Blasie C A, Berg J M
Department of Chemistry, The Johns Hopkins University, Baltimore, Maryland 21218, USA.
Inorg Chem. 2000 Jan 24;39(2):348-51. doi: 10.1021/ic990913y.
A family of proteins that contain presumed zinc-binding domains with the consensus sequence Cys-X4-CysX4-His-X7-His-X5-Cys has recently been identified, but the metal binding and structural properties of these domains have not been investigated. This consensus is striking because of the presence of five conserved potential zinc-binding residues. A peptide corresponding to the third putative zinc-binding domain from the transcription factor NZF-1 (hereafter NZF-13) has been synthesized and characterized. The UV-visible absorption spectroscopic properties of the cobalt(H) complex of this peptide demonstrate that metal binding is tetrahedral, and the position of the visible absorption bands suggests coordination by three cysteinates and one histidine. To identify which of the two conserved histidine residues acts a metal-binding residue, two histidine to alanine variant peptides were also synthesized. Both variant peptides bound cobalt(II) in a tetrahedral fashion; replacement of the first of the two histidines has a somewhat larger effect on the detailed shape of the absorption spectral features than does replacement of the second histidine. These results suggest that the metal-coordinating residues (italicized) are Cys-X4-Cys-X4-His-X7-His-Xs-Cys. However, simultaneous substitution of both histidine residues with alanine generated a peptide with much more dramatically affected metal binding properties. These observations suggests that the relatively modest effects observed for the singly substituted peptides may be due to metal interactions involving the remaining histidine. Because of these phenomena, further studies will be required to establish more conclusively the roles of the two histidine residues in metal binding and the potential significance of the apparent alternative histidine coordination.
最近发现了一个蛋白质家族，其包含推测的锌结合结构域，共有序列为Cys-X4-Cys-X4-His-X7-His-X5-Cys，但这些结构域的金属结合和结构特性尚未得到研究。由于存在五个保守的潜在锌结合残基，这个共有序列很引人注目。已经合成并表征了与转录因子NZF-1的第三个假定锌结合结构域相对应的肽（以下简称NZF-13）。该肽的钴（II）配合物的紫外可见吸收光谱特性表明，金属结合是四面体的，可见吸收带的位置表明由三个半胱氨酸盐和一个组氨酸配位。为了确定两个保守的组氨酸残基中哪一个作为金属结合残基，还合成了两个组氨酸到丙氨酸的变体肽。两种变体肽都以四面体方式结合钴（II）；替换两个组氨酸中的第一个对吸收光谱特征的详细形状的影响比替换第二个组氨酸的影响更大。这些结果表明，金属配位残基（斜体）是Cys-X4-Cys-X4-His-X7-His-X5-Cys。然而，将两个组氨酸残基同时替换为丙氨酸产生了一种肽，其金属结合特性受到更显著的影响。这些观察结果表明，对于单取代肽观察到的相对适度的影响可能是由于涉及剩余组氨酸的金属相互作用。由于这些现象，需要进一步研究以更确凿地确定两个组氨酸残基在金属结合中的作用以及明显的替代组氨酸配位的潜在意义。
