A Soret Marker Band for Four-Coordinate Ferric Heme Proteins from Absorption Spectra of Isolated Fe(III)-Heme+ and Fe(III)-Heme+(His) Ions in Vacuo

In vitro Production of Hemin-Based Artificial Metalloenzymes

Developing enzyme alternatives is pivotal to improving and enabling new processes in biotechnology and industry. Artificial metalloenzymes (ArMs) are combinations of protein scaffolds with metal elements, such as metal nanoclusters or metal-containing molecules with specific catalytic properties, which can be customized. Here, we engineered an ArM based on the consensus tetratricopeptide repeat (CTPR) scaffold by introducing a unique histidine residue to coordinate the hemin cofactor. Our results show that this engineered system exhibits robust peroxidase-like catalytic activity driven by the hemin. The expression of the scaffold and subsequent coordination of hemin was achieved by recombinant expression in bulk and through in vitro transcription and translation systems in water-in-oil drops. The ability to synthesize this system in emulsio paves the way to improve its properties by means of droplet microfluidic screenings, facilitating the exploration of the protein combinatorial space to discover improved or novel catalytic activities.

Network pharmacology-based dissection of the underlying mechanisms of dyspnoea induced by zedoary turmeric oil

Zedoary turmeric oil (ZTO) has been widely used in clinic. However, the unpleasant induced dyspnoea inevitably impedes its clinical application. Thus, it is urgent to elucidate the mechanism underlying the ZTO-induced dyspnoea. In this study, network pharmacology was firstly performed to search the clue of ZTO-induced dyspnoea. The key target genes of ZTO-induced dyspnoea were analysed using GO enrichment analysis and KEGG pathway analysis. GO analysis suggested that haem binding could be a key molecular function involved in ZTO-induced dyspnoea. Hence, the haemoglobin (Hb) was focused for its oxygen-carrying capacity with haem as its critical component binding to the oxygen. Ultraviolet-visible absorption spectrum indicated that the ZTO injection (ZTOI) perturbed the Soret band of Hb, suggesting an interaction between ZTO and Hb. GC-MS analysis revealed that β-elemene, germacrone, curdione and furanodiene were main components of ZTOI. Molecular docking was used to illustrate the high affinity between representative sesquiterpenes and Hb, which was finally confirmed by surface plasmon resonance, suggesting their potential roles in dyspnoea by ZTO. Following a network pharmacology-driven strategy, our study revealed an intervened Hb-based mechanism underlying the ZTO-induced dyspnoea, providing a reference for elucidating mechanism underlying adverse drug reactions of herbal medicines in clinic.

Ionization and Photofragmentation of Isolated Metalloporphyrin Cations Investigated by VUV Action Spectroscopy*

We investigated the photoionization and fragmentation of isolated metal protoporphyrin IX cations (MPPIX+ with M=Fe, Co, Zn) by means of vacuum-ultraviolet (VUV) action spectroscopy in the energy range of 8.5-35 eV. Experiments were carried out in the gas phase by interfacing an electrospray ionization tandem mass spectrometer with a synchrotron beamline. The mass spectra and partial ion yields show that photoexcitation of the precursor ions predominantly leads to . CH2 COOH radical side-chain losses of the macrocycle with additional methyl radical (. CH3 ) side-chain losses. Ionization, in contrast, leads to the formation of the intact ionized precursor and various doubly charged fragments which are mostly due to side-chain cleavages. Although statistical fragmentation dominates, we found evidence for non-statistical processes such as new fragments involving for example single and double H2 O losses, indicating that different relaxation mechanisms are at play upon photoionization compared to photoexcitation. The measured ionization energies were 9.6±0.2 eV, 9.4±0.2 eV and 9.6±0.2 eV for FePPIX+ , CoPPIX+ and ZnPPIX+ , respectively.

The electronic structure and deexcitation pathways of an isolated metalloporphyrin ion resolved by metal L-edge spectroscopy

The local electronic structure of the metal-active site and the deexcitation pathways of metalloporphyrins are crucial for numerous applications but difficult to access by commonly employed techniques. Here, we applied near-edge X-ray absorption mass spectrometry and quantum-mechanical restricted active space calculations to investigate the electronic structure of the metal-active site of the isolated cobalt(iii) protoporphyrin IX cation (CoPPIX+) and its deexcitation pathways upon resonant absorption at the cobalt L-edge. The experiments were carried out in the gas phase, thus allowing for control over the chemical state and molecular environment of the metalloporphyrin. The obtained mass spectra reveal that resonant excitations of CoPPIX+ at the cobalt L3-edge lead predominantly to the formation of the intact radical dication and doubly charged fragments through losses of charged and neutral side chains from the macrocycle. The comparison between experiment and theory shows that CoPPIX+ is in a 3A2g triplet ground state and that competing excitations to metal-centred non-bonding and antibonding σ* molecular orbitals lead to distinct deexcitation pathways.

