Research Areas

Biological Methane Oxidation

Biological Methane Oxidation

Left, transmission electron micrograph of Methylosinus trichosporium OB3b cells. The bundled membrane structures at the periphery house pMMO. Right, crystal structure of the Methylocystis sp. strain Rockwell pMMO protomer. The PmoB subunit is shown in purple, the PmoA subunit is shown in blue, the PmoC subunit is shown in gray, and an unidentified helix is shown in orange. Copper ions are shown as cyan spheres and lipids are shown as green sticks.

Methanotrophic bacteria oxidize methane to methanol in the first step of their metabolic pathway. Methane is a potent greenhouse gas, with a global warming potential more than 84 times that of carbon dioxide over a 20 year period. Global warming presents a significant threat to human health, and as the only biological methane sink, methanotrophs have attracted much attention as a means of mitigating methane emissions. Moreover, increasing natural gas reserves combined with an ongoing price spread between natural gas and gasoline have led to renewed interest in bioconversion of methane.

Whereas current catalysts that can selectively activate the 105 kcal mol-1 C-H bond in methane require high temperatures and pressures, methanotrophs perform this chemistry under ambient conditions using methane monooxygenase (MMO) enzymes. The primary MMO in nature, particulate MMO (pMMO), is a three-subunit, integral membrane protein. Despite extensive research and the availability of multiple crystal structures, the active site structure and chemical mechanism of pMMO remain one of the major unsolved problems in bioinorganic chemistry. Current efforts in the laboratory are directed at elucidating the atomic details of the copper active site, understanding the mechanisms of dioxygen activation and methane oxidation, including how substrates, products, electrons, and protons access the active site, and probing the function of pMMO within the larger context of methanotroph physiology.

To learn more about this project:

Ro, S. Y.; Schachner, L. F.; Koo, C. W.; Purohit, R.; Remis, J. P.; Kenney, G. E.; Liauw, B. W.; Thomas P. M.; Patrie, S. M.; Kelleher, N. L.; Rosenzweig, A. C. Native top-down mass spectrometry provides insights into the copper centers of membrane-bound methane monooxygenase. Nat. Commun. 2019, 10, 2675.

Ross, M. O.; MacMillan, F.; Wang, J.; Nisthal, A.; Lawton, T. J.; Olafson, B. D.; Mayo, S. L.; Rosenzweig, A. C.; Hoffman, B. M. Particulate methane monooxygenase contains only monocopper centers. Science 2019, 364, 566-570.

Ro, S. Y.; Ross, M. O.; Deng, Y. W.; Batelu, S.; Lawton, T. J.; Hurley, J. D.; Stemmler, T. L.; Hoffman, B. M.; Rosenzweig, A. C. From micelles to bicelles: effect of the membrane on particulate methane monooxygenase activity. J. Biol. Chem. 2018, 293, 10457-10465.

Biosynthesis and Transport of Methanobactin

Copper acquisition by methanotrophic bacteria

Biosynthesis of Methylosinus trichosporium OB3b Mbn from its precursor peptide MbnA.

Copper acquisition is particularly important for methanotrophs because their primary metabolic enzyme, particulate methane monooxygenase (pMMO), requires copper for activity. Some methanotrophs meet their high requirement for copper by secreting and reinternalizing methanobactin (Mbn), a peptide-derived, copper-chelating natural product. Beyond its role in methanotrophy, Mbn is a potential therapeutic for Wilson disease, a genetic disorder of toxic copper overload.

All Mbns characterized thus far bind Cu(I) with two nitrogen-containing heterocycles and two adjacent thioamide groups. Mbn is biosynthesized by post-translational modification of a precursor peptide called MbnA, and bioinformatics analyses revealed that the mbnA gene is located within an operon that also includes genes encoding machinery for Mbn transport and biosynthesis. Importantly, these operons are found in a range of non-methanotrophic bacteria, including gram-positive pathogens, suggesting the Mbn-like natural products may be widespread in nature. Current efforts in the laboratory are focused on discovering new Mbns and related natural products, characterizing the proteins involved in Mbn export and import, and unraveling the mechanisms of its biosynthesis.

To learn more about this project:

Kenney, G. E.; Dassama, L. M. K.; Pandelia, M.-E.; Gizzi, A. S.; Martinie, R. J.; Gao, P.; DeHart, C. J.; Schachner, L. F.; Skinner, O. S.; Ro, S. Y., Zhu, X.; Sadek, M.; Thomas, P. M.; Almo, S. C.; Bollinger, J. M., Jr.; Krebs, C.; Kelleher, N. L.; Rosenzweig, A. C. The biosynthesis of methanobactin. Science 2018, 359, 1411-1416.

Park, Y. J.; Kenney, G. E.; Schachner, L. F.; Kelleher, N. L.; Rosenzweig, A. C. Repurposed HisC aminotransferases complete the biosynthesis of some methanobactins. Biochemistry 2018, 57, 3515-3523.

Kenney, G. E.; Rosenzweig, A. C. Methanobactins: maintaining copper homeostasis in methanotrophs and beyond. J. Biol. Chem. 2018, 293, 4606-4615.

Metal Transport

Metal transport

The P1B-ATPase similarity network. Sequences are represented as nodes (colored circles), and the strength of their similarity is indicated by edges (lines connecting colored circles). Sequences are color coded and labeled by their signature TM helix 4 motifs.

Metalloproteins comprise close to one third of all proteins and almost half of all enzymes. Acquisition and management of metal ions is therefore a critical part of metabolism for all forms of life. Metals must be handled such that the correct ions are provided to essential enzymes and proteins, but do not accumulate to deleterious levels. Membrane transporters, metallochaperones, and metal sensors maintain metal ion concentrations in cells and cellular compartments, and aberrant handling of metal ions is linked to numerous human diseases. Understanding metal homeostasis on the molecular level is thus a central problem in cell biology and bioinorganic chemistry.

Current efforts in the laboratory are focused on P1B-ATPases, integral membrane proteins that couple the energy of ATP hydrolysis to translocation of transition metal ions across membranes. One feature unique to the P1B-ATPases is the presence of soluble metal binding domains that are believed to regulate metal transport. Current efforts in the laboratory are directed at determining the metal substrates for previously uncharacterized P1B-ATPases, elucidating the molecular details of metal binding by both the soluble domains and the transmembrane region, and investigating the molecular details of the transport mechanism.

To learn more about this project:

Purohit, R.; Ross, M. O.; Batelu, S.; Kusowski, A.; Stemmler, T. L.; Hoffman, B. M.; Rosenzweig, A. C. A Cu+-specific CopB transporter: revising P1B-type ATPase classification. Proc. Natl. Acad. Sci. USA 2018, 115, 2108-2113.

Smith, A. T.; Ross, M. O.; Hoffman, B. M.; Rosenzweig, A. C. Metal selectivity of a Cd-, Co-, and Zn-transporting P1B-type ATPase. Biochemistry 2016, 56, 85-95.

Smith, A. T.; Barupala, D.; Stemmler, T. L.; Rosenzweig, A. C. A new metal binding domain involved in cadmium, cobalt, and zinc transport. Nat. Chem. Biol. 2015, 11, 678-684.