Since the industrial revolution, humans have been releasing massive amounts of greenhouse gases into the atmosphere, and these gases have been causing rapid increases in global temperature and changes in global climate. The most notoriously known industrially produced greenhouse gas is CO2. Sustainable development efforts have often focused on reducing CO2 emissions through developing alternative energy sources such as electricity, solar power, and ethanol fuel, often against the endless whining of corporate-funded republican “climate skeptics” in the US. However, there is another potential method of sustainable development, one that focuses on neutralizing or “sequestering” CO2 from industrial factories before they are released into the atmosphere. This can be done by simply capturing the CO2 waste generated from factories and chemically converting it into a harmless compound, which, theoretically, shouldn’t be too hard since we have an enzyme in our body that does just that.
Carbonic anhydrase (CA), an enzyme produced in just about every major group of organisms on Earth, catalyzes the reaction:
Image from madscienceblogs
This converts CO2 into bicarbonate (HCO3–), and, if used industrially, can eliminate greenhouse gas produced from fossil fuel combustion. CA is so ubiquitous in all branches of the tree of life because its function is useful for many different purposes. In our body, CA is used to maintain a stable PH by stabilizing H+ concentrations while in plants, the same enzyme is used to increase CO2 concentrations to increase the efficiency of photosynthesis.
Carbonic andyrase functions with a zinc ion in its active site. (Image from wikipedia)
An enzyme that is to be used to sequester CO2 waste from fossil fuel combustion must be stable in high temperature conditions, which is intolerable to the CA in our bodies. However, a research team in the University of Florida sought to use a newly discovered version of CA in the deep-sea bacteria thiomicrospira crunogena to sequester industrial CO2, called TcruCA for short. T. crunogena is a chemoautotroph that lives near hydrothermal vents, and uses CA to help with uptake of inorganic carbon-containing compounds. TcruCA has evolved to withstand temperatures much higher that it’s counterpart in our bodies, and is a good candidate for CO2 sequestering.
Video from University of Florida
In order to successfully sequester industrial CO2 with TcruCA, the enzyme must first be must be mass-produced, which could be done by splicing the gene that codes for this enzyme into E coli cells, which would then be used to express TcruCA. Next, a filter system must be designed so that as waste gases from fossil fuel combustion pass through, the TcruCA inside converts the CO2 inside into bicarbonate. Keep in mind that this reaction is an equilibrium reaction, so the bicarbonate must be further processed into other compounds to continually shift the reaction towards consuming more CO2.
However, there is a problem with TcruCA. It may be more stable than the CA in our bodies, but it is also ten times less efficient. To produce an enzyme ready for industrial use, the efficiency of TcruCA must be enhanced. This could potentially be done through in vitro evolution, which basically means breeding and domesticating the enzyme. First we would generate a huge library of TcruCA using an error-prone process so that each enzyme is a variant with a slightly different amino acid sequence. We would then screen our library for ones that have slightly increased function, while still maintaining their thermostability (those tend to be evolutionary trade-offs). We would then repeat our cycle of “reproduction and selection” until we get an enzyme that’s both stable and efficient.
With carbonic anhydrase, we could reduce greenhouse gas emission while burning fossil fuel at the same time. Don’t get me wrong though, CO2 sequestration is only one of many ways to achieve sustainability and alternative energy is still important and deserves much heavy focus both by scientists and government agencies. However, greenhouse gas sequestration is one way to achieve sustainability without sending many republicans into panic mode about losing some money over saving the environment.