Genomics and Cell Biology: March 2012

A team of researchers from NAI's Montana State University Team has proposed a new path in the evolution of biological nitrogen fixation on Earth. Nitrogen is one of the most important elements for life on Earth, and astrobiologists have long been interested in its role in the history and evolution of life.

Nitrogen is abundant on our planet as an atmospheric gas. However, in order for Nitrogen to be accessible for life, it must be converted into other chemical forms. A key step in the global cycling of nitrogen is biological nitrogen fixation, which is accomplished via a protein known as 'nitrogenase.' Three forms of nitrogenase are known - all similar, but containing slightly different metallic complexes. Previously, scientists thought the most common nitrogenase found today (which contains the element molybdenum (Mo)) appeared later in life's evolution that the two lesser-found forms (containing vanadium (V) or iron(Fe)). The new study has revealed an evolutionary path that places Mo-dependent nitrogenase earlier than the V and Fe forms. The study is changing views of how this important biological pathway evolved through time - shedding light on the early history of life on Earth.

The study was published in the journal Frontiers in Microbiology under lead author Eric S. Boyd. The research was carried out as part of the NAI project "Evolution of Nitrogen Fixation, Photosynthesis, Hydrogen Metabolism, and Methanogenesis."

Date/Time: Monday, March 5, 2012 11:00 AM Pacific

Presenter: Michael Hecht (Princeton University)

Abstract: The entire collection of genes and proteins in all the living systems on earth comprises a minuscule fraction of sequence space. From the enormous diversity of possible gene and protein sequences, billions of years of evolution selected only a very small collection of "molecular parts" that sustain living organisms (only ~4,000 genes in E. coli and ~20,000 in humans.) These considerations might lead to an assumption that the sequences that enable life are unusual or special. Is this true? Or can sequences designed from scratch sustain the growth of living cells?

To address these questions, we designed and constructed a collection containing millions of artificial proteins (a model 'proteome') encoded by a library of synthetic genes (an artificial 'genome'). Structural studies show that many (perhaps most) of our novel proteins fold into stable 3-dimensional structures. Next, we used genetic selections to demonstrate that several of these novel proteins provide biochemical functions that are essential for the growth of E. coli. Thus, artificial sequences, which never before existed on earth, possess activities that sustain life.

This initial foray into artificial genomics suggests (i) the molecular toolkit for life need not be limited to genes and proteins that already exist on earth; (ii) the construction of artificial genomes composed of non-natural sequences is within reach; and (iii) it may be possible to devise synthetic organisms that are sustained by de novo designed proteins encoded by novel genomes.

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