Lescrinier E, Esnouf R, Schraml J, Busson R, Heus H, Hilbers C, Herdewijn P
Laboratory of Medicinal Chemistry, Rega Institute for Medical Research, Katholieke Universiteit Leuven, Leuven, Belgium.
Chem Biol. 2000 Sep;7(9):719-31. doi: 10.1016/s1074-5521(00)00017-x.
Synthetic nucleic acid analogues with a conformationally restricted sugar-phosphate backbone are widely used in antisense strategies for biomedical and biochemical applications. The modified backbone protects the oligonucleotides against degradation within the living cell, which allows them to form stable duplexes with sequences in target mRNAs with the aim of arresting their translation. The biologically most active antisense oligonucleotides also trigger cleavage of the target RNA through activation of endogenous RNase H. Systematic studies of synthetic oligonucleotides have also been conducted to delineate the origin of the chirality of DNA and RNA that are both composed of D-nucleosides.
Hexitol nucleic acids (HNA) are the first example of oligonucleotides with a six-membered carbohydrate moiety that can bind strongly and selectively to complementary RNA oligomers. We present the first high resolution nuclear magnetic resonance structure of a HNA oligomer bound to a complementary RNA strand. The HNA-RNA complex forms an anti-parallel heteroduplex and adopts a helical conformation that belongs to the A-type family. Possibly, due to the rigidity of the rigid chair conformation of the six-membered ring both the HNA and RNA strand in the duplex are well defined. The observed absence of end-fraying effects also indicate a reduced conformational flexibility of the HNA-RNA duplex compared to canonical dsRNA or an RNA-DNA duplex.
The P-P distance across the minor groove, which is close to A-form, and the rigid conformation of the HNA-RNA complex, explain its resistance towards degradation by Rnase H. The A-form character of the HNA-RNA duplex and the reduced flexibility of the HNA strand is possibly responsible for the stereoselectivity of HNA templates in non-enzymatic replication of oligonucleotides, supporting the theory that nucleosides with six-membered rings could have existed at some stage in molecular evolution.
具有构象受限糖-磷酸骨架的合成核酸类似物广泛应用于生物医学和生化应用的反义策略中。修饰后的骨架可保护寡核苷酸在活细胞内不被降解，使其能够与靶mRNA中的序列形成稳定的双链体，从而阻止其翻译。生物活性最强的反义寡核苷酸还可通过激活内源性核糖核酸酶H触发靶RNA的切割。人们还对合成寡核苷酸进行了系统研究，以阐明均由D-核苷组成的DNA和RNA手性的起源。
己糖醇核酸（HNA）是具有六元碳水化合物部分的寡核苷酸的首个实例，它能够与互补RNA寡聚物强烈且选择性地结合。我们展示了与互补RNA链结合的HNA寡聚物的首个高分辨率核磁共振结构。HNA-RNA复合物形成反平行异源双链体，并采用属于A型家族的螺旋构象。可能由于六元环刚性椅式构象的刚性，双链体中的HNA和RNA链都具有明确的定义。观察到的无末端磨损效应也表明，与经典双链RNA或RNA-DNA双链体相比，HNA-RNA双链体的构象灵活性降低。
小沟中的P-P距离接近A型，且HNA-RNA复合物的刚性构象解释了其对核糖核酸酶H降解的抗性。HNA-RNA双链体的A型特征以及HNA链灵活性的降低可能是HNA模板在寡核苷酸非酶复制中具有立体选择性的原因，这支持了六元环核苷可能在分子进化的某个阶段存在的理论。
