Alpha-crystallin, the major eye lens protein, is a molecular chaperone that plays a crucial role in the suppression of protein aggregation and thus in the long-term maintenance of lens transparency. Zinc is a micronutrient of the eye, but its molecular interaction with alpha-crystallin has not been studied in detail. In this paper, we present results of in vitro experiments that show bivalent zinc specifically interacts with alpha-crystallin with a dissociation constant in the submillimolar range (Kd approximately 0.2-0.4 mM). We compared the effect of Zn2+ with those of Ca2+, Cu2+, Mg2+, Cd2+, Pb2+, Ni2+, Fe2+, and Co2+ at 1 mM on the structure and chaperoning ability of alpha-crystallin. An insulin aggregation assay showed that among the bivalent metal ions, only 1 mM Zn2+ improved the chaperone function of alpha-crystallin by 30% compared to that in the absence of bivalent metal ions. Addition of 1 mM Zn2+ increased the yield of alpha-crystallin-assisted refolding of urea-treated LDH to its native state from 33 to 38%, but other bivalent ions had little effect. The surface hydrophobicity of alpha-crystallin was increased by 50% due to the binding of Zn2+. In the presence of 1 mM Zn2+, the stability of alpha-crystallin was enhanced by 36 kJ/mol, and it became more resistant to tryptic cleavage. The implications of enhanced stability and molecular chaperone activity of alpha-crystallin in the presence of Zn2+ are discussed in terms of its role in the long-term maintenance of lens transparency and cataract formation. Study holds ProTherm entries: 23100, 23101, 23102, 23103, 23104, 23105, 23106, 23107, 23108, 23109, 23110, 23111, 23112, 23113, 23114 Extra Details: Native to Intermediate alpha-Crystallin, Zn2+, Chaperone Function, Stability, bivalent metal ions.
Submitter: Connie Wang
Submission Date: April 24, 2018, 8:54 p.m.
|Number of data points||25|
|Proteins||Alpha-crystallin B chain|
|Assays/Quantities/Protocols||Experimental Assay: m ; Experimental Assay: dG_H2O|
|Libraries||Mutations for sequence MDIAIHHPWIRRPFFPFHSPSRLFDQFFGEHLLESDLFPTSTSLSPFYLRPPSFLRAPSWFDTGLSEMRLEKDRFSVNLDVKHFSPEELKVKVLGDVIEVHGKHEERQDEHGFISREFHRKYRIPADVDPLTITSSLSSDGVLTVNGPRKQVSGPERTIPITREEKPAVTAAPKK|