Metals enable a non-enzymatic acetyl CoA pathway

Abstract

The evolutionary origins of carbon fixation, the biological conversion of CO2 to metabolites, remain unclear. Phylogenetics indicates that the AcCoA pathway, the reductive fixation of CO2 to acetyl and pyruvate, was a key biosynthetic route used by the Last Universal Common Ancestor (LUCA) to build its biochemistry. However, debate exists over whether CO2 fixation is a relatively late invention of pre-LUCA evolution or whether it dates back to prebiotic chemistry. Here we show that zero-valent forms of the transition metals known to act as co-factors in the AcCoA pathway (Fe0, Ni0, Co0) fix CO2 on their surface in a manner closely resembling the biological pathway, producing acetate and pyruvate in near mM concentrations following cleavage from the surface. The reaction is robust over a wide range of temperatures and pressures with acetate and pyruvate constituting the major products in solution at 1 bar of CO2 and 30 {degrees}g;C. The discovered conditions also promote 7 of the 11 steps of the rTCA cycle and amino acid synthesis, providing a stunning direct connection between simple inorganic chemistry and ancient CO2-fixation pathways. The results strongly sup-port the notion that CO2-fixation pathways are an outgrowth of spontaneous geochemistry.