Structural and mechanistic basis for RiPP epimerization by a radical SAM enzyme.

D-Amino acid residues, found in countless peptides and natural products including ribosomally synthesized and post-translationally modified peptides (RiPPs), are critical for the bioactivity of several antibiotics and toxins. Recently, radical S-adenosyl-L-methionine (SAM) enzymes have emerged as the only biocatalysts capable of installing direct and irreversible epimerization in RiPPs. However, the mechanism underpinning this biochemical process is ill-understood and the structural basis for this post-translational modification remains unknown.

Exploring the Biosynthetic Potential of TsrM, a B -dependent Radical SAM Methyltransferase Catalyzing Non-radical Reactions.

B -dependent radical SAM enzymes are an emerging enzyme family with approximately 200,000 proteins. These enzymes have been shown to catalyze chemically challenging reactions such as methyl transfer to sp2- and sp3-hybridized carbon atoms. However, to date we have little information regarding their complex mechanisms and their biosynthetic potential.

Crystallographic snapshots of a B-dependent radical SAM methyltransferase.

By catalysing the microbial formation of methane, methyl-coenzyme M reductase has a central role in the global levels of this greenhouse gas. The activity of methyl-coenzyme M reductase is profoundly affected by several unique post-translational modifications, such as  a unique C-methylation reaction catalysed by methanogenesis marker protein 10 (Mmp10), a radical S-adenosyl-L-methionine (SAM) enzyme. Here we report the spectroscopic investigation and atomic resolution structure of Mmp10 from Methanosarcina acetivorans, a unique B (cobalamin)-dependent radical SAM enzyme.

Biosynthesis of the sactipeptide Ruminococcin C by the human microbiome: Mechanistic insights into thioether bond formation by radical SAM enzymes.

Despite its major importance in human health, the metabolic potential of the human gut microbiota is still poorly understood. We have recently shown that biosynthesis of Ruminococcin C (RumC), a novel ribosomally synthesized and posttranslationally modified peptide (RiPP) produced by the commensal bacterium , requires two radical SAM enzymes (RumMC1 and RumMC2) catalyzing the formation of four C-thioether bridges. These bridges, which are essential for RumC's antibiotic properties against human pathogens such as , define two hairpin domains giving this sactipeptide (sulfur-to-α-carbon thioether-containing peptide) an unusual architecture among natural products.

Ruminococcin C, an anti-clostridial sactipeptide produced by a prominent member of the human microbiota .

The human microbiota plays a central role in human physiology. This complex ecosystem is a promising but untapped source of bioactive compounds and antibiotics that are critical for its homeostasis. However, we still have a very limited knowledge of its metabolic and biosynthetic capabilities.

Screening of a Drug Library Identifies Inhibitors of Cell Intoxication by CNF1.

Cytotoxic necrotizing factor 1 (CNF1) is a toxin produced by pathogenic strains of Escherichia coli responsible for extra-intestinal infections. CNF1 deamidates Rac1, thereby triggering its permanent activation and worsening inflammatory reactions. Activated Rac1 is prone to proteasomal degradation.

Parallel evolution of non-homologous isofunctional enzymes in methionine biosynthesis.

Experimental validation of enzyme function is crucial for genome interpretation, but it remains challenging because it cannot be scaled up to accommodate the constant accumulation of genome sequences. We tackled this issue for the MetA and MetX enzyme families, phylogenetically unrelated families of acyl-L-homoserine transferases involved in L-methionine biosynthesis. Members of these families are prone to incorrect annotation because MetX and MetA enzymes are assumed to always use acetyl-CoA and succinyl-CoA, respectively.

Dynamical properties of α-synuclein in soluble and fibrillar forms by Quasi Elastic Neutron Scattering.

In the present paper, Quasi Elastic Neutron Scattering (QENS) results, gathered at different energy resolution values at the ISIS Facility (RAL, UK), on α-synuclein in soluble and fibrillar forms as a function of temperature and exchanged wave-vector Q are shown. The measurements reveal a different dynamic behavior of the soluble and fibrillar forms of α-synuclein as a function of thermal stress. In more detail, the dynamics of each protein form reflects its own complex conformational heterogeneity.