Sun T X, Liang J J
Center for Ophthalmic Research, Brigham and Women's Hospital, and Department of Ophthalmology, Harvard Medical School, Boston, Massachusetts 02115, USA.
J Biol Chem. 1998 Jan 2;273(1):286-90. doi: 10.1074/jbc.273.1.286.
Lens alpha-crystallin subunits alphaA and alphaB are differentially expressed and have a 3-to-1 ratio in most mammalian lenses by intermolecular exchange. The biological significance of this composition and the mechanism of exchange are not clear. Preparations of human recombinant alphaA- and alphaB-crystallins provide a good system in which to study this phenomenon. Both recombinant alphaA- and alphaB-crystallins are folded and aggregated to the size of the native alpha-crystallin. During incubation together, they undergo an intermolecular exchange as shown by native isoelectric focusing. Circular dichroism measurements indicate that the protein with a 3-to-1 ratio of alphaA- and alphaB-crystallins has the same secondary structure but somewhat different tertiary structures after exchange: the near-UV CD increases after exchange. The resulting hybrid aggregate is more stable than the individual homogeneous aggregates: at 62 degrees C, alphaB-crystallin is more susceptible to aggregation and displays a greater light scattering than alphaA-crystallin. This heat-induced aggregation of alphaB-crystallin, however, was suppressed by intermolecular exchange with alphaA-crystallin. These phenomena are also observed by fast performance liquid chromatography gel filtration patterns. The protein structure of alphaB-crystallin is stabilized by intermolecular exchange with alphaA-crystallin.
晶状体α-晶状体蛋白亚基αA和αB的表达存在差异，在大多数哺乳动物晶状体中通过分子间交换形成3:1的比例。这种组成的生物学意义以及交换机制尚不清楚。人重组αA-和αB-晶状体蛋白的制备为研究这一现象提供了一个良好的系统。重组αA-和αB-晶状体蛋白均折叠并聚集至天然α-晶状体蛋白的大小。共同孵育时，如天然等电聚焦所示，它们会发生分子间交换。圆二色性测量表明，αA-和αB-晶状体蛋白比例为3:1的蛋白质在交换后具有相同的二级结构，但三级结构略有不同：交换后近紫外圆二色性增加。形成的杂合聚集体比单个均匀聚集体更稳定：在62℃时，αB-晶状体蛋白比αA-晶状体蛋白更容易聚集且表现出更大的光散射。然而，αB-晶状体蛋白的这种热诱导聚集通过与αA-晶状体蛋白的分子间交换得到抑制。快速高效液相色谱凝胶过滤图谱也观察到了这些现象。αB-晶状体蛋白的蛋白质结构通过与αA-晶状体蛋白的分子间交换得以稳定。
