THE EVOLUTION OF “BIOLOGICAL” MINERALS AND THE ORIGIN OF LIFE (Invited Presentation)

Life is electric. To extract energy from the environment, life evolved a series of enzymes (oxidoreductases) that transfer electrons along redox gradients to form metabolic pathways. These processes ultimately gave rise to changes in the gas composition of Earth’s atmosphere. The oxidoreductases involved in electron transfers invariably contain one or more transition metals, of which iron is, by far, the most prevalent. Many transition metals bound in oxidoreductases resemble natural minerals. For example, one of oldest and most commonly occurring metal sites is a 4Fe4S cluster which closely resembles greigite. Although the mineral may have been incorporated directly from the environment into peptides prior to the origin of life, in all extant organisms the cluster is formed biologically in a variety of metabolic pathways. One of the most geochemically important metal clusters is a 4 Mg, 1 Ca “cubane” which mediates photocatalytic water splitting in Photosystem II and is found in all oxygenic photosynthetic organisms. In contrast to the 4Fe4S cluster, the 4Mn1Ca cubane has no known analog in natural minerals; it appears to be solely formed as a “biological” mineral and its evolutionary history is very poorly understood. Indeed, how life evolved to synthesize many of these metal clusters remains largely unknown. Regardless, the evolution of biological metabolism, which is how life extracts energy from the environment, requires an understanding of “biomineral” formation. This talk will examine how we approach the intersection of biological electron transfer reactions, the availability of transition metal minerals across geologic time, and the evolution of life.