圆二色光谱研究Ni^(2+)诱导血清白蛋白构象变化

Conformational Transitions of Serum Albumin Based on Binding of Ni^(2+) Ion by Circular Dichroism Spectroscopy

在生理条件(pH7.43)下,采用时间扫描圆二色光谱(CD)研究了Ni2+诱导人血清白蛋白(HSA)或牛血清白蛋白(BSA)产生的构象变化。拟合计算远紫外CD光谱,结果表明,血清白蛋白在结合Ni2+过程中产生了鲜见的N→R态和R→T态两步构象变化。在结合的最初几分钟,血清白蛋白中的部分α-螺旋结构分别转变为了β-折叠、β-转角和无规卷曲,其含量从66%(N态)降低到约64%(R态)。随后发生了相反的变化,达到结合平衡时,α-螺旋结构含量上升到68.7%(T态)。近紫外CD光谱结果表明,血清白蛋白在结合Ni2+的过程中,二硫键及芳香氨基酸残基附近的微环境发生了缓慢扰动。CD光谱观察到该构象变化持续约3 h才达到平衡。对Ni2+诱导血清白蛋白产生两步构象变化的生理意义做了讨论,推测该构象变化能暴露结合位点,提供合适的立体配位空间,有助于血清白蛋白结合Ni2+。

The conformational transitions of human serum albumin （HSA） and bovine serum albumin （BSA） induced by binding of Ni^2＋ ions at physiological pH7. 43 were investigated with the time-scanning circular dichroism （CD） spectroscopy. The novel two-step conformational transitions of N→R state and R→T state are significantly revealed with the calculations of far-UV CD data for the first time. At the first minutes of binding,a part of α-helical structures turn into the remainder structures of β-sheet,and unordered,and the fraction of α-helix decreases from 66 % （N state） to about 64%-65% （R state）. The reverse transitions are observed in the following binding processes,in which the fractions of α-helix increase to 68. 7% （T state） at equilibrium. The continual perturbations of microenvironment around disulfide bridges and aromatic amino residues are detected with the near-UV CD spectra. The slow conformational transitions are observed for about 3 h induced by Ni^2＋ ion. The biological significance for the two-step conformational transition is also discussed here.