Nearly 50 years since its potential as a fluorescent base analogue was first recognized, 2-aminopurine (2AP) continues to be the most widely used fluorescent probe of DNA structure and the perturbation of that structure by interaction with enzymes and other molecules. In this review, we begin by considering the origin of the dramatic and intriguing difference in photophysical properties between 2AP and its structural isomer, adenine; although 2AP differs from the natural base only in the position of the exocyclic amine group, its fluorescence intensity is one thousand times greater. We then discuss the mechanism of interbase quenching of 2AP fluorescence in DNA, which is the basis of its use as a conformational probe but remains imperfectly understood. There are hundreds of examples in the literature of the use of changes in the fluorescence intensity of 2AP as the basis of assays of conformational change; however, in this review we will consider in detail only a few intensity-based studies. Our primary aim is to highlight the use of time-resolved fluorescence measurements, and the interpretation of fluorescence decay parameters, to explore the structure and dynamics of DNA. We discuss the salient features of the fluorescence decay of 2AP when incorporated in DNA and review the use of decay measurements in studying duplexes, single strands and other structures. We survey the use of 2AP as a probe of DNA-enzyme interaction and enzyme-induced distortion, focusing particularly on its use to study base flipping and the enhanced mechanistic insights that can be gained by a detailed analysis of the decay parameters, rather than merely monitoring changes in fluorescence intensity. Finally we reflect on the merits and shortcomings of 2AP and the prospects for its wider adoption as a fluorescence-decay-based probe.

中文翻译：

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2-氨基嘌呤作为 DNA 构象和 DNA-酶界面的荧光探针

自从首次发现其作为荧光碱基类似物的潜力近 50 年以来，2-氨基嘌呤 (2AP) 仍然是最广泛使用的 DNA 结构荧光探针，并且通过与酶和其他分子的相互作用来扰动该结构。在这篇综述中，我们首先考虑 2AP 与其结构异构体腺嘌呤之间在光物理性质上的巨大而有趣的差异的起源。虽然2AP与天然碱的区别仅在于环外胺基的位置，但其荧光强度却大了一千倍。然后，我们讨论了 DNA 中 2AP 荧光的碱基间猝灭机制，这是其用作构象探针的基础，但仍未完全了解。文献中有数百个使用 2AP 荧光强度变化作为构象变化分析基础的例子。然而，在本次审查中，我们将仅详细考虑一些基于强度的研究。我们的主要目标是强调时间分辨荧光测量的使用，以及荧光衰减参数的解释，以探索 DNA 的结构和动力学。我们讨论了 2AP 在 DNA 中的荧光衰减的显着特征，并回顾了衰减测量在研究双链体、单链和其他结构中的用途。我们调查了使用 2AP 作为 DNA-酶相互作用和酶诱导扭曲的探针，特别关注其用于研究碱基翻转和通过详细分析衰变参数获得的增强机制见解，而不仅仅是监测荧光强度的变化。最后，我们反思了 2AP 的优点和缺点以及其作为荧光衰减探针更广泛采用的前景。