Carver J A, Cooper P G, Truscott R J
Australian Cataract Research Foundation, Department of Chemistry, University of Wollongong.
Eur J Biochem. 1993 Apr 1;213(1):313-20. doi: 10.1111/j.1432-1033.1993.tb17764.x.
1H-NMR spectroscopic studies of a 46-kDa homodimer, beta B2-crystallin, from bovine eye lens are presented. beta B2-crystallin has terminal extensions extending from globular N- and C-terminal domains that are well resolved in the NMR spectra, whereas, in the main, resonances from the bulk of the protein are not observed. Using two-dimensional NMR methods on beta B2-crystallin, its synthesised terminal extensions and a proteolysed sample of beta B2-crystallin with a portion of its C-terminus removed, it was possible to assign resonances to most of the amino acids in the terminal extensions. One-dimensional experiments at various pH values provided H-2 chemical shifts for the three terminal extension histidines from which their pKa values were measured. It is concluded that the terminal extensions appear to be of little ordered conformation, are accessible to solvent and flex freely from the main body of the protein. The results of the NMR spectroscopic studies of beta B2-crystallin are in excellent agreement with those for the X-ray crystal structure [Bax, B., Lapatto, R., Nalini, V., Driessen, H., Lindley, P. F., Mahadevan, D., Blundell, T. L. & Slingsby, C. (1990) Nature 347, 776-780]. No change in the spectrum of beta B2-crystallin was observed in the presence of calcium, suggesting that the termini are not involved in calcium binding.
本文介绍了对来自牛眼晶状体的46 kDa同型二聚体βB2-晶体蛋白的1H-NMR光谱研究。βB2-晶体蛋白具有从球状N端和C端结构域延伸出的末端延伸部分，这些在NMR光谱中得到了很好的分辨，而蛋白质主体的共振信号在很大程度上未被观察到。通过对βB2-晶体蛋白、其合成的末端延伸部分以及去除了部分C端的βB2-晶体蛋白蛋白水解样品使用二维NMR方法，能够将共振信号分配给末端延伸部分的大多数氨基酸。在不同pH值下进行的一维实验提供了三个末端延伸组氨酸的H-2化学位移，并据此测量了它们的pKa值。得出的结论是，末端延伸部分似乎几乎没有有序构象，可与溶剂接触，并能从蛋白质主体自由弯曲。βB2-晶体蛋白的NMR光谱研究结果与X射线晶体结构的研究结果[Bax, B., Lapatto, R., Nalini, V., Driessen, H., Lindley, P. F., Mahadevan, D., Blundell, T. L. & Slingsby, C. (1990) Nature 347, 776 - 780]非常吻合。在有钙存在的情况下，未观察到βB2-晶体蛋白光谱的变化，这表明末端不参与钙结合。
