DiMauro MA, Nandi SK, Raghavan CT, Kar RK, Wang B, Bhunia A, Nagaraj RH, Biswas A. Acetylation of Gly1 and Lys2 promotes aggregation of human γD-crystallin.
Biochemistry 2014;
53:7269-82. [PMID:
25393041 PMCID:
PMC4245984 DOI:
10.1021/bi501004y]
[Citation(s) in RCA: 24] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
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The human lens contains three major
protein families: α-,
β-, and γ-crystallin. Among the several variants of γ-crystallin
in the human lens, γD-crystallin is a major form. γD-Crystallin
is primarily present in the nuclear region of the lens and contains
a single lysine residue at the second position (K2). In this study,
we investigated the acetylation of K2 in γD-crystallin in aging
and cataractous human lenses. Our results indicated that K2 is acetylated
at an early age and that the amount of K2-acetylated γD-crystallin
increased with age. Mass spectrometric analysis revealed that in addition
to K2, glycine 1 (G1) was acetylated in γD-crystallin from human
lenses and in γD-crystallin acetylated in vitro. The chaperone ability of α-crystallin for acetylated γD-crystallin
was lower than that for the nonacetylated protein. The tertiary structure
and the microenvironment of the cysteine residues were significantly
altered by acetylation. The acetylated protein exhibited higher surface
hydrophobicity, was unstable against thermal and chemical denaturation,
and exhibited a higher propensity to aggregate at 80 °C in comparison
to the nonacetylated protein. Acetylation enhanced the GdnHCl-induced
unfolding and slowed the subsequent refolding of γD-crystallin.
Theoretical analysis indicated that the acetylation of K2 and G1 reduced
the structural stability of the protein and brought the distal cysteine
residues (C18 and C78) into close proximity. Collectively, these results
indicate that the acetylation of G1 and K2 residues in γD-crystallin
likely induced a molten globule-like structure, predisposing it to
aggregation, which may account for the high content of aggregated
proteins in the nucleus of aged and cataractous human lenses.
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