Hierarchy of lens proteins requiring protection against heat-induced precipitation by the α crystallin chaperone

Purpose. To identify lens constituents which, though present only in low concentration, are more prone to heat-induced precipitation than the and 7 crystallins and require protection by the a crystallin chaperone. Methods. Greatest heat sensitivity (measured in 50 mM sodium phosphate, 0. l M NaCl, 1 iriM EDTA, 0.05% NaN3, pH 7.5) was seen in the fractions eluted between the /3H and L crystallins by gel filtration (Sepharose CL-6B; Inv. Ophthalmol. Vis. Sei. 36, S884, Abs. 4053, 1995). Proteins in the 1 hr, 55°C precipitate were resolved first by one and then by two-dimensional electrophoresis, transblotted and sequenced, either directly or after partial proteolysis. Results. Amino acid sequencing revealed that glyceraldehyde-3-phosphate dehydrogenase, a-enolase/r crystallin, aldehyde dehydrogenase and leucine aminopeptidase are among the most heat-sensitive of the lens constituents. Nevertheless, their precipitation at 55°C could be prevented by admixture of a crystallin. Conclusions. Enzymes, present in only trace quantities, could be a primary source of opacification in the lens without the protection afforded by the a crystallin chaperone. Supported by NIH grant EY03942.