New research helps explain the pathways for complex chemistry on the primordial earth developing into key biological processes for the origin of life.
By Sam Johnson
Photo courtesy of Pexels from Pixabay.
The question of how life began is one of the great existential ponderings of humankind and scientific research. Before we can answer this we must answer a more foundational question – what is life?
Early philosophising posed some vitalist force or aether that was unique to living things and bestowed the property of life. In modern science, however, the definition is less clean cut, posing instead a spectrum as a functional ability. At one end we have complex, mobile, multicellular life forms with advanced nervous systems allowing for consciousness and intensive processing. At the other end, we have single cellular life, without intentionality, but with the ability to consume food, turn this into energy and reproduce to continue itself by some means. These basic abilities rely on chemical processes, posing the question of when such processes stop being chemistry and become biology, a feature that we would describe as alive.
To answer this foundational question a new study published in science advances explores protein structures that arose in the primordial chemical soup of ancient Earth. Identifying key contenders for some of the first complex molecules that were able to harvest energy, to do work and carry out key chemical reactions is vital for the development of life on this planet. To begin with, the team behind the study decided to start from the premise that life as we know it depends on collecting and using energy. That primordial energy would most likely have come from the skies, in the form of radiation from the Sun, or from deep within the Earth, as heat seeping through hydrothermal vents at the bottom of the ancient seas. On a molecular level, energy use means transferring electrons, the fundamental chemical process which involves an electron moving from one atom or molecule to another. Electron transfer is at the core of oxidation-reduction reactions (also known as redox reactions) that are vital to some of the basic functions of life. Metals are the best elements for carrying out electron transfer, and complex protein molecules are what most biological organisms are made from, driving key processes. Researchers decided to combine the two and search for proteins that bind metals.
A methodical, computational approach was used to compare metal-finding proteins, revealing certain common features that matched across all of them, irrespective of the protein’s functionality, the metal it binds to, or the organism involved. "We saw that the metal-binding cores of existing proteins are indeed similar even though the proteins themselves may not be," says microbiologist Yana Bromberg, from Rutgers University-New Brunswick in New Jersey. “We also saw that these metal-binding cores are often made up of repeated substructures, kind of like Lego blocks. Curiously, these blocks were also found in other regions of the proteins, not just metal-binding cores, and in many other proteins that were not considered in our study." This research suggests such shared features may well have been present and working in the earliest proteins, changing over time to become the proteins we see today whilst keeping certain common structures and core functionality.
Soluble metals in the Archean Ocean covering Earth thousands of millions of years ago could have been used to power the electron shuffling required for energy transfer and, in turn, biological life. "Our observation suggests that rearrangements of these little building blocks may have had a single or a small number of common ancestors and given rise to the whole range of proteins and their functions that are currently available," says Bromberg. "That is, to life as we know it." In particular, the team identified evolutions in protein folding (the shapes formed by proteins as they become biologically active) that may have produced the proteins we know today, like a molecular family tree showing evolution over time.
The study also concludes that biologically functional peptides, the smaller versions of proteins (like individual lego blocks in the structure of proteins) predate the earliest proteins which go back as far as 3.8 billion years ago, adding to our understanding of how life first originated.
The study also concludes that biologically functional peptides, the smaller versions of proteins (like individual lego blocks in the structure of proteins) predate the earliest proteins which go back as far as 3.8 billion years ago, adding to our understanding of how life first originated. Analysis of the beginnings of life on Earth can be important in looking for life on other planets too, where life might begin to evolve (or have already evolved) along similar biological paths. "We have very little information about how life arose on this planet, and our work contributes a previously unavailable explanation," says Bromberg. "This explanation could also potentially contribute to our search for life on other planets and planetary bodies. Our finding of the specific structural building blocks is also possibly relevant for synthetic biology efforts, where scientists aim to construct specifically active proteins anew." This research helps explain how biological processes arose out of complex chemistry in the primordial soup billions of years ago.
