British scientists write in the latest issue of the Proceedings of the National Academy of Sciences that they have discovered the origin of the protein structure responsible for the metabolism of life on Earth, these simple molecules provided the power for early life on Earth, and can act as a chemical signal that teams such as NASA can use to search for life on other planets.

In a new study, scientists from Rutgers University's "Evolution of nanomachine in the Geosphere and Microbial Ancestors" (ENIGMA) team traced the evolution of enzymes (proteins) from now to long ago, and found the first two metabolic proteins in the evolution of life 3.5 billion to 2.5 billion years ago. The ENIGMA project aims to reveal the role of the simplest proteins that catalyze the earliest stages of life.

In the latest study, the ENIGMA team looked at two protein "folds" : the ferridoxin fold, which binds to iron-sulfur compounds, and the Rossman fold, which binds to nucleotides (the building blocks of DNA and RNA). They believe that these two folds are likely the earliest structures of early metabolism. And, there is evidence that these two folds may share a common ancestor. If true, this ancestor may have been the first enzyme to metabolize life on Earth.

The researchers explain that proteins are chains of amino acids, and their 3D paths through space are called folds. Ferredoxin is a metal found in modern proteins that shuttles electrons around cells to boost metabolism. Electrons flow through solids, liquids and gases and power living systems, and the same amount of electricity must exist in other planetary systems for life to thrive.

ENIGMA principal investigator Paul G. Falkowski said: "We believe that life is made up of very small parts that then make cells and eventually organisms as complex as humans. Now we have found the building blocks of life, the building blocks that ultimately led to the evolution of cells, animals and plants."

Study co-author Vikas Nanda, a professor of biochemistry and molecular biology, said: "We know very little about how life began on Earth, and this latest study gives us insight into and the discovery of the earliest metabolic proteins."

The researchers will conduct laboratory tests to better understand the origin of life on Earth and, hopefully, how life began on other planets.