Chang G G, Lee H J, Chow R H
Department of Biochemistry, National Defense Medical Center, Taipei, Taiwan, Republic of China.
Exp Eye Res. 1997 Nov;65(5):653-9. doi: 10.1006/exer.1997.0372.
Animal lenses constitute many soluble proteins, which play a prominent role in eyes' light transparency. delta2-Crystallin, one of the major taxon-specific crystallins in duck lens, is a tetrameric protein consisting of four identical subunits, which contain endogenous argininosuccinate lyase activity. Under a neutral pH environment in this work, the protein was cross-linked with glutaraldehyde as tetrameric and dimeric forms with tetramer as the major form. Under acidic conditions, the protein was time-dependently dissociated into monomers with amino acid residues of pKa values 6.29+/-0.45 and 7.17+/-0.49 being involved in the monomer-monomer interactions and 6.20+/-0.10 and 8.88+/-0.07 in the dimer-dimer interactions. Duck lens delta2-crystallin thus possesses a double dimer structure (alpha2)2 with stronger monomer-monomer interactions than the dimer-dimer interactions. The acidic protein solution's reneutralization caused rapid reassociation of monomers into dimers and tetramers. The tetramer-dimer-monomer dissociation-reassociation thus is a pH-dependent freely interconvertible process.
动物晶状体包含许多可溶性蛋白质，这些蛋白质在眼睛的透光性方面发挥着重要作用。δ2-晶状体蛋白是鸭晶状体中主要的分类群特异性晶状体蛋白之一，是一种由四个相同亚基组成的四聚体蛋白，这些亚基具有内源性精氨酸琥珀酸裂解酶活性。在本研究的中性pH环境下，该蛋白与戊二醛交联形成四聚体和二聚体形式，其中四聚体为主要形式。在酸性条件下，该蛋白随时间解离为单体，参与单体-单体相互作用的氨基酸残基的pKa值为6.29±0.45和7.17±0.49，参与二聚体-二聚体相互作用的pKa值为6.20±0.10和8.88±0.07。鸭晶状体δ2-晶状体蛋白因此具有双二聚体结构(α2)2，其单体-单体相互作用比二聚体-二聚体相互作用更强。酸性蛋白质溶液的再中和导致单体迅速重新结合形成二聚体和四聚体。因此，四聚体-二聚体-单体的解离-再结合是一个依赖于pH的可自由相互转换的过程。
