Hierarchy of Lens Proteins Requiring Protection Against Heat-Induced Precipitation by the α Crystallin Chaperone

Abstract

Gel filtration of the water-soluble extract from bovine lens yields a group of proteins, emerging between the peaks of βHand βLcrystallins, which show a considerably greater sensitivity to heat-induced aggregation/precipitation than the far more abundant β and γ crystallins. However, the small heat shock protein: α crystallin was effective in protecting these trace constituents of the lens from precipitating out of solution at 55 °C (measured under the standard conditions in a pH 7.5 buffer containing 50 mmsodium phosphate, 100 mmNaCl, 1 mmEDTA and 0.05% NaN3). Prominent components of the precipitate, formed in the absence of a recombinant αB crystallin chaperone could be resolved by one- and two-dimensional electrophoresis. Identification by amino acid sequencing revealed that the heat-sensitive group of lens proteins comprised glyceraldehyde-3-phosphate dehydrogenase (Mr∼39 kDa), enolase (∼48 kDa), leucine aminopeptidase (∼52 kDa) and aldehyde dehydrogenase (∼53 kDa). These findings indicate for the first time that the aggregation of such minor lens constituents could possibly contribute to initiating the process of opacification in the development of cataracts.