Methanogenesis is an anaerobic respiration that generates methane as the final product of metabolism. In aerobic respiration, organic matter such as glucose is oxidized to CO, and O is reduced to HO. In contrast, during hydrogenotrophic methanogenesis, H is oxidized to H, and CO is reduced to CH. Although similar in principle to other types of respiration, methanogenesis has some distinctive features: the energy yield is very low, ≤1 ATP per methane generated, and only methanogens - organisms capable of this specialized metabolism - carry out biological methane production. Methanogens, like the process they catalyze, are similarly distinctive. Methanogens are comprised exclusively of archaea. They are obligate methane producers, that is, they do not grow using fermentation or alternative electron acceptors for respiration. Finally, methanogens are strict anaerobes and do not grow in the presence of O. Historically, methanogenesis has been viewed as a highly specialized metabolism restricted to a narrow group of prokaryotes. However, recent developments have revealed enormous diversity within the methanogens and suggest that this metabolism is one of the most ancient on earth.

Strictosidine synthase (STR1) catalyzes a Pictet–Spengler reaction (PSR) forming strictosidine, a likely biosynthetic key to all higher plant monoterpenoid indole alkaloids. Increasing the biocatalytic capacity of the enzyme may make it a powerful tool for generation of compound libraries with enhanced structural diversity and pharmaceutical activity. Herein two production routes of a rare class of azepino­[3,4,5-cd]-indoles are developed: a complementary STR1-dependent chemoenzymatic and stereoselectively chemical route to an epimeric 1H-azepino­[3,4,5-cd]­indolyl strictosidine or vincoside, respectively. Mechanisms of the asymmetric catalysis are proposed based on computational calculations and X-ray analysis of STR1-ligand complexes. Further chemoenzymatic manipulation of the complementary PSR products resulted in several diverse and complex azepino-indole alkaloids, in which two alkaloids with the epimeric center directs the discovered antimalaria activity: 4α­(S) with IC50 ≈ 3.4 μM, 4β­(R) with IC50 ≈ 6.1 μM. The chemoenzymatic synthesis may significantly extend the applications of the enantiospecific STR1-based PSR in the future.

Catalyzing the key step for anaerobic production and/or oxidation of methane and likely other short-chain alkanes, methyl coenzyme M reductase (Mcr) and its homologs play a key role in the global carbon cycle. The McrA subunit possesses up to five conserved posttranslational modifications (PTMs) at its active site. It was previously suggested that methanogenesis marker protein 10 (Mmp10) could play an important role in methanogenesis. To systematically examine its physiological role, mmpX (locus tag MMP1554), the gene encoding Mmp10 in Methanococcus maripaludis, was deleted with a new genetic tool, resulting in the complete loss of the 5-C-(S)-methylarginine PTM of residue 275 in the McrA subunit. When the ΔmmpX mutant was complemented with the wild-type gene expressed by either a strong or a weak promoter, methylation was fully restored. Compared to the parental strain, maximal rates of methane formation by whole cells were reduced by 40 to 60% in the ΔmmpX mutant. The reduction in activity was fully reversed by the complement with the strong promoter. Site-directed mutagenesis of mmpX resulted in a differential loss of arginine methylation among the mutants in vivo, suggesting that activities of Mmp10 directly modulated methylation. R275 was present in a highly conserved PXRR275(A/S)R(G/A) signature sequence in McrAs. The only other protein in M. maripaludis containing a similar sequence was not methylated, suggesting that Mmp10 is specific for McrA. In conclusion, Mmp10 modulates the methyl-Arg PTM on McrA in a highly specific manner, which has a profound impact on Mcr activity. IMPORTANCE Mcr is the key enzyme in methanogenesis and a promising candidate for bioengineering the conversion of methane to liquid fuel. Our knowledge of Mcr is still limited. In terms of complexity, uniqueness, and environmental importance, Mcr is more comparable to photosynthetic reaction centers than conventional enzymes. PTMs have long been hypothesized to play key roles in modulating Mcr activity. Here, we directly link the mmpX gene to the arginine PTM of Mcr, demonstrate its association with methanogenesis activity, and offer insights into its substrate specificity and putative cofactor binding sites. This is also the first time that a PTM of McrA has been shown to have a substantial impact on both methanogenesis and growth in the absence of additional stressors.

A Cu(II)-catalyzed ortho-selective functionalization of free phenols with trifluoroborates to afford C-C coupling products under mild conditions has been developed. A variety of functional groups on the phenol and the potassium aminomethyltrifluoroborate substrates were found compatible, furnishing the corresponding products in moderate to excellent yields. A single-electron transfer radical coupling mechanism involving a six-membered transition state is proposed to rationalize the high levels of ortho-selectivity in the reaction. This protocol provides straightforward access to ortho-aminomethyl-substituted phenols, unnatural amino acids and other bioactive small molecules.