2001 Annual Science Report
NASA Ames Research Center Reporting | JUL 2000 – JUN 2001
Early Metabolic Pathways
Early Metabolic Pathways (dm)
The main, long-term goals of this work have been (a) to develop protein enzymes representative of those that existed on the early Earth, (b) to couple their catalytic activity in model protocells to external sources of energy and nutrients, and© to determine conditions under which such protocellular systems can evolve using theoretical modeling.
Functional proteins that efficiently bind adenosine triphosphate (ATP), selected from a very large library of random sequences, have been characterized in detail. It appears that these proteins form folded structures. They were shown to be highly selective â?? they bind ATP but not guanosine triphosphate or cyclic ATP. They require zinc ions, but not magnesium ions, to function and contain conserved cysteine residues. This suggests that their structure may be similar to those of zinc finger proteins.
A simple bioenergetics system consisting of bacteriorhodopsin and ATP synthetase incorporated into phospholipid liposomes was coupled to thermophilic ADP-forming acetyl-CoA synthetase, which in the presence of acetate, CoA and magnesium ions produces acetyl-CoA and converts ATP back to ADP, leading to a light-dependent accumulation of acetyl-CoA. The conditions for maximum production of acetyl-CoA were optimized.
It was demonstrated through theoretical modeling that proteins in protocells could not only grow but in the process yield distributions of catalytic efficiencies quite different that the starting distributions. This is the first example of protocellular evolution in the absence of a genome. The model was extended to include peptide activation and activated ligation. These extensions increased the rate of growth in the catalytic potential of the protocell, as well as the maximum length of peptides produced. This suggests that protocells capable of capturing and storing energy and then using that energy to activate peptides for further polymerization might have been able to increase their catalytic potential rapidly.
PROJECT MEMBERS:Andrew Pohorille
RELATED OBJECTIVES:Objective 2.0
Develop and test plausible pathways by which ancient counterparts of membrane systems, proteins and nucleic acids were synthesized from simpler precursors and assembled into protocells.
Replicating, catalytic systems capable of evolution, and construct laboratory models of metabolism in primitive living systems.