Radlick L W, Koretz J F
Center for Biophysics, Rensselaer Polytechnic Institute, Troy, NY 12180-3590.
Biochim Biophys Acta. 1992 Apr 8;1120(2):193-200. doi: 10.1016/0167-4838(92)90269-j.
The size of alpha-crystallin aggregates, as well as the structural organization of each particle's subunits, is currently unknown, although a number of different laboratories have suggested both structures and average molecular weights (Thomson, J.A. and Augusteyn, R.C. (1984) Proc. Int. Soc. Eye Res. 3, 152). One hypothesis, compatible with literature reports and consistent with what is known of subunit primary structure and physiological function, is that alpha-crystallin exists in vivo as a naturally occurring protein micelle (Sen, A.C. and Chakrabarti, B. (1991) Biophysical J. 59, 108a.) To test this hypothesis, experiments were performed on this protein to determine its behavior under increased hydrostatic pressure and the effect of its concentration on aqueous surface tension. With increasing hydrostatic pressure, the turbidity of an alpha-crystallin solution increases exponentially to a plateau at about 6000-8000 psi; upon release of pressure, the samples slowly return to their original turbidity level. Other naturally aggregating proteins, such as skeletal muscle myosin, demonstrate a decrease in turbidity under the same conditions. The surface tension of alpha-crystallin in aqueous solution decreases to a plateau with increasing protein subunit concentration, with an inflection point over the range 0.18-0.25 mM; cholate and other amphiphiles exhibit similar behavior. In contrast, plots of surface tension over the equivalent concentration range for other protein aggregates in the same buffer more closely approximate the types of curve obtained with short chain aliphatic acids. These results indicate that alpha-crystallin behaves like the protein version of a micelle.
目前尚不清楚α-晶状体蛋白聚集体的大小以及每个颗粒亚基的结构组织，尽管许多不同的实验室已经提出了结构和平均分子量（汤姆森，J.A.和奥古斯汀，R.C.（1984年）《国际眼科学会会议录》3，152）。一种与文献报道相符且与已知的亚基一级结构和生理功能一致的假设是，α-晶状体蛋白在体内以天然存在的蛋白质微团形式存在（森，A.C.和恰克拉巴蒂，B.（1991年）《生物物理杂志》59，108a）。为了验证这一假设，对这种蛋白质进行了实验，以确定其在静水压力增加时的行为以及其浓度对水表面张力的影响。随着静水压力的增加，α-晶状体蛋白溶液的浊度呈指数增加，在约6000 - 8000磅力/平方英寸时达到平稳状态；压力释放后，样品缓慢恢复到其原始浊度水平。其他天然聚集的蛋白质，如骨骼肌肌球蛋白，在相同条件下浊度会降低。随着蛋白质亚基浓度的增加，α-晶状体蛋白在水溶液中的表面张力降低至平稳状态，在0.18 - 0.25 mM范围内有一个拐点；胆酸盐和其他两亲物表现出类似的行为。相比之下，在相同缓冲液中其他蛋白质聚集体的等效浓度范围内的表面张力曲线更接近用短链脂肪酸获得的曲线类型。这些结果表明，α-晶状体蛋白的行为类似于蛋白质版本的微团。
