1. Aims and Hypotheses

We propose to generate and study models of the most fundamental cellular systems, culminating in the creation of the first human-engineered protocell capable of self-sustained activity, and eventually, reproduction and evolution. We intend to study the problem using both experimental and computational approaches. Our experimental goal is to develop simple molecular systems that can carry out the essential life functions of energy capture and storage and protein synthesis. Computationally we will model the couplings between these functions. These studies will guide the integration of the separate molecular subsystems into a laboratory model of a self-maintaining protocell. By combining experimental and theoretical efforts we will explore the principles of non-genomic evolution and its ramifications for the origin of life.

Our main hypothesis is that the emergence of genomically controlled protocells was preceeded by a period during which membrane-bounded, cell-like structures formed and evolved in the absence of coded information storage (e.g the nucleic acid-based systems employed by modern cells). We postulate that the primary metabolic functions of protocells were performed by peptides, the precursors of proteins in contemporary cells. This represents a new view of protocells as structures built of components related to those in contemporary cells, but which function in concert and evolve without a genome.

Our hypotheses will be tested in the laboratory through the construction of peptide protoenzymes that catalyze the reactions used by the protocell for peptide synthesis. A novel application of in vitro selection of biopolymers with desired specificities, applied so far only to nucleic acids, will be employed (see FIGURE 1, FIGURE 2). Once this is accomplished, the protoenzymes will be encapsulated in membrane-bounded structures which contain a simple protein system that can supply the energy needed to drive peptide synthesis (see FIGURE 3). We will demonstrate that, under the appropriate conditions, a community of such non-genomic protocells will be self-sustaining by means of a simple process of growth and reproduction through division. We expect that once protocells acquire the capability to incorporate membrane-forming material into their walls, the community will grow and evolve. To generate viable protocellular systems from an essentially infinite set of possibilities, joint efforts involving laboratory and computer simulation studies will be required.