NASA Astrobiology Institute (NAI)

This project addresses the functions of an ancient protein family in Archaea that occupy extreme environments. Some of these proteins may play roles similar to those of comparable proteins in other living organisms, and thus may tell us about functions that evolved in the last universal common ancestor of life. Others may have evolved as the Archaea began to occupy specialized and often extreme environments. This project also addresses the emergence of proto-metabolic networks that supplied the precursors for the RNA World.

Functions of an Ancient Protein Family in Archaea: Thioredoxins (Trxs) are found in all forms of life, and therefore must have been present in the LUCA. Trxs serve three functions: 1) reduction of disulfides formed at the active sites of enzymes during turnover; 2) reduction of regulatory disulfide bonds in proteins; and 3) participation as a structural component of protein complexes. Trxs provide an excellent system for studying divergence of protein function as organisms diversified to occupy different ecological niches. An enormous piece of the puzzle is missing, however, because we know nothing about the functions of Trxs in Archaea. We are studying Trxs in Halobacterium sp. NRC-1, an extreme halophile that grows in environments that contain very high salt, are exposed to intense sunlight, fluctuate between oxic and anoxic conditions, and are often contain toxic heavy metals. Halobacterium sp. NRC-1 contains six Trxs. We will capture target proteins for each Trx using mutant forms of each protein that can attach to target proteins but cannot release them. Target proteins will be identified by mass spectrometry. We have cloned and purified all six Trxs, as well as three potential target proteins. We have generated two mutant Trxs, and are currently generating the other four mutants.

The Origin of the RNA World: Dr. Copley, Eric Smith (Santa Fe Institute), and Harold Morowitz George Mason University) have proposed a mechanism by which mutual catalysis in a pre-biotic network initiated a progression of stages characterized by ever larger and more effective catalysts supporting a proto-metabolic network, leading ultimately to the RNA World. This work was published in 2007. We are currently working on a paper exploring the role of sparseness in proto-metabolic networks that laid the foundation for emergence of the RNA World.