MbnC is not required for the formation of the N-terminal oxazolone in the methanobactin from <em>Methylosinus trichosporium</em> OB3b.

Methanobactins (MBs) are ribosomally synthesized and post-translationally modified peptides (RiPPs) produced by methanotrophs for copper uptake. The post-translational modification that define MBs is the formation of two heterocyclic groups with associated thioamines from X-Cys dipeptide sequences. Both heterocyclic groups in the MB from Methylosinus trichosporium OB3b (MB-OB3b) are oxazolone groups. The precursor gene for MB-OB3b, mbnA, which is part of a gene cluster that contains both annotated and unannotated genes. One of those unannotated genes, mbnC, is found in all MB operons, and in conjunction with mbnB, is reported to be involved in the formation of both heterocyclic groups in all MBs. To determine the function of mbnC, a deletion mutation was constructed in M. trichosporium OB3b, and the MB produced from the ΔmbnC mutant was purified and structurally characterized by UV-visible absorption spectroscopy, mass spectrometry and solution NMR spectroscopy. MB-OB3b from ΔmbnC was missing the C-terminal Met and also found to contain a Pro and a Cys in place of the pyrrolidiny-oxazolone-thioamide group. These results demonstrate MbnC is required for the formation of the C-terminal pyrrolidinyl-oxazolone-thioamide group from the Pro-Cys dipeptide, but not for the formation of the N-terminal 3-methylbutanol-oxazolone-thioamide group from the N-terminal dipeptide Leu-Cys. IMPORTANCE A number of environmental and medical applications have been proposed for MBs, including bioremediation of toxic metals, nanoparticle formation, as well as for the treatment of copper- and iron-related diseases. However, before MBs can be modified and optimized for any specific application, the biosynthetic pathway for MB production must be defined. The discovery that mbnC is involved in the formation of the C-terminal oxazolone group with associated thioamide but not for the formation of the N-terminal oxazolone group with associated thioamide in M. trichosporium OB3b suggests the enzymes responsible for post-translational modification(s) of the two oxazolone groups are not identical

Oxygen generation via water splitting by a novel biogenic metal ion binding compound.

Methanobactins (MBs) are small (&lt;1,300 Da) post-translationally modified copper-binding peptides and represent the extracellular component of a copper acquisition system in some methanotrophs. Interestingly, MBs can bind a range of metal ions, with some reduced after binding, e.g., Cu2+ reduced to Cu+ Other metal ions, however, are bound but not reduced, e.g., K+ The source of electrons for selective metal ion reduction has been speculated to be water but never empirically shown. Here, using H218O, we show that when MB from Methylocystis sp strain SB2 (MB-SB2) and Methylosinus trichosporium OB3b (MB-OB3) were incubated in the presence of either Au3+, Cu2, and Ag+, 18,18O2 and free protons were released. No 18,18O2 production was observed either in presence of MB-SB2 or MB-OB3b alone, gold alone, copper alone, silver alone or when K+ or Mo2+ was incubated with MB-SB2.In contrast to MB-OB3b, MB-SB2 binds Fe3+ with an N2S2 coordination and will also reduce Fe3+ to Fe2+ Iron reduction was also found to be coupled to oxidation of 2H2O and generation of O2 MB-SB2 will also couple Hg2+, Ni2+ and Co2+ reduction to the oxidation of 2H2O and generation of O2, but MB-OB3b will not, ostensibly as MB-OB3b binds but does not reduce these metal ions.To determine if the O2 generated during metal ion reduction by MB could be coupled to methane oxidation, 13CH4 oxidation by Methylosinus trichosporium OB3b was monitored under anoxic conditions. The results demonstrate O2 generation from metal ion reduction by MB-OB3b can support methane oxidation.IMPORTANCEThe discovery that MB will couple the oxidation of H2O to metal ion reduction and the release of O2 suggests that methanotrophs expressing MB may be able to maintain their activity in hypoxic/anoxic conditions through "self-generation" of dioxygen required for the initial oxidation of methane to methanol. Such an ability may be an important factor in enabling methanotrophs to not only colonize the oxic-anoxic interface where methane concentrations are highest, but also tolerate significant temporal fluctuations of this interface. Given that genomic surveys often show evidence of aerobic methanotrophs within anoxic zones, the ability to express MB (and thereby generate dioxygen) may be an important parameter in facilitating their ability to remove methane, a potent greenhouse gas, before it enters the atmosphere

Role of vitamin B12 on methylmalonyl-CoA mutase activity*

Vitamin B12 is an organometallic compound with important metabolic derivatives that act as cofactors of certain enzymes, which have been grouped into three subfamilies depending on their cofactors. Among them, methylmalonyl-CoA mutase (MCM) has been extensively studied. This enzyme catalyzes the reversible isomerization of L-methylmalonyl-CoA to succinyl-CoA using adenosylcobalamin (AdoCbl) as a cofactor participating in the generation of radicals that allow isomerization of the substrate. The crystal structure of MCM determined in Propionibacterium freudenreichii var. shermanii has helped to elucidate the role of this cofactor AdoCbl in the reaction to specify the mechanism by which radicals are generated from the coenzyme and to clarify the interactions between the enzyme, coenzyme, and substrate. The existence of human methylmalonic acidemia (MMA) due to the presence of mutations in MCM shows the importance of its role in metabolism. The recent crystallization of the human MCM has shown that despite being similar to the bacterial protein, there are significant differences in the structural organization of the two proteins. Recent studies have identified the involvement of an accessory protein called MMAA, which interacts with MCM to prevent MCM’s inactivation or acts as a chaperone to promote regeneration of inactivated enzyme. The interdisciplinary studies using this protein as a model in different organisms have helped to elucidate the mechanism of action of this isomerase, the impact of mutations at a functional level and their repercussion in the development and progression of MMA in humans. It is still necessary to study the mechanisms involved in more detail using new methods