PROTEOGLYCANS CONTAIN A 4.6 ANGSTROM REPEAT IN MACULAR DYSTROPHY CORNEAS - X-RAY-DIFFRACTION EVIDENCE

Synchrotron x-ray diffraction patterns from macular corneal dystrophy (MCD) corneas contain an unusual reflection that arises because of an undefined ultrastructure with a periodic repeat in the region of 4.6 , in this study, we compared the wide-angle x-ray diffraction patterns obtained from four normal human corneas and four MCD corneas. Moreover , portions of two of the MCD corneas were pretreated with a specific g lycosidase to shed light on the origin of the 4.6 Angstrom reflection. None of the normal corneas produced an x-ray reflection in the region of 4.6 Angstrom, whereas all four of the MCD corneas did (MCD type I at 4.65 Angstrom and 4.63 Angstrom, MCD type II at 4.63 Angstrom and 4 .67 Angstrom). This reflection was diminished after incubation of the MCD tissues with either chondroitinase ABC or N-glycanase. The finding s indicate that glycosaminoglycans or proteoglycans contribute to the unusual MCD x-ray reflection and hence most likely contain a periodic 4.6 Angstrom ultrastructure. Furthermore, the results imply that perio dic 4.6 Angstrom MCD ultrastructures reside in either intact, unsulfat ed lumican molecules and regions of the CS/DS-containing molecules or in a region of a hybrid macromolecular aggregate formed by the interac tion of the two molecules.