Journal of Biological Inorganic Chemistry最新文献

Bacteria and fungi produce natural products that coordinate copper for a variety of functions. Many copper-binding natural products function as copper-chelating metallophores, or chalkophores, that scavenge copper from the environment to meet cellular needs. By contrast, some compounds sequester toxic levels of environmental copper to protect the producing microorganism. These copper-binding compounds often have antimicrobial activities as well. In recent years, a number of new copper-coordinating natural products have been reported, including both ribosomally and non-ribosomally synthesized molecules. There have also been significant advances in understanding the biosynthesis of these and previously known copper chelators, leading to the discovery of new enzyme families. This review summarizes the recently discovered copper-binding natural products, their biosynthetic pathways, and their functions. By highlighting key biosynthetic enzymes, we hope to inspire the discovery of new copper-coordinating natural products that may be used as therapeutics and antimicrobial agents.

PnpC1C2 is an enzyme from the soil bacterium Pseudomonas putida DLL-E4 that is in the pathway for the oxidative catabolism of 4-nitrophenol. PnpC1C2 oxidatively cleaves hydroquinone into γ-hydroxymuconic semialdehyde. It belongs to the type II hydroquinone dioxygenase family, a relatively uncharacterized group of mononuclear non-heme Fe(II)-dependent enzymes that catalyze oxidative ring-cleavage reactions, which includes the well-studied catechol extradiol dioxygenases as well as the structurally unrelated 2,6-dichlorohydroquinone dioxygenase (PcpA). Steady-state kinetics studies using UV/Vis spectroscopy were performed to characterize the enzyme specificity towards various substituted hydroquinones. In addition to its native substrate, PnpC1C2 was active towards a variety of monosubstituted hydroquinones. Methyl- and methoxyhydroquinone showed a moderately higher $K_{\mathrm{mA}}^{\mathrm{app}}$ , and chloro- and bromohydroquinone showed a moderately lower $k_{\mathrm{cat}}^{\mathrm{app}}$ , but all had a $k_{\mathrm{cat}}^{\mathrm{app}}\left(\phantom{k_{\mathrm{cat}}^{\mathrm{app}}{K}_{\mathrm{mA}}^{\mathrm{app}}}\right)K_{\mathrm{mA}}^{\mathrm{app}}$ within an order of magnitude of unsubstituted hydroquinone. Likewise, only small differences in the rates of mechanism-based inactivation were observed among these substrates. Among disubstituted hydroquinones, only 2,6- and 2,5-dimethylhydroquinone showed any activity, with the latter only barely detectable. A variety of para-substituted phenols were found to be good inhibitors of PnpC1C2. NMR studies were performed to determine the regioselectivity of ring-cleavage with monosubstituted hydroquinones. All monosubstituted hydroquinones tested (methyl-, chloro-, bromo-, and methoxyhydroquinone) yielded exclusively the 1,6-cleavage product. Thus, PnpC1C2 shows notable differences in both its substrate specificity and the ring-cleavage regioselectivity compared to that of PcpA. These results provide an important basis for future comparison of structure-function correlations among the hydroquinone ring-cleaving dioxygenases.

In the reaction of aquacobalamin (aquaCbl) with chlorite, a stable species is detected and assigned as a Co(III)-chlorite complex, Co(III)-OClO^-. Its UV-Vis spectrum is almost identical to that of aquaCbl, except for some minor differences at ~ 430 nm; cyanide can eliminate and prevent these changes. The ¹H-NMR spectra reveal strong influences of chlorite on the B2 and B4 protons of the cobalt-bound dimethyl benzimidazole ligand. Together, the UV-Vis and NMR titrations suggest a Kd of 10 mM or higher for chlorite on Cbl. Resonance Raman spectra reveal minor changes in the spectrum of aquaCbl to chlorite-as well as a disappearance of the free chlorite signals, consistent with Cbl-chlorite complex formation. Corroboration for these interpretations is also offered from mass spectrometry and DFT calculations. This Co(III)-OClO^- complex would be a stable analogue of the first reaction intermediate in the catalytic cycle of chlorite dismutase, or in the reaction of chlorite with a number of other heme proteins. The differences in reactivity between Co(III) cobalamin and Fe(III) heme towards chlorite are analyzed and rationalized, leading to a reconciliation of experimental and computational data for the latter.

