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Access to new non‐canonical amino acid residues is crucial for medicinal chemistry and chemical biology. Analogues of the amino acid methionine have been far less explored—despite their use in biochemistry, pharmacology and peptide bioconjugation. This is largely due to limited synthetic access. Herein, we exploit a new disconnection to access non‐natural methionines through the development of a photochemical method for the radical α‐C−H functionalization of sulfides with alkenes, in water, using inexpensive and commercially‐available riboflavin (vitamin B2) as a photocatalyst. Our photochemical conditions allow the two‐step synthesis of novel methionine analogues—by radical addition to unsaturated amino acid derivatives—and the chemoselective modification of peptide side‐chains to yield non‐natural methionine residues within small peptides. The mechanism of the bio‐inspired flavin photocatalysis has been probed by experimental, DFT and TDDFT studies. [ABSTRACT FROM AUTHOR]

Inhibition of kynurenine 3-monooxygenase (KMO), an enzyme in the eukaryotic tryptophan catabolic pathway (that is, kynurenine pathway), leads to amelioration of Huntington's-disease-relevant phenotypes in yeast, fruitfly and mouse models (1-5), [...]

Post-translational modification of proteins by poly(ADP-ribosyl) ation regulates many cellular pathways that are critical for genome stability, including DNA repair, chromatin structure, mitosis and apoptosis (1). Poly(ADP-ribose) (PAR) is composed of repeating ADP-ribose units linked via a unique glycosidic ribose-ribose bond, and is synthesized from NAD by PAR polymerases (1,2). PAR glycohydrolase (PARG) is the only protein capable of specific hydrolysis of the ribose-ribose bonds present in PAR chains; its deficiency leads to cell death (3,4). Here we show that filamentous fungi and a number of bacteria possess a divergent form of PARG that has all the main characteristics of the human PARG enzyme. We present the first PARG crystal structure (derived from the bacterium Thermomonospora curvata), which reveals that the PARG catalytic domain is a distant member of the ubiquitous ADP-ribose-binding macrodomain family (5,6). High-resolution structures of T. curvata PARG in complexes with ADP-ribose and the PARG inhibitor ADP-HPD, complemented by biochemical studies, allow us to propose a model for PAR binding and catalysis by PARG. The insights into the PARG structure and catalytic mechanism should greatly improve our understanding of how PARG activity controls reversible protein poly(ADP-ribosyl) ation and potentially of how the defects in this regulation are linked to human disease., Whereas the mechanism and functional aspects of PAR synthesis have been extensively characterized, the present understanding of the PAR-degradation pathways catalysed by PARG is comparatively poor. Until now, the catalytic [...]

The structure-function studies on the protein were carried out and its interaction with sphaeroides heme protein (SHP) was examined to gain further insight into the properties and role of diheme cytochrome c (DHC). Evidence of complementary binding, favorable midpoint potentials, and effect electron transfer in the DHC-SHP system is provided.

A detailed structural, spectroscopic and thermodynamic characterization of cytochrome P450 BioI is conducted and reported. Results demonstrate unexpected flexibility of the active site with the capacity to bind tightly to certain steroids and to bulky azole drugs, as well as long-chain fatty acids. The result also reveals that BioI is purified from Escherichia coli with palmitic acid bound, which explains its isolation in a mixed spin state.

The use of CO2 as a chemical building block is of considerable interest. To achieve carbon fixation at ambient conditions, (de)carboxylase enzymes offer an attractive route but frequently require elevated [CO2] levels to yield the acid product. However, it has recently been shown that the coupling of a UbiD-type decarboxylase with carboxylic acid reductase yields the corresponding aldehyde product at near ambient [CO2]. Here, we show this approach can be expanded to different UbiD and CAR enzymes to yield alternative products, in this case, the production of pyrrole-2-carbaldehyde from pyrrole, using Pseudomonas aeruginosa HudA/PA0254 in combination with Segniliparus rotundus CAR. This confirms the varied substrate range of the respective UbiD and CAR enzymes can be harnessed in distinct combinations to support production of a wide range of aldehydes via enzymatic CO2 fixation. [ABSTRACT FROM AUTHOR]

Research has been conducted on the single- and double mutant flavocytochromes c (sub)3. The structure of the one of these enzymes indicate the existence of a water molecule at the enzyme's active site.

