RAMAN SPECTRAL STUDIES OF NUCLEIC-ACIDS .44. RAMAN-SPECTROSCOPY OF DNA-METAL COMPLEXES .1. INTERACTIONS AND CONFORMATIONAL EFFECTS OF THE DIVALENT-CATIONS - MG, CA, SR, BA, MN, CO, NI, CU, PD, AND CD
RAMAN SPECTRAL STUDIES OF NUCLEIC-ACIDS .44. RAMAN-SPECTROSCOPY OF DNA-METAL COMPLEXES .1. INTERACTIONS AND CONFORMATIONAL EFFECTS OF THE DIVALENT-CATIONS - MG, CA, SR, BA, MN, CO, NI, CU, PD, AND CD
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DOI：
10.1016/s0006-3495(93)81263-3
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发表时间：
1993-11-01
影响因子：
3.4
通讯作者：
THOMAS, GJ
中科院分区：
文献类型：
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作者：
DUGUID, J;BLOOMFIELD, VA;THOMAS, GJ
通过激光拉曼光谱研究了二价金属阳离子（Mg2+、Ca2+、Ba2+、Sr2+、Mn2+、Co2+、Ni2+、Cu2+、Pd2+ 和 Cd2+）与 DNA 的相互作用。小牛胸腺基因组 DNA（>23 KB 对）和单核小体片段（160 个碱基对）均被用作含有 5 重量% DNA 且金属：磷酸盐摩尔比为 0.6:1 的溶液中金属相互作用的靶标。拉曼差异光谱表明过渡金属阳离子（Mn2+、Co2+、Ni2+、Cu2+、Pd2+ 和 Cd2+）在 B-DNA 中引起最大的结构变化。拉曼（振动）带差异很大，表明 B 型主链部分无序、碱基堆积减少、碱基配对减少以及与嘌呤 (N7) 和嘧啶 (N3) 环上受体位点的特定金属相互作用。许多观察到的光谱变化与 B-DNA 热变性所伴随的光谱变化相似，表明金属与变性 DNA 的碱基相连。虽然 dT、dG 和 dC 的环外羰基可以稳定金属连接，但相关图显示羰基的扰动主要是金属诱导的双螺旋变性的结果。过渡金属与 DNA 磷酸盐的相互作用比与碱基的相互作用弱，但 Cu2+ 除外，它强烈干扰碱基和磷酸基团的振动。另一方面，B-DNA 的拉曼特征在很大程度上不受 Mg2+、Ca2+、Sr2+ 和 Ba2+ 的干扰，表明碱土金属与碱基和磷酸盐位点的相互作用要弱得多。一个值得注意的例外是碱土金属对 160 个碱基对 DNA 中嘌呤 N7 位点的适度扰动，其中 Ca2+ 造成的影响最大。相关图表明，分配给碱基环振动的拉曼带的扰动与分配给环外羰基和主链磷酸二酯基团的拉曼带的扰动之间存在很强的相互关系。然而，拉曼磷二氧基带（中心位于 1092 cm-1 附近）和其他拉曼带之间并不存在强相关性，这表明前者对二价金属阳离子引起的结构变化不高度敏感。对于 >23 千碱基对 DNA，二价阳离子引起的结构扰动比 160 碱基对 DNA 更大，拉曼差异光谱和形成不溶性聚集体的趋势都证明了这一点。在过渡金属存在的情况下，高分子量 DNA 的聚集在低至 11 摄氏度的温度下很明显。提出了 DNA 熔化和聚集之间的一种关系，其中主沟位点的初始金属结合局部破坏了 B-DNA 双螺旋的稳定性，导致碱基彼此远离并暴露出额外的金属结合位点。两个置换碱基的金属阳离子连接将允许单独的 DNA 链交联。据认为，聚集是由这些交联的扩展网络的形成引起的。
Interactions of divalent metal cations (Mg2+, Ca2+, Ba2+, Sr2+, Mn2+, Co2+, Ni2+, Cu2+, Pd2+ and Cd2+) with DNA have been investigated by laser Raman spectroscopy. Both genomic calf-thymus DNA (>23 kilobase pairs) and mono-nucleosomal fragments (160 base pairs) were employed as targets of metal interaction in solutions containing 5 weight-% DNA and metal:phosphate molar ratios of 0.6:1. Raman difference spectra reveal that transition metal cations (Mn2+, Co2+, Ni2+, Cu2+, Pd2+, and Cd2+) induce the greatest structural changes in B-DNA. The Raman (vibrational) band differences are extensive and indicate partial disordering of the B-form backbone, reduction in base stacking, reduction in base pairing, and specific metal interaction with acceptor sites on the purine (N7) and pyrimidine (N3) rings. Many of the observed spectral changes parallel those accompanying thermal denaturation of B-DNA and suggest that the metals link, the bases of denatured DNA. While exocyclic carbonyls of dT, dG, and dC may stabilize metal ligation, correlation plots show that perturbations of the carbonyls are mainly a consequence of metal-induced denaturation of the double helix. Transition metal interactions with the DNA phosphates are weak in comparison to interactions with the bases, except in the case of Cu2+, which strongly perturbs both base and phosphate group vibrations. On the other hand, the Raman signature of B-DNA is largely unperturbed by Mg2+, Ca2+, Sr2+, and Ba2+, suggesting much weaker interactions of the alkaline earth metals with both base and phosphate sites. A notable exception is a moderate perturbation by alkaline earths of purine N7 sites in 160-base pair DNA, with Ca2+ causing the greatest effect. Correlation plots demonstrate a strong interrelationship between perturbations of Raman bands assigned to ring vibrations of the bases and those of bands assigned to exocyclic carbonyls and backbone phosphodiester groups. However, strong correlations do not occur between the Raman phosphodioxy band (centered near 1092 cm-1) and other Raman bands, suggesting that the former is not highly sensitive to the structural changes induced by divalent metal cations.The structural perturbations induced by divalent cations are much greater for >23-kilobase pair DNA than for 160-base pair DNA, as evidenced by both the Raman difference spectra and the tendency toward the formation of insoluble aggregates. In the presence of transition metals, aggregation of high-molecular-weight DNA is evident at temperatures as low as 11-degrees-C. A relationship between DNA melting and aggregation is proposed in which initial metal binding at major groove sites locally destabilizes the B-DNA double helix, causing displacement of the bases away from one another and exposing additional metal binding sites. Metal cation linkage of two displaced bases would allow separate DNA strands to crosslink. Aggregation is proposed to result from the formation of an extended net work of these crosslinks.