Directed Evolution: Semiconductors Emulating Biology

Enzymes originating from marine sponges were intentionally altered to create a new enzyme that can make semiconductors in artificial cells.

High magnification microscopy images of silica bubbles. — Image courtesy of Daniel Morse

The Science

The first “directed evolution” of an enzyme from marine sponges has been achieved in a cell-free synthetic platform, and the method is capable of synthesizing semiconductors, materials never before produced by living organisms. DNA coding for the silicatein enzyme that catalyzes marine sponge skeleton synthesis was mutated and coupled to polystyrene beads in oil-water emulsions. The oil-water-polymer bubbles act as surrogates of living cells, containing all the biological constituents needed to synthesize semiconductor silicon dioxide (silica) or titanium dioxide (titania) composites.

The Impact

The potential for mimicking biosynthesis as it occurs in nature to the synthesis of high-performance materials has remained a challenge, largely due to the toxicity of these materials to living cells. The success in this research, together with biotechnological capacity to evolve and reengineer enzymes, suggests exciting possibilities for directing enzyme evolution toward the synthesis of new solid-state materials never before produced by living organisms.

Summary

The processes of genetic mutation and natural selection have been accelerated in the laboratory to evolve proteins that catalyze the synthesis of semiconductors in aqueous solutions at low temperature. The critical challenge for mimicking nature’s methods for the synthesis of high-performance materials has always been overcoming the toxicity of these materials to living cells. To address this challenge, research at the University of California–Santa Barbara focused on mutating the DNA coding for the silicatein enzyme that catalyzes marine sponge skeleton synthesis. The resulting DNA strands were introduced into microscopic liquid bubbles, comprised of polystyrene micro beads in oil-water emulsions, which acted as surrogates of living cells. The bubbles contained all the biological constituents needed to express the mutant DNA molecules, synthesize the new silicatein molecules encoded by the DNA mutants, and – for the few new silicateins with exactly the right structure – support the catalytic synthesis of the new semiconductors. High-speed fluorescence laser sorting was used to recognize and select mutants that produced the silicateins capable of catalyzing the synthesis of desired semiconductors. The success of this biotechnology route to semiconductors - materials that have provided a cornerstone for economic and technological growth – opens the door to an exciting new strategy for mimicking the genetic evolution of biology for synthesizing high-performance materials.

Contact

Daniel E. Morse
UC Santa Barbara
[email protected]

Funding

Basic Research: DOE, Office of Science, Basic Energy Sciences (BES) program; L.A.B. was partially supported by University of California System-wide Biotechnology Research and Education Program Graduate Research and Education in Adaptive Bio-Technology Training Grant; J.R.N. was partially supported by a National Science Foundation Graduate Research Fellowship. Research included powder diffraction characterization at the Advanced Photon Source, a BES-supported user facility.

Publications

Lukmaan A. Bawazera, Michi Izumib, Dmitriy Kolodinc, James R. Neilson, Birgit Schwenzer, and Daniel E. Morse, Evolutionary selection of enzymatically synthesized semiconductors from biomimetic mineralization vesicles., Proc. Natl. Acad. Sci., USA, 2012, 109 (26): E1705-E1714. www.pnas.org/cgi/doi/10.1073/pnas.1116958109