Results point out that His505 of the Shewanella frigidimarina fumarate reductase is not required for sodium ion binding. However, it may be involved in the pK(sub)a modulation/protonation of a key active site substrate-binding residue, His504, thereby influencing the catalytic activity of the enzyme.

Flavocytochrome P450 BM3 is a bacterial P450 system in which a fatty acid hydroxylase P450 is fused to a mammalian-like diflavin NADPH-P450 reductase in a single polypeptide. The enzyme is soluble (unlike mammalian P450 redox systems) and its fusion arrangement affords it the highest catalytic activity of any P450 mono-oxygenase. This article discusses the fundamental properties of P450 BM3 and how progress with this model P450 has affected our comprehension of P450 systems in general.

The crystal structure of the diheme cytochrome NapB from Haemophilus influenzae shows an unusual fold with two heme groups exhibiting nearly parallel heme planes and iron-to iron distance of only 9.9 angstroms. Data indicate that the structural organization of the heme groups resemble that of split-Soret diheme cytochrome c but folded differently.

Research has been conducted on the fumarate. The mechanism for the fumarate reduction in the respiratory fumarate reductases has been investigated and the results indicate that the X-ray substrate-bound structure forms of these enzymes are well positioned.

Dynamical changes in protein structures are essential for protein function and occur over femtoseconds to seconds timescales. X‐ray free electron lasers have facilitated investigations of structural dynamics in proteins with unprecedented temporal and spatial resolution. Light‐activated proteins are attractive targets for time‐resolved structural studies, as the reaction chemistry and associated protein structural changes can be triggered by short laser pulses. Proteins with different light‐absorbing centres have evolved to detect light and harness photon energy to bring about downstream chemical and biological output responses. Following light absorption, rapid chemical/small‐scale structural changes are typically localised around the chromophore. These localised changes are followed by larger structural changes propagated throughout the photoreceptor/photocatalyst that enables the desired chemical and/or biological output response. Time‐resolved serial femtosecond crystallography (SFX) and solution scattering techniques enable direct visualisation of early chemical change in light‐activated proteins on timescales previously inaccessible, whereas scattering gives access to slower timescales associated with more global structural change. Here, we review how advances in time‐resolved SFX and solution scattering techniques have uncovered mechanisms of photochemistry and its coupling to output responses. We also provide a prospective on how these time‐resolved structural approaches might impact on other photoreceptors/photoenzymes that have not yet been studied by these methods. [ABSTRACT FROM AUTHOR]

Author(s): Mary Ortmayer [1]; Pierre Lafite [1]; Binuraj R. K. Menon [1]; Tewes Tralau [1]; Karl Fisher [1]; Lukas Denkhaus [1]; Nigel S. Scrutton [1]; Stephen E. J. Rigby [1]; [...]

The complete amino acid sequence of the low-redox potential cytochrome c-551.5 from Rhodobacter sphaeroides was obtained through automated Edman degradation and mass spectroscopy. It is composed of 139 residues and two typical Cys-X-X-Cys-His heme binding sites. A homologous low-redox potential cytochrome was also sequenced from Rhodobacter adriaticus and was observed to have 126 residues. The Rhodobacter diheme cytochromes are 21-24% similar to the translated open reading frame SLL1886 from Synechocystis sp. PCC6801.

Author(s): Karl A. P. Payne [1]; Mark D. White [1]; Karl Fisher [1]; Basile Khara [1]; Samuel S. Bailey [1]; David Parker [2]; Nicholas J. W. Rattray [1]; Drupad K. [...]