Theory of chiral recognition in DNA condensation

Collapse of long chiral A-macromolecules assisted by a chiral B-additive (where B associates with A) is considered theoretically. Based on a simple model we demonstrate that the compaction activity of B molecules can strongly depend on the sense of their chirality. The theory is applied to the DNA compaction in the presence of conformationally rigid divalent enantiomeric cations (SS and RR enantiomers).(1) It is shown that both chiral isomers of the dications adsorb well on the DNA surface, but the SS- and RR-binding energies are different, reflecting their unequal stereo-complementarities (the 'bolt-and-nut' effect). Unexpectedly, we find that the compaction activity of less strongly bound SS dication is significantly higher than that of its RR enantiomer. Moreover, the RR molecules tend to replace the SS enantiomers adsorbed on the DNA, so that SS compaction ability is significantly reduced in the presence of RR isomers. The theory thus provides a basis for explanation of recently observed dramatic stereoisomeric selectivity and antagonistic effects in DNA compaction.(1) The revealed chiral discrimination effects may serve as selection mechanisms leading to natural homochirality.