Samuel M, Zhu C X, Villanueva G B, Tse-Dinh Y C
Department of Biochemistry and Molecular Biology, New York Medical College, Valhalla 10595.
Arch Biochem Biophys. 1993 Jan;300(1):302-8. doi: 10.1006/abbi.1993.1042.
Escherichia coli DNA topoisomerase I contains three Zn(II) in each enzyme molecule required for relaxation of negatively supercoiled DNA. Apoenzymes were prepared from both the intact topoisomerase (M(r) 97,000) and the truncated active form top85 (M(r) 85,000) that lacks the carboxyl terminal domain but still contains the three Zn(II). Fluorescence and circular dichroism spectroscopy were used to compare the apoenzymes with topoisomerase and top85 reconstituted with Zn2+. The results indicated structural changes affecting the environment of the tryptophan residues and increasing the alpha-helical and beta-sheets content of the protein occurred upon zinc removal. These structural changes probably account for the loss of enzyme activity.
大肠杆菌DNA拓扑异构酶I的每个酶分子中含有三个锌离子（Zn(II)），这对于负超螺旋DNA的松弛是必需的。脱辅基酶是从完整的拓扑异构酶（分子量97,000）和截短的活性形式top85（分子量85,000）制备而来的，top85缺乏羧基末端结构域，但仍含有三个锌离子（Zn(II)）。利用荧光光谱和圆二色光谱将脱辅基酶与用锌离子（Zn2+）重构的拓扑异构酶和top85进行比较。结果表明，去除锌后发生了影响色氨酸残基环境并增加蛋白质α-螺旋和β-折叠含量的结构变化。这些结构变化可能是酶活性丧失的原因。
