Inhibition of Heme Uptake inPseudomonas aeruginosaby its Hemophore (HasAp) Bound to Synthetic Metal Complexes

Design and characterization of porphyrin-based photosensitizing metalloproteins integrated with artificial metalloenzymes for photocatalytic hydrogen production

Hydrogen is regarded as a promising alternative to fossil fuels. A desirable method of its generation is via photocatalysis, combining photosensitizers and hydrogen-evolution catalysts in the presence of an electron donor. Inspired by natural photosynthesis, we designed photosensitizing artificial metalloproteins (ArMs) and integrated them with ArM-based catalysts for photocatalytic hydrogen production from water. Metal porphyrins based on protoporphyrin IX (PPIX) were employed as they are naturally abundant and are effective both as photosensitizers and hydrogen-evolution catalysts. Photosensitizing proteins were created by binding zinc (Zn)PPIX or ruthenium (Ru)PPIX to the haem acquisition system A from Pseudomonas aeruginosa (HasAp). The photosensitizer ArMs were combined with cobalt (Co)PPIX-myoglobin (Mb) or free CoPPIX as hydrogen evolution catalysts. We found that free CoPPIX could replace ZnPPIX or RuPPIX in HasAp, forming CoPPIX-HasAp or RuPPIX-CoPPIX-HasAp complexes with enhanced stability compared to CoPPIX-Mb. Photocatalytic hydrogen production was achieved upon irradiation at 435 nm (ZnPPIX) or 385 nm (RuPPIX), using methyl viologen as an electron carrier and triethanolamine as an electron donor. The ZnPPIX-HasAp/CoPPIX-HasAp system remained intact and active for approximately 42 h, while Ru-based systems that were excited by UV light, exhibited signs of protein cleavage upon prolonged irradiation. These results demonstrate the potential of integrating porphyrin-based ArMs for photosensitization and hydrogen evolution, with HasAp providing a robust scaffold for sustained photocatalytic activity.

A screening method for binding synthetic metallo-complexes to haem proteins

The introduction of a second coordination sphere, in the form of a protein scaffold, to synthetic catalysts can be beneficial for their reactivity and substrate selectivity. Here we present semi-native polyacrylamide gel electrophoresis (semi-native PAGE) as a rapid screening method for studying metal complex-protein interactions. Such a screening is generally performed using electron spray ionization mass spectrometry (ESI-MS) and/or UV-Vis spectroscopy. Semi-native PAGE analysis has the advantage that it does not rely on spectral changes of the metal complex upon protein interaction and can be applied for high-throughput screening and optimization of complex binding. In semi-native PAGE non-denatured protein samples are loaded on a gel containing sodium dodecyl sulphate (SDS), leading to separation based on differences in structural stability. Semi-native PAGE gel runs of catalyst-protein mixtures were compared to gel runs obtained with native and denaturing PAGE. ESI-MS was additionally realised to confirm protein-complex binding. The general applicability of semi-native PAGE was investigated by screening the binding of various cobalt- and ruthenium-based compounds to three types of haem proteins.

A Heme-Acquisition Protein Reconstructed with a Cobalt 5-Oxaporphyrinium Cation and Its Growth-Inhibition Activity Toward Multidrug-Resistant Pseudomonas aeruginosa

Using artificial hemes for the reconstruction of natural heme proteins represents a fascinating approach to enhance the bioactivity of the latter. Here, we report the synthesis of various metal 5-oxaporphyrinium cations as cofactors, and a cobalt 5-oxaporphyrinium cation was successfully incorporated into the heme-acquisition protein (HasA) secreted by Pseudomonas aeruginosa. We hypothesize that the oxaporphyrinium cation strongly bound to the HasA-specific outer membrane receptor (HasR) due to its cationic charge, which prevents the subsequent acquisition of heme. In fact, the reconstructed HasA inhibited the growth of Pseudomonas aeruginosa and even of multidrug-resistant P. aeruginosa.

Chemical and Biological Aspects of Nutritional Immunity-Perspectives for New Anti-Infectives that Target Iron Uptake Systems

Upon bacterial infection, one of the defense mechanisms of the host is the withdrawal of essential metal ions, in particular iron, which leads to "nutritional immunity". However, bacteria have evolved strategies to overcome iron starvation, for example, by stealing iron from the host or other bacteria through specific iron chelators with high binding affinity. Fortunately, these complex interactions between the host and pathogen that lead to metal homeostasis provide several opportunities for interception and, thus, allow the development of novel antibacterial compounds. This Review focuses on iron, discusses recent highlights, and gives some future perspectives which are relevant in the fight against antibiotic resistance.