Team:PacificU-Oregon/Description

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Project Description

The Biology

Basics

Our product's name is Sclerotite, a combination of the word sclerotin and the -ite suffix. Sclerotin is a biocomposite used by arthropods to harden segments of their exoskeleton, thus allowing them to create armor, wings, and other non-soft components. Over the summer, we experimented with different combinations of cuticle proteins and hardening enzymes from various insects, especially our favorite beetle: Tribolium castaneum.

Sclerotin is hardened by crosslinking monomeric protein subunits into a dense, hydrophobic matrix of interlinking proteins. Since the enzymatic systems involved in sclerotin hardening, called tanning, are somewhat complex we chose to use Gibson assembly to construct plasmids that contained multiple operons. A secondary motivation for this is that we need precise control over when the matrix hardens for our product to be viable. To this end, we initially experimented with means to regulate gene expression that were highly digital in nature (we wanted strong "on" and "off" states, rather than being somewhere in between). This alone took up the bulk of our summer.

Mechanism

As mentioned above, sclerotin is a protein matrix that is crosslinked, meaning individual polypeptide chains are covalently or ionic bonded together at internal amino acids to other polypeptide chains directly (such as by the disulfide bond) or indirectly through crosslinking agents. This allows the individual polypeptide chains to form matrices with radically different properties than the individual chains may have. In the case of sclerotin, the individual chains are often hydrophilic and fairly short (300-700 bp on average), but they come together to form hydrophobic and incredibly large matrices.

The specific molecules that crosslink the sclerotin monomers are called quinones, which are the oxidized form of catechols. Quinones are often used in electron transfer reactions, such as those in the electron transport chain in mitochondria. Similarly, quinones transfer electrons to the thiol group on sclerotin monomers allowing them to form bonds to other thiol groups. By far, the controlled synthesis of the correct quinones has been the most difficult part of our project and ultimately held us back from getting as much progress as we anticipated.

Difficulties

Our team has struggled in two main ways: we suffered low transformation efficiency in our bacterial transformation, and we had trouble controlling the synthesis of quinones. Our low transformation efficiency was most likely due to our lack of wisdom and experience in transforming bacteria with large scale plasmids (our largest was 15 kb, and we will be working with two at 10 kb each directly after iGEM as our project will continue). Quinone synthesis issues were more complex. We are still not sure if our enzyme pathway is not producing the quinones we are expecting, if those quinones are not tanning our monomers, or if we are missing some critical ligand required for tanning that has not yet been reported in the literature. Information on the tanning process is limited at best, which added both to the difficulty and fun of this project.

The Motivation

Environmental Cost of Concrete

Concrete comes with some serious environmental and financial cost. Cement requires calcium carbonate to be thermally decomposed at extremely high temperatures, which both takes a large amount of energy and produces a fair fraction of humanity's CO₂ output. Sclerotite could remedy this by both being cheap to produce exclusively at ambient temperatures rather than high-heat environments and being a carbon-negative building material (CO₂ is fixed as Sclerotite is produced).

More and More and More People!

Our planet is poised to soon house over 8 billion people, a nearly unfathomable number. To house all of these people in two-person, 800 square foot apartments, we would have to build an additional 188,600 Empire State Buildings worth of apartments. Current concrete production will not be able to keep up with the increased demand for residential space, especially with the massive influx of people into cities. However, Sclerotite could be grown on algae farms even on non-arable land (so it doesn't compete with existing agriculture).

As it always has, technology will be the solution to our global problems. We believe Sclerotite will pave the way to a sustainable ecosystem of high-density architecture in the future.

The Future

We didn't get nearly as far as we wanted to this summer due to complications mentioned in the Difficulties subsection, but that isn't stopping us. We will continue developing Sclerotite until it is a consumer product ready for mass market use. We won a business fellowship through the Inspired Ideas Competition at Pacific University's Berglund Center, which will provide further funding and a platform to continue work on Sclerotite and eventually develop a marketing plan for it.

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