Engineering copper enzymes for hydrocarbon oxidation

Methane, the primary component of natural gas, is a cheap and abundant feedstock that is costly to transport and requires significant capital expenditures to convert to higher value products. As a result, natural gas produced in remote locations such as the Bakken Shale is flared leading to over 18 billion dollars worth of methane being wasted per year. One solution to prevent this waste is to use biological systems for methane conversion.

In nature, methane is aerobically oxidized by bacteria known as methanotrophs, which utilize it for energy production and carbon fixation. Methane enters the methanotroph metabolic pathway by the action of methane monooxygenases (MMOs), which oxidize methane to methanol. Nature employs two types of MMOs: soluble MMO (sMMO), which utilizes a diiron cofactor and particulate MMO (pMMO), which utilizes a dicopper cofactor. One major issue limiting the development of biological gas-to-liquid technology is the inability to express sMMO or pMMO in an industrially relevant host organism.

One approach to this problem is via the computational protein design of scaffold proteins. The active sites of both sMMO and pMMO enzymes were used as inspiration and computationally recapitulated inside scaffold proteins already known to bind copper and express recombinantly in E. coli. Variants from this work have demonstrated the ability to oxidize propylene, a substrate typically used to monitor natural MMO activity.