Fractionation of water-insoluble protein using sephacryl S-200 in formamide

NMR spin-echo studies of hydration properties of the molecular chaperone alpha-crystallin in the bovine lens

The water-binding properties of bovine lens alpha-crystallin, collagen from calf skin and bovine serum albumin (BSA), were investigated with various techniques. The water absorptive capacity was obtained in high vacuum desorption experiments volumetrically, and also gravimetrically in controlled atmosphere experiments. NMR spin-echo technique was used to study the hydration of protein samples and to determine the spin-spin relaxation times (T2) from the protons of water, absorbed on the proteins. Isolated bovine lenses were sectioned into 11-12 morphological layers (from anterior cortex through nucleus to posterior cortex). Crystallin profiles were obtained for each lens layer using thin-layer isoelectric focusing in polyacrylamide gel (IEF). The water content in relation to dry weight of proteins was measured in individual morphological lens layers. During the water vapor uptake P/P(0)=0.75, alpha-crystallin did not absorb water, suggesting that hydrophobic regions of the protein are exposed to the aqueous solvent. At P/P(0)=1.0, the absorption of water by alpha-crystallin was 17% with a single component decay character of spin-echo (T2=3 ms). Addition of water to alpha-crystallin to about 50% of its w/w in the protein sample showed T2=8 ms with only one single component decay of the spin-echo signal. The single component decay character of the spin-echo indicates at the tightly bound water by alpha-crystallin. Under a relative humidity P/P(0)=1.0, collagen and BSA absorbed correspondingly 19.3% and 28% of water and showed a two-component decay curve with T2 of about 5 and 40 ms. The findings demonstrate the presence of two water fractions in collagen and BSA which are separated in space. The IEF data suggest a tight binding of water with alpha-crystallin with similar distribution patterns in the lens layers. The IEF data demonstrate a possible chaperone-like function for alpha-crystallin in the nucleus and inner cortex of the lens, but not in the outer cortex. To conclude, it was found that alpha-crystallin can immobilize and bind water to a greater extent than other proteins such as collagen and BSA. These results shed new light on structural properties of alpha-crystallin and have important implications for understanding the mechanism of the chaperone-like action of this protein in the lens and non-ocular tissues.

Isotachophoresis and immunoelectrophoresis of water-soluble and -insoluble crystallins of the ageing bovine lens

Water-soluble (WS) and water-insoluble (WI) crystallins were prepared from calf and bovine lenses. The WS-crystallins were analyzed by capillary isotachophoresis and by immunoelectrophoresis with polyvalent and alpha-, beta-, gamma-crystallin specific antisera. The WI-crystallins were first solubilized in formamide and then analyzed by the same methods. The WS-crystallins, which increase in weight, but decrease in % with increasing age, show an increase of alpha-crystallins from 36 to 43%, an increase of beta-crystallins from 42 to 48% and a decrease of gamma-crystallins from 22 to 9%. In the WI-crystallins, which increase in weight and in % with increasing age, the alpha-crystallins form the main portion with an increase from 54 to 61%. The beta-crystallins in WI remain fairly constant at about 37% and the gamma-crystallins decrease from 8 to 2%. Quantitatively, the alpha-crystallin is the major constituent of the lens. The alpha-crystallin and the beta-crystallin components are increasingly incorporated in WI with increasing age. The gamma-crystallin components are selectively incorporated into WI-protein. Immunologically, alpha-, beta- and gamma-crystallins were detected by the polyvalent and specific antisera in WS- and in WI- crystallins.