Marc Creus

Artificial Metalloenzyme for Enantioselective Sulfoxidation Based on Vanadyl-Loaded Streptavidin

Natures catalysts are specifically evolved to carry out efficient and selective reactions. Recent developments in biotechnology have allowed the rapid optimization of existing enzymes for enantioselective processes. However, the ex nihilo creation of catalytic activity from a noncatalytic protein scaffold remains very challenging. Herein, we describe the creation of an artificial enzyme upon incorporation of a vanadyl ion into the biotin-binding pocket of streptavidin, a protein devoid of catalytic activity. The resulting artificial metalloenzyme catalyzes the enantioselective oxidation of prochiral sulfides with good enantioselectivities both for dialkyl and alkyl-aryl substrates (up to 93% enantiomeric excess). Electron paragmagnetic resonance spectroscopy, chemical modification, and mutagenesis studies suggest that the vanadyl ion is located within the biotin-binding pocket and interacts only via second coordination sphere contacts with streptavidin.

Label-Free Detection of Single Protein Molecules and Protein-Protein Interactions Using Synthetic Nanopores

Nanofabricated pores in 20 nm-thick silicon nitride membranes were used to probe various protein analytes as well as to perform an antigen-antibody binding assay. A two-compartment electrochemical cell was separated by a single nanopore, 28 nm in diameter. Adding proteins to one compartment caused current perturbations in the ion current flowing through the pore. These perturbations correlated with both the charge and the size of the protein or of a protein-protein complex. The potential of this nanotechnology for studying protein-protein interactions is highlighted with the sensitive detection of beta-human chorionic gonadotropin, a hormone and clinical biomarker of pregnancy, by monitoring in real time and at a molecular level the formation of a complex between hormones and antibodies in solution. In this form, the assay compared advantageously to immunoassays, with the important difference that labels, immobilization, or amplification steps were no longer needed. In conclusion, we present proof-of-principle that properties of proteins and their interactions can be investigated in solution using synthetic nanopores and that these interactions can be exploited to measure protein concentrations accurately.

X‐Ray Structure and Designed Evolution of an Artificial Transfer Hydrogenase

A structure is worth a thousand words: guided by the crystal structure of an S-selective artificial transfer hydrogenase, designed evolution was used to optimize the selectivity of hybrid catalysts. Fine-tuning of the second coordination sphere of the ruthenium center by introduction of two point mutations allowed the identification of selective artificial transfer hydrogenases for the redn. of dialkyl ketones.

Artificial Metalloenzymes for Asymmetric Allylic Alkylation on the Basis of the Biotin–Avidin Technology

Palladium in the active site: The incorporation of a biotinylated palladium diphosphine within streptavidin yielded an artificial metalloenzyme for the title reaction (see scheme). Chemogenetic optimization of the catalyst by the introduction of a spacer (red star) between biotin (green triangle) and palladium and saturation mutagenesis at position S112X afforded both R- and S-selective artificial asymmetric allylic alkylases.

Hepatic but not brain iron is rapidly chelated by deferasirox in aceruloplasminemia due to a novel gene mutation

Background & Aims Aceruloplasminemia is a rare autosomal recessive neurodegenerative disease associated with brain and liver iron accumulation which typically presents with movement disorders, retinal degeneration, and diabetes mellitus. Ceruloplasmin is a multi-copper ferroxidase that is secreted into plasma and facilitates cellular iron export and iron binding to transferrin. Results A novel homozygous ceruloplasmin gene mutation, c.2554+1G>T, was identified as the cause of aceruloplasminemia in three affected siblings. Two siblings presented with movement disorders and diabetes. Complementary DNA sequencing showed that this mutation causes skipping of exon 14 and deletion of amino acids 809–852 while preserving the open reading frame. Western blotting of liver extracts and sera of affected patients showed retention of the abnormal protein in the liver. Aceruloplasminemia was associated with severe brain and liver iron overload, where hepatic mRNA expression of the iron hormone hepcidin was increased, corresponding to the degree of iron overload. Hepatic iron concentration normalized after 3 and 5 months of iron chelation therapy with deferasirox, which was also associated with reduced insulin demands. During short term treatment there was no clinical or imaging evidence for significant effects on brain iron overload. Conclusions Aceruloplasminemia can show an incomplete clinical penetrance but is invariably associated with iron accumulation in the liver and in the brain. Iron accumulation in aceruloplasminemia is a result of defective cellular iron export, where hepcidin regulation is appropriate for the degree of iron overload. Iron chelation with deferasirox was effective in mobilizing hepatic iron but has no effect on brain iron.

OsO4⋅Streptavidin: A Tunable Hybrid Catalyst for the Enantioselective cis‐Dihydroxylation of Olefins

Enzymatic and homogeneous catalysis have evolved independently to address the challenges in the synthesis of enantiopure products. With the aim of complementing these fields, artificial metalloenzymes, which combine the structural diversity of biocatalysts with the wealth of metal-catalyzed reactions, have attracted increasing attention. [1] In homogeneous catalysis the cis-selective, OsO4-dependent asymmetric dihydroxylation (AD) of olefins ranks among the most powerful methods for the synthesis of vicinal diols. Ligands for homogeneous catalysis have been largely developed by Sharpless and co-workers, and are, with few exceptions, almost exclusively based on quinidine or quinine derivatives. [2] Although most classes of prochiral olefins are dihydroxylated with good activity and selectivity, the cissubstituted olefins are problematic. Nature relies on nonheme iron dioxygenases such as naphthalene dioxygenase (NDO) to perform a related reaction. These enzymes display broad substrate scope. [3] It is believed that both the OsO4- and NDO-catalyzed dihydroxylations proceed by an outer sphere [3+2] mechanism in which the substrate is not bound to the

Activation and inactivation of the iron hormone hepcidin: Biochemical characterization of prohepcidin cleavage and sequential degradation to N-terminally truncated hepcidin isoforms.

