Isoelectric focusing of crystallins in microsections of calf and adult bovine lens. Identification of water-insoluble crystallins complexing under nondenaturing conditions: demonstration of chaperone activity of alpha-crystallin

Abstract

Topographic studies of crystallin fractions from the young adult bovine lens revealed that lenses do not have a homogeneous distribution of crystallins. There are, however, gradual differences between the cortices and the nucleus. The isolated lenses were separated mechanically into lens equator and inner cylinder. The latter was then sectioned in a special sectioning machine into 11-12 morphological layers (from anterior cortex through nucleus to posterior cortex). Matters of the lens sections were separated into water-soluble (WS) and water-insoluble (WI) crystallins. The WI fractions were solubilized with 100% formamide, or dissolved into 7 M urea. Crystallin profiles were obtained for each lens layer, using thin-layer isoelectric focusing in polyacrylamide gel. WS crystallins from the lens equator revealed a separation into HM-, alpha L-, beta H-, beta L-, beta S- and gamma-crystallins. The WI fractions of the layers dissolved in urea gave a separation into the individual HM- (3 components), alpha L- (4 components), beta- (6 component groups), beta S- (2 components) and gamma- (11 components) crystallins in the different morphological layers. The results confirm that a significant age-related increase in several beta- and gamma-crystallins incorporated into alpha-crystallins exists in the patterns of WI fractions of the different layers from lenses of 2.2 and 5.9 years. The WI crystallins solubilized in formamide showed only the presence of HM weight and alpha-crystallin moieties, due to the action of chaperone activity of alpha-crystallin. The nature of the WI protein fraction in the separated lens layers reflected to the aggregated state of: alpha L-, beta L-, beta S- and gamma-crystallins in the different regions of the lens, concealed in the central cavity of the alpha-crystallin chaperone model.