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Materials

Domain Structure Of Cataract Amyloids

Two-dimensional IR spectroscopy reveals surprise for crystallin amyloid fibrils

by Celia Henry Arnaud
February 13, 2012 | APPEARED IN VOLUME 90, ISSUE 7

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Credit: Proc. Natl. Acad. Sci. USA
Structural model of three γD-crystallin monomers in an amyloid fibril. The N-terminal domain is disordered, whereas the C-terminal domain forms a mixture of β-strands and loops.
09007-scicon-crystallinfibercxd.jpg
Credit: Proc. Natl. Acad. Sci. USA
Structural model of three γD-crystallin monomers in an amyloid fibril. The N-terminal domain is disordered, whereas the C-terminal domain forms a mixture of β-strands and loops.

Two-dimensional infrared spectroscopy reveals an unexpected structure for amyloid fibers formed from human γD-crystallin, which is a major component of cataracts (Proc. Natl. Acad. Sci. USA, DOI: 10.1073/pnas.1117704109). Martin T. Zanni of the University of Wisconsin, Madison; Sean M. Decatur of Oberlin College; and coworkers found this structure through a method that extends isotope-edited 2-D IR spectroscopy to entire proteins. In the past, isotopic labeling on the amide carbonyl was performed on one amino acid at a time, and the method was limited to peptides that could be made by solid-phase synthesis. Now, the team uses 13C to label the amides in an entire segment of a protein and leave other segments unlabeled. They stitch the segments together to form the complete protein by using an existing method called expressed protein ligation. They used the 2-D IR method for structural studies of human γD-crystallin. Earlier work suggested that the β-sheets associated with amyloid fibrils formed in γD-crystallin’s N-terminal domain. This study of the complete protein instead suggests that fibril nucleation and growth occur in the C-terminal domain.

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