Ion Mobility Measurements of Multianionic Metalloporphyrin Dimers: Structural Changes Induced by Countercation Exchange

We present gas-phase structures of dimers of Mn^III and Fe^III meso-tetra(4-sulfonatophenyl)porphyrin multianions with various amounts of sodium and hydrogen counterions. The structural assignments are achieved by combining mass spectrometry, ion mobility measurements, quantum chemical calculations, and trajectory method collision cross section calculations. For a common charge state, we observe significant topological variations in the dimer structures of [(MTPPS)₂+nX]^(6-n)- (M=Mn^III, Fe^III; X=H, Na; n = 1-3) induced by replacing hydrogen counterions by sodium. For sodium, the dimer structures are much more compact, a finding that can be rationalized by the stronger interactions of the sodium cations with the anionic sulfonic acid groups of the porphyrins as compared to hydrogen. Graphical Abstract ᅟ.

Cryo IR Spectroscopy of [Hemin]+ Complexes in Isolation

We present cryo IR spectra of isolated [Hemin]⁺ adducts with CO, N₂, and O₂ ([Hemin(CO)₁]⁺, [Hemin(CO)₂]⁺, [Hemin(¹⁴N₂)]⁺, [Hemin(¹⁵N₂)]⁺, and [Hemin(O₂)]⁺). Well resolved bands allow for the elucidation of structure and spin multiplicity in conjunction with density functional (DFT) calculations. There is a quartet spin state for the N₂ and CO adducts and a sextet spin state for the O₂ adduct, where the O₂ retains its triplet state. The double CO adsorption induces significant changes in the vibrational patterns of the IR spectra, which we take as strong evidence for a spin quenching into a doublet. Our study characterizes [Hemin]⁺, which is the Fe³⁺ oxidation product of heme that is of ubiquitous presence in hemeproteins.

Cj1386, an atypical hemin-binding protein, mediates hemin trafficking to KatA in Campylobacter jejuni

Catalase enzymes detoxify H2O2 by the dismutation of H2O2 into O2 and H2O through the use of hemin cofactors. While the structure and biochemical properties of catalase enzymes have been well characterized over many decades of research, it remained unclear how catalases acquire hemin. We have previously reported that Cj1386 is essential for ensuring proper hemin content in Campylobacter jejuni catalase (KatA) (A. Flint, Y. Q. Sun, and A. Stintzi, J Bacteriol 194: 334-345, 2012). In this report, an in-depth molecular characterization of Cj1386 was performed to elucidate the mechanistic details of this association. Coimmunoprecipitation assays revealed that KatA-Cj1386 transiently interact in vivo, and UV-visible spectroscopy demonstrated that purified Cj1386 protein binds hemin. Furthermore, hemin titration experiments determined that hemin binds to Cj1386 in a 1:1 ratio with hexacoordinate hemin binding. Mutagenesis of potential hemin-coordinating residues in Cj1386 showed that tyrosine 57 was essential for hemin coordination when Cj1386 was overexpressed in Escherichia coli. The importance of tyrosine 57 in hemin trafficking in vivo was confirmed by introducing the cj1386(Y57A) allele into a C. jejuni Δcj1386 mutant background. The cj1386(Y57A) mutation resulted in increased sensitivity toward H2O2 relative to the wild type, suggesting that KatA was not functional in this strain. In support of this finding, KatA immunoprecipitated from the Δcj1386+cj1386(Y57A) mutant had significantly reduced hemin content compared to that of the cj1386(WT) background. Overall, these findings indicate that Cj1386 is involved in directly trafficking hemin to KatA and that tyrosine 57 plays a key role in this function.

Gas-phase spectroscopy of ferric heme-NO complexes

Weakly bound complexes between ferric heme cations and NO were synthesised in the gas phase from ion-molecule reactions, and their absorption measured based on photodissociation yields. The Soret band, which serves as an important marker band for heme-protein spectroscopy, is maximal at 357±5 nm and significantly blue-shifted compared to ferric heme nitrosyl proteins (maxima between 408 and 422 nm). This is in stark contrast to the Q-band absorption where the protein microenvironment is nearly innocent in perturbing the electronic structure of the porphyrin macrocycle. Photodissociation is primarily through loss of NO. In contrast to the Q-band region, two-photon absorption was seen in the Soret band despite NO loss only requiring ∼1 eV. A model based on intersystem crossing to a long-lived triplet state where a barrier has to be surmounted is suggested. Finally, we summarise the measured absorption maxima of heme and its complexes with amino acids and NO.

Soret Band of the Gas-Phase Ferri-Cytochrome c

We report the first visible spectrum of a heme-protein in the gas phase. The aim of this work was to provide a reference for the optical absorption of an isolated heme-protein to better understand the influence of protein conformation and fluctuation and of solvent on its optical properties. After laser irradiation of gas-phase cytochrome c (cyt c), electron emission is observed. Electron photodetachment yield of cyt c 6- was recorded in the region of the Soret band of the porphyrin group, showing a maximum at 410 nm. Our results are compared with optical spectra of gas-phase heme and of cyt c in solution. We discuss the influence of the polypeptide chain and of the solvent on both the position and the broadening of the Soret band. Action spectrum of gas-phase cyt c is close to the absorption of native cyt c in solution, suggesting an efficient protection of the heme group from solvent accessibility by the polypeptide chain and similar interactions between the two moieties in solution and the gas phase.