Oxidation of gamma II-crystallin solutions yields dimers with a high phase separation temperature.
Aqueous solutions of the bovine eye lens protein gamma II (or gamma B)-crystallin at neutral pH show a gradual increase in phase separation temperature, Tph, when allowed to stand for several weeks at room temperature without reducing agents. In a typical experiment, the Tph of the protein solution (218 mg/ml) increases from 2.5 +/- 1 degree C to 32.5 +/- 1 degree C after 21 days, and a new protein species, gamma IIH, is formed. The Tph of pure gamma IIH is at least 40 degrees C higher than that of pure gamma II. The average apparent hydrodynamic radius is 36 A for gamma IIH compared to 26 A for gamma II. The molecular mass of gamma IIH is approximately 41.5 kDa compared to 20 kDa for native gamma II. Therefore, gamma IIH is probably a dimer of gamma II crystallin. gamma IIH has a lower thiol content than gamma II and is not formed in the presence of dithiothreitol. We conclude that gamma IIH is a thiol oxidation product of gamma II-crystallin and is a dimer containing an intermolecular disulfide crosslink. Thus, some oxidative modifications of protein thiol groups lead to an increase in net attractive interactions between proteins. As a result, Tph increases and protein aggregates are formed. These two microscopic changes produce the increased light scattering associated with lens opacification.
Pande
J
J
Department of Physics, Massachusetts Institute of Technology, Cambridge 02139.
Lomakin
A
A
Fine
B
B
Ogun
O
O
Sokolinski
I
I
Benedek
G
G
D000818:Animals; D001704:Biopolymers; D002417:Cattle; D003459:Crystallins / Q000737:chemistry*; D004229:Dithiothreitol / Q000737:chemistry; D004591:Electrophoresis, Polyacrylamide Gel; D007908:Lens, Crystalline / Q000737:chemistry*; D010084:Oxidation-Reduction; D012996:Solutions; D013696:Temperature
D001704:Biopolymers; D003459:Crystallins; D012996:Solutions; D004229:Dithiothreitol