Noncanonical Heme Ligands Steer Carbene Transfer Reactivity in an Artificial Metalloprotein

<a>Changing the primary metal coordination sphere is a powerful strategy for modulating metalloprotein properties. Taking advantage of this approach, we have replaced the proximal histidine ligand in myoglobin with the histidine analogues N_d-methylhistidine (NMH), 5‑thiazoylalanine (5ThzA), 4-thiazoylalanine (4ThzA) and 3-(3-thienyl)alanine (3ThiA) by amber stop codon suppression using engineered pyrrolysyl-tRNA synthetases, including two newly evolved enzymes. In addition to tuning the heme redox potential over a >200 mV range, these noncanonical ligands modulate the protein’s promiscuous carbene transfer activity with ethyl diazoacetate. Myoglobin variants with increased reduction potentials (NMH and 5ThzA) proved superior for cyclopropanation and N-H insertion, especially under aerobic conditions, and could even promote these reactions in the absence of reducing agent. In contrast, the variants with the lowest <i>E</i>^o values (4ThzA and 3ThiA) exhibit comparatively high S-H insertion activity even though the respective histidine surrogates do not coordinate the heme iron. Given the important functional roles played by histidine in many enzymes, these genetically encoded histidine analogues represent valuable tools for probing mechanism and enabling new chemistries in metalloprotein</a>s.

Noncanonical Heme Ligands Steer Carbene Transfer Reactivity in an Artificial Metalloprotein

<a>Changing the primary metal coordination sphere is a powerful strategy for modulating metalloprotein properties. Taking advantage of this approach, we have replaced the proximal histidine ligand in myoglobin with the histidine analogues N_d-methylhistidine (NMH), 5‑thiazoylalanine (5ThzA), 4-thiazoylalanine (4ThzA) and 3-(3-thienyl)alanine (3ThiA) by amber stop codon suppression using engineered pyrrolysyl-tRNA synthetases, including two newly evolved enzymes. In addition to tuning the heme redox potential over a >200 mV range, these noncanonical ligands modulate the protein’s promiscuous carbene transfer activity with ethyl diazoacetate. Myoglobin variants with increased reduction potentials (NMH and 5ThzA) proved superior for cyclopropanation and N-H insertion, especially under aerobic conditions, and could even promote these reactions in the absence of reducing agent. In contrast, the variants with the lowest <i>E</i>^o values (4ThzA and 3ThiA) exhibit comparatively high S-H insertion activity even though the respective histidine surrogates do not coordinate the heme iron. Given the important functional roles played by histidine in many enzymes, these genetically encoded histidine analogues represent valuable tools for probing mechanism and enabling new chemistries in metalloprotein</a>s.

Macrocyclic NHC complexes of group 10 elements with enlarged aromaticity for biological studies

Two sets of macrocyclic, bio-inspired, non-heme ligands are utilized for the synthesis of NiII, PdII and PtII complexes.

Biomimetic Non-Heme Iron-Catalyzed Epoxidation of Challenging Terminal Alkenes Using Aqueous H2O2 as an Environmentally Friendly Oxidant

Catalysis mediated by iron complexes is emerging as an eco-friendly and inexpensive option in comparison to traditional metal catalysis. The epoxidation of alkenes constitutes an attractive application of iron(III) catalysis, in which terminal olefins are challenging substrates. Herein, we describe our study on the design of biomimetic non-heme ligands for the in situ generation of iron(III) complexes and their evaluation as potential catalysts in epoxidation of terminal olefins. Since it is well-known that active sites of oxidases might involve imidazole fragment of histidine, various simple imidazole derivatives (seven compounds) were initially evaluated in order to find the best reaction conditions and to develop, subsequently, more elaborated amino acid-derived peptide-like chiral ligands (10 derivatives) for enantioselective epoxidations.

A heme-binding domain controls regulation of ATP-dependent potassium channels

Heme iron has many and varied roles in biology. Most commonly it binds as a prosthetic group to proteins, and it has been widely supposed and amply demonstrated that subtle variations in the protein structure around the heme, including the heme ligands, are used to control the reactivity of the metal ion. However, the role of heme in biology now appears to also include a regulatory responsibility in the cell; this includes regulation of ion channel function. In this work, we show that cardiac KATP channels are regulated by heme. We identify a cytoplasmic heme-binding CXXHX16H motif on the sulphonylurea receptor subunit of the channel, and mutagenesis together with quantitative and spectroscopic analyses of heme-binding and single channel experiments identified Cys628 and His648 as important for heme binding. We discuss the wider implications of these findings and we use the information to present hypotheses for mechanisms of heme-dependent regulation across other ion channels.