Putting greenhouse gas mitigation under the microscope

Studying a key enzyme in its native environment

Because it is a membrane metalloenzyme, the methane oxidation activity of pMMO is sensitive to solubilisation and removal from the membrane. From whole cells to isolated membranes, catalytic activity decreases by 5-10-fold, and upon solubilisation in detergent, there is a further 10-fold reduction in activity with no measurable activity for crystallised samples. To fully understand how the enzyme functions, it is important to study it in its native environment, in its most active state in the cell, rather than in soluble single particle or crystal form.

Cell arrangement correlates with increased activity

A team of scientists used cryo-electron tomography (cryo-ET) to determine the structure of pMMO in its native membrane to 4.8 Å resolution. Data was collected at Diamond’s electron Bio-Imaging Centre (eBIC) using the 300kv Titan Krios microscope with technical support from staff scientists at eBIC. The data revealed lipid-stabilised features and a higher-order hexagonal array arrangement in intact cells. Array formation correlates with increased enzymatic activity, highlighting the importance of studying the enzyme in its native environment.

Opening up pathways for improved biotechnology

The remarkable hexagonal arrays of pMMO trimers provide new insights into the impact of higher-order packing on the enzymatic activity of pMMO in native cells. Understanding how pMMO arrays assemble and promote methane oxidation will be integral to future efforts to deploy methanotrophs in biotechnology. The findings also demonstrate the power of cryo-ET to structurally characterise native membrane enzymes in the cellular context.