Methanobactin

Methanobactin (mb) is a class of copper-binding chromopeptides initially identified in the methanotroph Methylococcus capsulatus Bath - and later in Methylosinus Tricasporium OB3b - during the isolation of the membrane-associated or particulate methane monooxygenase (pMMO).^[1] It is thought to be secreted to the extracellular media to recruit copper, a critical component of methane monooxygenase, the first enzyme in the series that catalyzes the oxidation of methane into methanol. Methanobactin functions as a chalkophore, similar to iron siderophores, by binding to Cu(II) or Cu(I) then shuttling the copper into the cell. Additionally, methanobactin can reduce Cu(II), which is toxic to cells, to Cu(I), the form used in pMMO.^[2]

Strains of Methanobactin

OB3b

OB3b is a commonly studied methanobactin. It has a molecular weight of 1154 Da when metal free. OB3b is composed of 9 amino acid residues with two oxazalone rings, which take part in binding to copper ions.^{[3] [4]} The oxazalone rings are susceptible to cleavage under low pH conditions, which releases any metal ion bound to the rings.

SB2

SB2 is produced by Methylocystis bacteria. SB2 is much smaller than OB3b with a molecular weight of 851Da when metal free.^[5] SB2 contains one imidazole ring and one oxazalone ring as well as a sulfate group that are thought to partake in binding copper.

References

1. ^ Dong W. Choi, et al. "Spectral, Kinetic, and Thermodynamic Properties of Cu(I) and Cu(II) Binding by Methanobactin from M. trichosporium OB3b." Biochemistry 2006, 45 (5), 1442-1453
2. ^ Amanda S. Hakemian, et al. "The Copper Chelator Methanobactin from Methylosinus trichosporium OB3b Binds Copper(I)" Journal of the American Chemical Society 2005, 127 (49), 17142-17143
3. ^ Hyung J. Kim, et al. "Methanobactin, a Copper-Acquisition Compound from Methane-Oxidizing Bacteria." Science 10 September 2004: Vol. 305 no. 5690 pp. 1612-1615
4. ^ Lee A. Behling, et al. "NMR, Mass Spectrometry and Chemical Evidence Reveal a Different Chemical Structure for Methanobactin That Contains Oxazolone Rings." Journal of the American Chemical Society 2008, 130 (38), 12604-12605
5. ^ Benjamin D. Krentz, et al. "A Comparison of Methanobactins from M. trichosporium OB3b and Methylocystis Strain SB2 Predicts Methanobactins Are Synthesized from Diverse Peptide Precursors Modified To Create a Common Core for Binding and Reducing Copper Ions" Biochemistry 2010, 49 (47), 10117-10130