Amyloid β-Sheet Secondary Structure Identified in UV-Induced Cataracts of Porcine Lenses using 2D IR Spectroscopy

TitleAmyloid β-Sheet Secondary Structure Identified in UV-Induced Cataracts of Porcine Lenses using 2D IR Spectroscopy
Publication TypeJournal Article
Year of Publication2017
AuthorsZhang TO, Alperstein AM, Zanni M T.
Secondary TitleJournal of Molecular Biology
Date Published04/2017
PublisherJournal of Molecular Biology
Abstract

Cataracts are formed by the aggregation of crystallin proteins in the eye lens. Many in vitro studies have established that crystallin proteins precipitate into aggregates that contain amyloid fibers when denatured, but there is little evidence that ex vivo cataracts contain amyloid. In this study, we collect two dimensional infrared (2D IR) spectra on tissue slices of porcine eye lenses. As shown in control experiments on in vitro αB- and γD-crystallin, 2D IR spectroscopy can identify amyloidogenic β-sheet secondary structure because this structure has exceptionally strong coupling and a high degree of ordering that creates characteristic diagonal and cross peaks. In ex vivo experiments of acid treated tissues, characteristic 2D IR features are observed and fibers >50 nm in length are resolved by TEM, consistent with amyloid fibers. In UV-irradiated lens tissues, fibers are not observed with TEM, but amyloidogenic β-sheet secondary structure is identified from the 2D IR spectra. The characteristic 2D IR features of amyloid β-sheet secondary structure are created by as few as 4 or 5 strands, and so identify amyloid secondary structure even if the aggregates themselves are too small to be resolved with TEM. We discuss these findings in the context of the chaperone system of the lens, which we hypothesize sequesters small aggregates, thereby preventing long fibers from forming. This study expands the scope of heterodyned 2D IR spectroscopy to tissues. The results provide a link between in vitro and ex vivo studies, and support the hypothesis that cataracts is an amyloid disease.

URLhttp://www.sciencedirect.com/science/article/pii/S0022283617301900
DOI10.1016/j.jmb.2017.04.014