Racemic crystal structures of A-DNA duplexes
Pradeep K. Mandal, Gavin W. Collie, Brice Kauffmann and Ivan Huc [1]
Molecular Tour
Racemic mixtures of naturally chiral macromolecules demonstrated a strong propensity to form racemic crystals. Theoretical suggestions and experimental observations support easier crystallogenesis than for single enantiomers, as well as denser packing and better diffraction. Previous studies revealed that the structures determined from racemic DNA mixtures were nearly identical to those from D-enantiopure solutions. In this article, we report the discovery of additional conformational state of the DNA hexamer D/L-d(CCCGGG) in two centrosymmetric crystal forms R3− and P21/n. of d(CCCGGG)2 into hetero-chiral pseudo-helices within the lattice of crystal form R3−. An almost identical pattern is observed in crystal form P21/n.
In the D-enantiopure solution with high salt content, the d(CCCGGG) forms Z-DNA duplex while in the racemic mixture with high salt content D/L-d(CCCGGG) formed an A-DNA duplex. Solution studies of this sequence in Z-DNA and A-DNA crystallization conditions showed that the prevalent species is B-DNA. The two crystal forms of D/L-d(CCCGGG) revealed novel hetero-chiral pseudo-continuous helices where a D-d(CCCGGG) duplex and a L-d(CCCGGG) duplex stack end-to-end in an alternating manner, with an inversion of helix handedness at every helix-helix contact. The study suggests that racemic mixtures of DNA sequences may generate assemblies and higher-order structures not accessible to equivalent enantiopure systems.
References
- ↑ Mandal PK, Collie GW, Kauffmann B, Huc I. Racemic crystal structures of A-DNA duplexes. Acta Crystallogr D Struct Biol. 2022 Jun 1;78(Pt 6):709-715. doi:, 10.1107/S2059798322003928. Epub 2022 May 9. PMID:35647918 doi:http://dx.doi.org/10.1107/S2059798322003928
