Structural effects of chirally mutated Enkephalin neurotransmitters: An argument for biological homochirality

• Systematic study of structure and non-covalent interactions afforded by chirally substituted Ala(2)-Leu- Enkephalins.
• Chiral substitutions are shown to drastically alter structure and intermolecular interactions afforded by these peptides.
• An organism based on homochiral polymers has a much higher evolvability than an organism based on heterochiral polymers.

In living organisms all peptides and proteins used endogenously are homochiral. However, heterochiral peptides, formed by post-translational modifications in some species, are used exclusively exogenously. These puzzling facts, accomplished at significant metabolic cost, are investigated here. A systematic study of the effect of chiral substitutions on structure and non-covalent interactions afforded by Ala(2)-Leu-Enkephalins by a combination of mass spectrometry/ion mobility spectrometry and techniques of computational chemistry is reported. The data show that chiral substitutions of amino acid residues have drastic consequences for peptide structure and their interactions as gauged by self- and cross assembly. Our data suggest that an organism based on homochiral polymers has a much higher evolvability than an organism based on heterochiral polymers.

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