Methanogenesis is the biological production of methane and is utilized by methanogenic archaea (methanogens) to generate energy. This process is responsible for 70% of total atmospheric methane, a potent greenhouse gas and an important energy source (natural gas). In the future, reversing methanogenesis in an engineered methanogenic strain could be realized to efficiently convert natural gas into liquid fuels.
Methyl coenzyme M reductase (Mcr) catalyzes the final reaction of methanogenesis in methanogens and the first reaction in the anaerobic oxidation of methane (AOM) carried out by the anaerobic methanotrophs (ANME). Cofactor F<sub>430</sub>, a unique nickel-containing tetrapyrrole, serves as the prosthetic group and catalytic component of Mcr. Recently, multiple F<sub>430</sub> variants have been discovered in several methanogenic species, including Methanococcus maripaludis, Methanosarcina acetivorans, and Methanocaldococcus jannaschii. A novel variant reported here has an exact mass of 1008.3478, a similar absorption spectrum as unmodified F<sub>430</sub>, and associates with purified Mcr from M. acetivorans. Based on the exact mass, this molecule is likely modified with a mercaptopropamide moiety. In some conditions, this modified F<sub>430</sub> comprises 30-50% of the total F<sub>430</sub> pool.
We also report upon our work to identify the sulfur insertion enzyme required to produce methylthio-F<sub>430</sub> that functions with Mcr in ANME-1. We hypothesized that the insertion of the methylthio moiety is likely catalyzed by a methylthiotransferase (MTTase) homolog present in ANME. However, purified ANME MTTase does not appear to catalyze this reaction, and instead catalyzes the methylthiolation of N6-threonylcarbamoyladenosine (t6A) in tRNA. / Master of Science in Life Sciences / Methanogens are a unique but diverse group of microorganisms that produce methane to generate their energetic needs. The byproduct of their metabolism is methane gas, most of which escapes into the atmosphere. Methanogens produce 70% of Earth's atmospheric methane, which is a gas that has contributed to 20% of global warming since the start of the industrial era. However, methane, which makes up the majority of natural gas, is also an important source of energy, and natural gas generates 40% of the United States' electricity. An issue with natural gas is, as a gas, it readily leaks out in the extraction and transport process. A solution to this is to convert the gas into liquids, which do not display these negatives. It is possible, through a better understanding of how methanogens work, we could produce a methanogen strain that can efficiently convert methane into liquid fuels.
The last methane-generating step in methanogenic metabolism uses a protein known as methyl-coenzyme M reductase (Mcr). To do this, Mcr uses a small molecule known as cofactor F<sub>430</sub>. Recently, variants of the standard F<sub>430</sub> structure have been described, in both methanogens as well as another microbial group known as the anaerobic methanotrophs (ANME). ANME generate their energy through reversing methanogenic metabolism. The work here involves studying why and how methanogens and ANME make F<sub>430</sub> variants. The hope is this work will reveal either different functionalities of cofactor F<sub>430</sub> not previously known, or that they influence Mcr catalysis, potentially in the reverse (methane degradation) direction.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/111130 |
| Date | 05 July 2022 |
| Creators | Boswinkle, Kaleb Storm |
| Contributors | Biochemistry, Allen, Kylie Dawn, Mevers, Emily Elizabeth, Mukhopadhyay, Biswarup |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | ETD, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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