Origin of biomolecular homochirality
Life’s molecular machinery is homochiral: all living systems use just one mirror-image of molecules. How did this happen?
Biomolecules, such as amino acids and sugars, exist as mirror-image pairs, or enantiomers, which is the property of chirality. In the absence of a driver to induce one chiral form, abiotic synthesis of these molecules results in an equal mixture of left- and right-handed forms, or a racemic mixture. Interestingly, biological systems exclusively use one enantiomer: amino acids are left-handed, while nucleic acids and sugars are right-handed—making biological systems homochiral.
This fundamental characteristic raises the question of how life on Earth acquired homochirality, which Science magazine has ranked among the 125 most significant scientific questions! Our research group is interested in this big question, first sparked by Pasteur's discovery of biomolecular homochirality more than 175 years ago.
We have demonstrated that a relatively recently discovered phenomenon in physics—chiral-induced spin selectivity (CISS)—can account for life's chiral selectivity. CISS involves the strong coupling of electron spin to molecular chirality, enabling achiral magnetized surfaces to function as chiral agents via spin-controlled asymmetric interactions.
By using magnetic mineral surfaces, like magnetite (Fe3O4), as asymmetric templates for the crystallization of ribose-aminooxazoline (RAO), a central RNA precursor, we have paved the way for the formation of homochiral RNA. Additionally, based on experimental findings, we have proposed a mechanism for transferring RNA's homochirality to peptides and subsequently to metabolites, thereby addressing the opposite handedness of D-nucleic acids and L-peptides in biological systems.
Our results, for the first time, have demonstrated a plausible pathway to achieve a homochiral prebiotic network from fully racemic starting materials, through a robust and novel mechanism.
We are now set to finish the challenge and refine the scenario on which we have already made great progress. Next, we are excited to work with natural materials and chemically heterogeneous mixtures. Moreover, we aim to experimentally verify a feedback mechanism between magnetic surfaces and chiral molecules that can spontaneously self-amplify to a homochiral state, even in the absence of an external field. Furthermore, our proposal for achieving network-wide homochirality could be extended to involve many other compounds, including phospholipids. Studying the spin-controlled asymmetric synthesis of prebiotic compounds on magnetic mineral surfaces is yet another challenge.
The homochirality problem of life—and the role of magnetization in this challenge—offers rich avenues of research with many potential breakthroughs and real-world applications.