Universal Sequence Replication, Reversible Polymerization and Early Functional Biopolymers: A Model for the Initiation of Prebiotic Sequence Evolution

Many models for the origin of life have focused on understanding how evolution can drive the refinement of a preexisting enzyme, such as the evolution of efficient replicase activity. Here we present a model for what was, arguably, an even earlier stage of chemical evolution, when polymer sequence diversity was generated and sustained before, and during, the onset of functional selection. The model includes regular environmental cycles (e.g. hydration-dehydration cycles) that drive polymers between times of replication and functional activity, which coincide with times of different monomer and polymer diffusivity. Template-directed replication of informational polymers, which takes place during the dehydration stage of each cycle, is considered to be sequence-independent. New sequences are generated by spontaneous polymer formation, and all sequences compete for a finite monomer resource that is recycled via reversible polymerization. Kinetic Monte Carlo simulations demonstrate that this proposed prebiotic scenario provides a robust mechanism for the exploration of sequence space. Introduction of a polymer sequence with monomer synthetase activity illustrates that functional sequences can become established in a preexisting pool of otherwise non-functional sequences. Functional selection does not dominate system dynamics and sequence diversity remains high, permitting the emergence and spread of more than one functional sequence. It is also observed that polymers spontaneously form clusters in simulations where polymers diffuse more slowly than monomers, a feature that is reminiscent of a previous proposal that the earliest stages of life could have been defined by the collective evolution of a system-wide cooperation of polymer aggregates. Overall, the results presented demonstrate the merits of considering plausible prebiotic polymer chemistries and environments that would have allowed for the rapid turnover of monomer resources and for regularly varying monomer/polymer diffusivities

Current Applications of Artificial Metalloenzymes and Future Developments

International audienceIn between traditional homogeneous metal catalysts and enzyme catalysts, a new class of hybrid catalysts named artificial metalloenzymes resulting from the controlled embedding of transition metal species (ions, synthetic inorganic or organometallic complexes) within natural, genetically-engineered or even de novo protein scaffolds currently undergoes a tremendous development at the academic level. This family of hybrid assemblies ideally combines the features of their individual components, allowing a wide range of chemical reactions, including new-to-nature reactions, to be catalyzed under mild, eco-compatible conditions with high chemo-and/or stereoselectivity. This chapter intends to summarize the most remarkable achievements in artificial metalloenzyme design and properties with emphasis put on industrially relevant chemical reactions, including oxidations, imine reductions, CC and C-N bonds formation. It also gives an up-to-date survey on the most advanced applications of artificial metalloenzymes in cascade reactions and in vivo catalysis