CHIRAL DISCRIMINATION IN DNA - PEPTIDE INTERACTIONS INVOLVING CHIRAL DNA MESOPHASES - A GEOMETRIC ANALYSIS

The notion that ''L-proteins interact more avidly (than D-proteins) wi th D-nucleic acids'' (Hegstorm, R. A.; Kondepudi, D. K. Sci. Am. 1990, 253, 98-105) represents a direct extension to the concept of stereoch emical complementarity. This notion, considered as a central tenet to theories concerned with the origin of biochemical homochirality, is ho wever completely refuted by currently available experimental data that indicate identical DNA affinities towards L- and D-peptides. Here we show that chiral discrimination in nucleic acid-peptide interactions n ecessitates a substantial amplification of macromolecular geometric co nstraints. Thus, DNA molecules are found to exhibit a higher affinity toward L-peptides-but only under conditions that enhance their chiral identity by promoting the formation of cholesteric DNA mesophases. The results allow for new reflections on the concept of molecular complem entarity, and indicate that spontaneously obtained chiral DNA mesophas es might have played a key role in determining the terrestrial L-homoc hirality of proteins. Moreover, the observations provide an intriguing example to the notion that new properties of DNA molecules emerge in their condensed state, in which a higher structural order is imposed.