The aim of this study was to elucidate the potential mechanism of the antihyperglycemic action of the donut-shaped Preyssler-Pope-Jeannin polyanion salt (NH₄)₁₄[NaP₅W₃₀O₁₁₀] 31H₂O (NaP₅W₃₀) and its effect on metabolic disorders associated with diabetes. For this purpose, relevant parameters of blood glucose regulation, lipid profile, and electrolyte status were monitored in streptozotocin (STZ)-induced diabetic rats that were orally treated with 20 mg/kg/day NaP₅W₃₀ for three weeks. The serum insulin concentration was increased in diabetic animals treated with NaP₅W₃₀ (20 mg/kg/day, per os, three weeks), which could be one of the possible mechanisms of the confirmed antihyperglycemic effect. In addition, the administration of NaP₅W₃₀ significantly reduced hyperglycemia and glycated haemoglobin A_1c (HbA_1c) in STZ-induced diabetic rats, although normoglycemic values were not achieved. Furthermore, a statistically significant 1.3-fold reduction in serum total cholesterol and a 1.7-fold reduction in high-density lipoprotein (HDL) cholesterol were observed in the NaP₅W₃₀ treatment group compared to the diabetic control group. In contrast, NaP₅W₃₀ had no effect on homeostasis model assessment of insulin resistance (HOMA-IR) index values, electrolyte concentrations, or serum concentrations of low-density lipoprotein (LDL) cholesterol, apolipoprotein A1 (Apo A1), apolipoprotein B (Apo B), or total triglycerides. In summary, NaP₅W₃₀ effectively improved glycoregulation in diabetic rats via the considerable stimulation of insulin as a putative mechanism. Moreover, NaP₅W₃₀ did not affect rat weight or disrupt lipid and electrolyte status, common diabetes-followed side effects and risk factors for various life-threatening complications. Thus, NaP₅W₃₀ could be considered a promising antidiabetic drug-candidate that deserves further investigation.

NiaR is a regulatory protein that represses the expression of proteins involved in the de novo biosynthesis and uptake of nicotinic acid (NA), with NA acting as a co-repressor. The previously published structure of NiaR from Thermotoga maritima (TmNiaR) identified it as a functional homodimer containing a transition metal ion in a suspected NA-binding pocket. Here, we present the crystal structure of NA bound to the iron-metalated form of TmNiaR. Supported by spectroscopic and solution studies, this structure shows that NA binds to a protein-bound ferrous ion via its ring nitrogen. In addition, the carboxylate group on NA interacts with Tyr108 from the dyad-related subunit, repositioning the likely DNA-binding domains of the dimer to promote high-affinity interactions with DNA operators. The specificity of TmNiaR for NA can be explained by the hydrogen bonding scheme within the NA-binding pocket.

Native metalloenzymes are unparalleled in their ability to perform efficient small molecule activation reactions, converting simple substrates into complex products. Most of these natural systems possess multiple metallocofactors to facilitate electron transfer or cascade catalysis. While the field of artificial metalloenzymes is growing at a rapid rate, examples of artificial enzymes that leverage two distinct cofactors remain scarce. In this work, we describe a new class of artificial enzymes containing two different metallocofactors, incorporated through bioorthogonal strategies. Nickel-substituted rubredoxin (Ni^Rd), which is a structural and functional mimic of [NiFe] hydrogenases, is used as a scaffold. Incorporation of a synthetic bimetallic inorganic complex based on a macrocyclic biquinazoline ligand (M^MBQ) was accomplished using a novel chelating thioether linker. Neither the structure of the Ni^Rd active site nor the M^MBQ were altered upon attachment, and each site retained independent redox activity. Electrocatalysis was observed from each site, with the switchability of the system demonstrated through the use of catalytically inert metal centers. This M^MBQ-Ni^Rd platform offers a new avenue to create multicofactor artificial metalloenzymes in a robust system that can be easily tuned both through modifications to the protein scaffold and the synthetic moiety, with applications for redox catalysis and tandem reactivity.

