
The study is published in the Proceedings of the National Academy of Sciences.