The hormone hepcidin is produced mainly in the liver in response to iron loading and inflammation and secreted into the circulation as a 25-amino acid peptide. The 84-amino acid prohormone undergoes limited proteolytic cleavage at a conserved proprotein convertase (PC) recognition site. In addition to the 25-amino acid hepcidin, N-terminally truncated isoforms of lower biological activity are found in plasma and urine. Here we show that a redundant system of proprotein convertases cleaves prohepcidin at the predicted site releasing active hepcidin-25 from the proprotein. In addition to furin mediated cleavage of prohepcidin, we found prohepcidin peptidase activity of proprotein convertases PC5/6, PC7/LPC, PC1/3 and PC2 which was specific for the release of hepcidin-25 from prohepcidin as shown by mass spectrometry. In native tissue extracts, a calcium-dependent prohepcidin peptidase activity is present specifically releasing the 25-mer hepcidin isoform from the recombinant prohormone. In contrast, the 20-mer isoform of hepcidin is generated by a calcium-independent tissue activity which cleaves the 25-mer peptide but has no activity on the entire prohormone. This finding demonstrates the presence of an additional peptidase in this inactivation mechanism for hepcidin. An inhibitor of prohepcidin cleavage was designed and synthesized from d-amino acids (QRRRRR). Biochemical studies indicated that this is a potent and generic inhibitor of prohepcidin cleavage. Biochemical and inhibitor studies of endogenous tissue peptidase activities support the implication of proprotein convertases in the activation of hepcidin. Inactivation of the peptide hormone by N-terminal truncation is mediated by other distinct peptidases, which appear to act sequentially to initial release of hepcidin-25 from the proprotein.

Burkavidin: a novel secreted biotin-binding protein from the human pathogen Burkholderia pseudomallei.

The avidin-biotin technology has many applications, including molecular detection; immobilization; protein purification; construction of supramolecular assemblies and artificial metalloenzymes. Here we present the recombinant expression of novel biotin-binding proteins from bacteria and the purification and characterization of a secreted burkavidin from the human pathogen Burkholderia pseudomallei. Expression of the native burkavidin in Escherichia coli led to periplasmic secretion and formation of a biotin-binding, thermostable, tetrameric protein containing an intra-monomeric disulphide bond. Burkavidin showed one main species as measured by isoelectric focusing, with lower isoelectric point (pI) than streptavidin. To exemplify the potential use of burkavidin in biotechnology, an artificial metalloenzyme was generated using this novel protein-scaffold and shown to exhibit enantioselectivity in a rhodium-catalysed hydrogenation reaction.

Zinc-selective inhibition of the promiscuous bacterial amide-hydrolase DapE: implications of metal heterogeneity for evolution and antibiotic drug design.

The development of resistance to virtually all current antibiotics makes the discovery of new antimicrobial compounds with novel protein targets an urgent challenge. The dapE-encoded N-succinyl-L,L-diaminopimelic acid desuccinylase (DapE) is an essential metallo-enzyme for growth and proliferation in many bacteria, acting in the desuccinylation of N-succinyl-L,L-diaminopimelic acid (SDAP) in a late stage of the anabolic pathway towards both lysine and a crucial building block of the peptidoglycan cell wall. L-Captopril, which has been shown to exhibit very promising inhibitory activity in vitro against DapE and has attractive drug-like properties, nevertheless does not target DapE in bacteria effectively. Here we show that L-captopril targets only the Zn(2+)-metallo-isoform of the enzyme, whereas the Mn(2+)-enzyme, which is also a physiologically relevant isoform in bacteria, is not inhibited. Our finding provides a rationale for the failure of this promising lead-compound to exhibit any significant antibiotic activity in bacteria and underlines the importance of addressing metallo-isoform heterogeneity in future drug design. Moreover, to our knowledge, this is the first example of metallo-isoform heterogeneity in vivo that provides an evolutionary advantage to bacteria upon drug-challenge.

Chemo-Genetic Optimization of DNA Recognition by Metallodrugs using a Presenter-Protein Strategy

The mode of action of precious metal anticancer metallodrugs is generally believed to involve DNA as a target. However, the poor specificity of such drugs often requires high doses and leads to undesirable side-effects. With the aim of improving the specificity of a ruthenium piano-stool complex towards DNA, we employed a presenter protein strategy based on the biotin-avidin technology. Guided by the X-ray structure of the assembly of streptavidin and a biotinylated piano-stool, we explored the formation of metallodrug-mediated ternary complexes with the presenter protein and DNA. The assemblies bound more strongly to telomere G-quadruplexes than to double-stranded DNA; chemo-genetic modifications (varying the complex or mutating the protein) modulated binding to these targets. We suggest that rational targeting of small molecules by presenter proteins could be exploited to bind metallodrugs to preferred macromolecular targets.