Synthesis and crystal structure study of 2′-Se-adenosine-derivatized DNA

The selenium derivatization of nucleic acids is a novel and promising strategy for 3D structure determination of nucleic acids. Selenium can serve as an excellent anomalous scattering center to solve the phase problem, which is one of the two major bottlenecks in macromolecule X-ray crystallography. The other major bottleneck is crystallization. It has been demonstrated that the incorporated selenium functionality at the 2′-positions of the nucleosides and nucleotides is stable and does not cause significant structure perturbation. Furthermore, it was observed that the 2′-Se-derivatization could facilitate crystallization of oligonucleotides with fast crystal growth and high diffraction quality. Herein, we describe a convenient synthesis of the 2′-Se-adenosine phosphoramidite, and report the first synthesis and X-ray crystal structure determination of the DNA containing the 2′-Se-A derivatization. The 3D structure of 2′-Se-A-DNA decamer [5′-GTACGCGT(2′-Se-A)C-3′]₂ was determined at 1.75 Å resolution, the 2′-Se-functionality points to the minor groove, and the Se-modified and native structures are virtually identical. Moreover, we have observed that the 2′-Se-A modification can greatly facilitate the crystal growth with high diffraction quality. In conjunction with the crystallization facilitation by the 2′-Se-U and 2′-Se-T, this novel observation on the 2′-Se-A functionality suggests that the 2′-Se moiety is sole responsible for the crystallization facilitation and the identity of nucleobases does not influence the crystal growth significantly.