Werten P J, Lindner R A, Carver J A, de Jong W W
Department of Biochemistry, University of Nijmegen, P.O. Box 9101, 6500 HB, Nijmegen, Netherlands.
Biochim Biophys Acta. 1999 Jul 13;1432(2):286-92. doi: 10.1016/s0167-4838(99)00123-5.
The sequence extensions of the beta-crystallin subunits have been suggested to play an important role in the oligomerization of these eye lens proteins. This, in turn, may contribute to maintaining lens transparency and proper light refraction. In homo-dimers of the betaA3- and betaB2-crystallin subunits, these extensions have been shown by (1)H-NMR spectroscopy to be solvent-exposed and highly flexible. In this study, we show that betaA3- and betaB2-crystallins spontaneously form mixed betaA3/betaB2-crystallin complexes, which, from analytical ultracentrifugation experiments, are dimeric at low concentrations (<1 mg ml(-1)) and tetrameric at higher protein concentrations. (1)H-NMR spectroscopy reveals that in the betaA3/betaB2-crystallin tetramer, the N-terminal extensions of betaA3-crystallin remain water-exposed and flexible, whereas both N- and C-terminal extensions of betaB2-crystallin lose their flexibility. We conclude that both extensions of betaB2-crystallin are involved in protein-protein interactions in the betaA3/betaB2-crystallin hetero-tetramer. The extensions may stabilize and perhaps promote the formation of this mixed complex.
β-晶状体蛋白亚基的序列延伸被认为在这些晶状体蛋白的寡聚化过程中起重要作用。反过来，这可能有助于维持晶状体的透明度和适当的光折射。在βA3-和βB2-晶状体蛋白亚基的同型二聚体中，通过（1）H-NMR光谱显示这些延伸是暴露于溶剂且高度灵活的。在本研究中，我们表明βA3-和βB2-晶状体蛋白自发形成混合的βA3/βB2-晶状体蛋白复合物，从分析超速离心实验来看，其在低浓度（<1 mg ml（-1））下为二聚体，在较高蛋白质浓度下为四聚体。（1）H-NMR光谱显示，在βA3/βB2-晶状体蛋白四聚体中，βA3-晶状体蛋白的N端延伸仍然暴露于水且灵活，而βB2-晶状体蛋白的N端和C端延伸均失去其灵活性。我们得出结论，βB2-晶状体蛋白的两个延伸均参与βA3/βB2-晶状体蛋白异源四聚体中的蛋白质-蛋白质相互作用。这些延伸可能稳定并可能促进这种混合复合物的形成。
