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人乳头瘤病毒E2转录调节因子二聚体β桶状DNA结合结构域“单链”变体的稳定性增加及DNA位点识别能力增强

Increased stability and DNA site discrimination of "single chain" variants of the dimeric beta-barrel DNA binding domain of the human papillomavirus E2 transcriptional regulator.

作者信息

Dellarole Mariano, Sánchez Ignacio E, Freire Eleonora, de Prat-Gay Gonzalo

机构信息

Instituto Leloir and IIBBA-Conicet, Patricias Argentinas 435 (1405), Buenos Aires, Argentina.

出版信息

Biochemistry. 2007 Oct 30;46(43):12441-50. doi: 10.1021/bi701104q. Epub 2007 Oct 4.

Abstract

Human papillomavirus infects millions of people worldwide and is a causal agent of cervical cancer in women. The HPV E2 protein controls the expression of all viral genes through binding of its dimeric C-terminal domain (E2C) to its target DNA site. We engineered monomeric versions of the HPV16 E2C, in order to probe the link of the dimeric beta-barrel fold to stability, dimerization, and DNA binding. Two single-chain variants, with 6 and 12 residue linkers (scE2C-6 and scE2C-12), were purified and characterized. Spectroscopy and crystallography show that the native structure is unperturbed in scE2C-12. The single chain variants are stabilized with respect to E2C, with effective concentrations of 0.6 to 6 mM. The early folding events of the E2C dimer and scE2C-12 are very similar and include formation of a compact species in the submillisecond time scale and a non-native monomeric intermediate with a half-life of 25 ms. However, monomerization changes the unfolding mechanism of the linked species from two-state to three-state, with a high-energy intermediate. Binding to the specific target site is up to 5-fold tighter in the single chain variants. Nonspecific DNA binding is up to 7-fold weaker in the single chain variants, leading to an overall 10-fold increased site discrimination capacity, the largest described so far for linked DNA binding domains. Titration calorimetric binding analysis, however, shows almost identical behavior for dimer and single-chain species, suggesting very subtle changes behind the increased specificity. Global analysis of the mechanisms probed suggests that the dynamics of the E2C domain, rather than the structure, are responsible for the differential properties. Thus, the plastic and dimeric nature of the domain did not evolve for a maximum affinity, specificity, and stability of the quaternary structure, likely because of regulatory reasons and for roles other than DNA binding played by partly folded dimeric or monomeric conformers.

摘要

人乳头瘤病毒在全球感染了数百万人,是导致女性宫颈癌的病原体。人乳头瘤病毒E2蛋白通过其二聚体C末端结构域(E2C)与靶DNA位点结合来控制所有病毒基因的表达。我们构建了HPV16 E2C的单体形式,以探究二聚体β-桶状折叠与稳定性、二聚化及DNA结合之间的联系。纯化并表征了带有6个和12个残基连接子的两种单链变体(scE2C-6和scE2C-12)。光谱学和晶体学表明,scE2C-12中的天然结构未受干扰。相对于E2C,单链变体更加稳定,有效浓度为0.6至6 mM。E2C二聚体和scE2C-12的早期折叠事件非常相似,包括在亚毫秒时间尺度内形成紧密物种以及半衰期为25 ms的非天然单体中间体。然而,单体化将连接物种的去折叠机制从两态变为三态,并伴有一个高能中间体。单链变体与特定靶位点的结合紧密程度提高了5倍。单链变体与非特异性DNA的结合能力减弱了7倍,导致位点识别能力总体提高了10倍,这是目前报道的连接DNA结合结构域中最大的。然而,滴定微量热结合分析表明,二聚体和单链物种的行为几乎相同,这表明在增加的特异性背后存在非常细微的变化。对所探究机制的整体分析表明,E2C结构域的动力学而非结构决定了其不同的特性。因此,该结构域的可塑性和二聚体性质并非为了实现四级结构的最大亲和力、特异性和稳定性而进化,这可能是由于调控原因以及部分折叠的二聚体或单体构象所发挥的除DNA结合以外的其他作用。

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