Iron-sulfur proteins perform a wide variety of reactions central to the metabolisms of all living organisms. Foundational to their reaction chemistry are the rich electronic structures of their constituent Fe-S clusters, which differ in important ways from the active sites of mononuclear Fe enzymes. In this perspective, we summarize the essential electronic structure features that make Fe-S clusters unique, and point to the need for studies aimed at understanding the electronic basis for their reactivity under physiological conditions. Specifically, at ambient temperature, both the ground state and a large number of excited states are thermally populated, and thus a complete understanding of Fe-S cluster reactivity must take into account the properties, energies, and reactivity patterns of these excited states. We highlight prior research toward characterizing the low-energy excited states of Fe-S clusters that has established what is now a consensus model of these excited state manifolds and the bonding interactions that give rise to them. In particular, we discuss the low-energy alternate spin states and valence electron configurations that occur in Fe-S clusters of varying nuclearities, and finally suggest that there may be unrecognized functional roles for these states.

Related to the inactive form of nitrile hydratase, NHase, that contains Fe(NO) within tripeptide N₂S₂ binding environment, the NO transfer reactivity of (bis-mercaptoethane diazacycloheptane)Fe(NO) and (bis-mercaptoethane diazadimethylethane)Fe(NO) is compared to Co(NO) analogs. Acceptors of NO include cobalt octaethylporphyrin and the [(N₂S₂)M] dimeric precursors in the synthesis of the Fe(NO) and Co(NO) biomimetics. Qualitative rates are augmented by a definitive kinetic study finding that rates of NO transfer from (N₂S₂)M(NO) to [(N₂S₂)M']₂ are dependent on M and M' as well as the hydrocarbon N to N and N to S linkers. We conclude that while Fe(NO) and Co(NO) units are similar in chemical stability, minor first coordination sphere differences may favor the former, Fe(NO), consistent with the discovery of Fe(NO), but not Co(NO), in the as-isolated NHase active site.

The discovery of cisplatin (cisPt) as an effective anticancer agent was a milestone in the health industry. Despite its success, undesired side effects and acquired resistance still limit the therapeutic usefulness of cisPt. Intrastrand adduct formation at consecutive purines and structural modifications of DNA caused by platinum(II) complexes are important factors for antitumor efficacy. In this study, we examined amino acid-linked platinum(II) complexes, collectively referred to as AAPt, for antiproliferative activity and ability to induce DNA bending. The antiproliferative activity of one AAPt complex tested against a prostate cancer cell line was comparable to that of cisPt, whereas only activity of the AAPt complex was lower in a normal human prostate cell line. Various AAPt analogues were examined for impact on the structures of DNAs with four different purine dinucleotide target sites (GG, AG, GA, and AA) and compared to the parent cisPt. The roles of side-chain identity, chirality, and coordination type (e.g., (N,O) vs. (N,N)) of AAPt complexes are discussed with respect to DNA adduct formation and ability to induce DNA bending. Although the AAPt complexes display different nucleotide preferences (A for AAPt vs. G for cisPt), DNAs containing GG-platinum adducts display a greater degree of bending compared to DNAs with AA-platinum adducts.

Lipid nanoparticles formed with copolymers are a new and increasingly powerful tool for studying membrane proteins, but the extent to which these systems affect the physical properties of the membrane is not completely understood. This is critical to understanding the caveats of these new systems and screening for structural and functional artifacts that might be caused in the membrane proteins they are used to study. To better understand these potential effects, the fluid properties of dipalmitoylphosphatidylcholine lipid bilayers were examined by electron paramagnetic resonance (EPR) spectroscopy with spin-labeled reporter lipids in either liposomes or incorporated into nanoparticles with the copolymers diisobutylene-maleic acid or styrene maleic acid. Lineshape analysis at varying temperatures reveal a major change in the phase transition behavior of the lipids from a sharp melting curve in liposomes to a more gradual transition in nanoparticles. Electron spin echo envelope modulation (ESEEM) spectroscopy reveals changes in water permeability between mimetic systems, which is further supported by power-saturation measurements showing increased dequenching of spin lipids in diisobutylene-maleic acid nanoparticles compared to maleic acid nanoparticles. These results suggest that diisobutylene-maleic acid nanoparticles may have more physiological fluid properties than styrene-maleic acid nanoparticles when incorporated with saturated phospholipids.