Overproduction of Native and Click-able Colanic Acid Slime from Engineered Escherichia coli.

The fundamental biology and application of bacterial exopolysaccharides is gaining increasing attention. However, current synthetic biology efforts to produce the major component of Escherichia sp. slime, colanic acid, and functional derivatives thereof have been limited. Herein, we report the overproduction of colanic acid (up to 1.32 g/L) from d-glucose in an engineered strain of Escherichia coli JM109. Furthermore, we report that chemically synthesized l-fucose analogues containing an azide motif can be metabolically incorporated into the slime layer via a heterologous fucose salvage pathway from Bacteroides sp. and used in a click reaction to attach an organic cargo to the cell surface. This molecular-engineered biopolymer has potential as a new tool for use in chemical, biological, and materials research.

Macrocylases as synthetic tools for ligand synthesis: enzymatic synthesis of cyclic peptides containing metal-binding amino acids.

Improving the sustainability of synthesis is a major goal in green chemistry, which has been greatly aided by the development of asymmetric transition metal catalysis. Recent advances in asymmetric catalysis show that the ability to control the coordination sphere of substrates can lead to improvements in enantioselectivity and activity, in a manner resembling the operation of enzymes. Peptides can be used to mimic enzyme structures and their secondary interactions and they are easily accessible through solid-phase peptide synthesis. Despite this, cyclic peptides remain underexplored as chiral ligands for catalysis due to synthetic complications upon macrocyclization. Here, we show that the solid-phase synthesis of peptides containing metal-binding amino acids, bipyridylalanine (1), phenyl pyridylalanine (2) and N,N-dimethylhistidine (3) can be combined with peptide macrocylization using peptide cyclase 1 (PCY1) to yield cyclic peptides under mild conditions. High conversions of the linear peptides were observed (approx. 90%) and the Cu-bound cyclo(FSAS(1)SSKP) was shown to be a competent catalyst in the Friedel-Crafts/conjugate addition of indole. This study shows that PCY1 can tolerate peptides containing amino acids with classic inorganic and organometallic ligands as side chains, opening the door to the streamlined and efficient development of cyclic peptides as metal ligands.

Halomethyl-Triazoles for Rapid, Site-Selective Protein Modification.

Post-translational modifications (PTMs) are used by organisms to control protein structure and function after protein translation, but their study is complicated and their roles are not often well understood as PTMs are difficult to introduce onto proteins selectively. Designing reagents that are both good mimics of PTMs, but also only modify select amino acid residues in proteins is challenging. Frequently, both a chemical warhead and linker are used, creating a product that is a misrepresentation of the natural modification. We have previously shown that biotin-chloromethyl-triazole is an effective reagent for cysteine modification to give S-Lys derivatives where the triazole is a good mimic of natural lysine acylation. Here, we demonstrate both how the reactivity of the alkylating reagents can be increased and how the range of triazole PTM mimics can be expanded. These new iodomethyl-triazole reagents are able to modify a cysteine residue on a histone protein with excellent selectivity in 30 min to give PTM mimics of acylated lysine side-chains. Studies on the more complicated, folded protein SCP-2L showed promising reactivity, but also suggested the halomethyl-triazoles are potent alkylators of methionine residues.

Palladium in biological media: Can the synthetic chemist's most versatile transition metal become a powerful biological tool?

Palladium catalysed reactions are ubiquitous in synthetic organic chemistry in both organic solvents and aqueous buffers. The broad reactivity of palladium catalysis has drawn interest as a means to conduct orthogonal transformations in biological settings. Successful examples have been shown for protein modification, in vivo drug decaging and as palladium-protein biohybrid catalysts for selective catalysis. Biological media represents a challenging environment for palladium chemistry due to the presence of a multitude of chelators, catalyst poisons and a requirement for milder reaction conditions e.g. lower temperatures. This review looks to identify successful examples of palladium-catalysed reactions in the presence of proteins or cells and analyse solutions to help to overcome the challenges of working in biological systems.

Transition Metal-Free Reduction of Activated Alkenes Using a Living Microorganism.

Microorganisms can be programmed to perform chemical synthesis via metabolic engineering. However, despite an increasing interest in the use of de novo metabolic pathways and designer whole-cells for small molecule synthesis, the inherent synthetic capabilities of native microorganisms remain underexplored. Herein, we report the use of unmodified E. coli BL21(DE3) cells for the reduction of keto-acrylic compounds and apply this whole-cell biotransformation to the synthesis of aminolevulinic acid from a lignin-derived feedstock. The reduction reaction is rapid, chemo-, and enantioselective, occurs under mild conditions (37 °C, aqueous media), and requires no toxic transition metals or external reductants. This study demonstrates the remarkable promiscuity of central metabolism in bacterial cells and how these processes can be leveraged for synthetic chemistry without the need for genetic manipulation.

Chloromethyl-triazole: a new motif for site-selective pseudo-acylation of proteins.

Rapid, site-selective modification of cysteine residues with chloromethyl-triazole derivatives generates pseudo-acyl sLys motifs, mimicking important post-translational modifications. Near-native biotinylation of peptide and protein substrates is shown to be site-selective and modified histone H4 retains functional activity.

Self-Assembly of Disorazole†C1 through a One-Pot Alkyne Metathesis Homodimerization Strategy.

Alkyne metathesis is increasingly explored as a reliable method to close macrocyclic rings, but there are no prior examples of an alkyne-metathesis-based homodimerization approach to natural products. In this approach to the cytotoxic C2-symmetric marine-derived bis(lactone) disorazole C1, a highly convergent, modular strategy is employed featuring cyclization through an ambitious one-pot alkyne cross-metathesis/ring-closing metathesis self-assembly process.

Self-Assembly of Disorazole†C1 through a One-Pot Alkyne Metathesis Homodimerization Strategy.

Alkyne metathesis is increasingly explored as a reliable method to close macrocyclic rings, but there are no prior examples of an alkyne-metathesis-based homodimerization approach to natural products. In this approach to the cytotoxic C2 -symmetric marine-derived bis(lactone) disorazole C1, a highly convergent, modular strategy is employed featuring cyclization through an ambitious one-pot alkyne cross-metathesis/ring-closing metathesis self-assembly process.