Highly selective ligand binding by Methylophilus methylotrophus cytochrome c''

Molecular Details on Multiple Cofactor Containing Redox Metalloproteins Revealed by Infrared and Resonance Raman Spectroscopies

Vibrational spectroscopy and in particular, resonance Raman (RR) spectroscopy, can provide molecular details on metalloproteins containing multiple cofactors, which are often challenging for other spectroscopies. Due to distinct spectroscopic fingerprints, RR spectroscopy has a unique capacity to monitor simultaneously and independently different metal cofactors that can have particular roles in metalloproteins. These include e.g., (i) different types of hemes, for instance hemes c, a and a3 in caa3-type oxygen reductases, (ii) distinct spin populations, such as electron transfer (ET) low-spin (LS) and catalytic high-spin (HS) hemes in nitrite reductases, (iii) different types of Fe-S clusters, such as 3Fe-4S and 4Fe-4S centers in di-cluster ferredoxins, and (iv) bi-metallic center and ET Fe-S clusters in hydrogenases. IR spectroscopy can provide unmatched molecular details on specific enzymes like hydrogenases that possess catalytic centers coordinated by CO and CN- ligands, which exhibit spectrally well separated IR bands. This article reviews the work on metalloproteins for which vibrational spectroscopy has ensured advances in understanding structural and mechanistic properties, including multiple heme-containing proteins, such as nitrite reductases that house a notable total of 28 hemes in a functional unit, respiratory chain complexes, and hydrogenases that carry out the most fundamental functions in cells.

Magnetic Nanospheres Encapsulated by Mesoporous Copper Oxide Shell for Selective Isolation of Hemoglobin

A novel strategy for the preparation of magnetic nanospheres encapsulated by mesoporous copper oxide shell, shortly termed as Fe₃O₄@mCuO, is reported via the calcination of Cu(NH₃)₄(NO₃)₂ into continuous mesoporous CuO shell onto the surface of Fe₃O₄ nanoparticles. The magnetic nanospheres are characterized to possess stable core-shell structure with a crystalline mesoporous CuO layer, exhibiting a CuO loading content of 25.2 ± 1.1% along with a favorable magnetic susceptibility. Fe₃O₄@mCuO nanospheres exhibit favorable selectivity on the adsorption of hemoglobin with a high adsorption capacity of up to 1162.5 mg g^-1. After adsorption, the high magnetic susceptibility allows convenient separation of the nanospheres by an external magnet. The retained hemoglobin could be readily recovered by using 0.5% (m/v) sodium dodecyl sulfate (SDS) as stripping reagent, providing a recovery of 78%. Circular dichroism spectra illustrate virtually no change in the conformation of hemoglobin after the process of adsorption/desorption. Fe₃O₄@mCuO nanospheres are further applied for the selective isolation of hemoglobin from human whole blood, achieving high-purity hemoglobin as demonstrated by SDS-PAGE (polyacrylamide gel electrophoresis) assays.

SERR Spectroelectrochemical Study of Cytochrome cd1 Nitrite Reductase Co-Immobilized with Physiological Redox Partner Cytochrome c552 on Biocompatible Metal Electrodes

Cytochrome cd1 nitrite reductases (cd₁NiRs) catalyze the one-electron reduction of nitrite to nitric oxide. Due to their catalytic reaction, cd₁NiRs are regarded as promising components for biosensing, bioremediation and biotechnological applications. Motivated by earlier findings that catalytic activity of cd₁NiR from Marinobacter hydrocarbonoclasticus (Mhcd₁) depends on the presence of its physiological redox partner, cytochrome c₅₅₂ (cyt c₅₅₂), we show here a detailed surface enhanced resonance Raman characterization of Mhcd₁ and cyt c₅₅₂ attached to biocompatible electrodes in conditions which allow direct electron transfer between the conducting support and immobilized proteins. Mhcd₁ and cyt c552 are co-immobilized on silver electrodes coated with self-assembled monolayers (SAMs) and the electrocatalytic activity of Ag // SAM // Mhcd₁ // cyt c₅₅₂ and Ag // SAM // cyt c₅₅₂ // Mhcd₁ constructs is tested in the presence of nitrite. Simultaneous evaluation of structural and thermodynamic properties of the immobilized proteins reveals that cyt c₅₅₂ retains its native properties, while the redox potential of apparently intact Mhcd₁ undergoes a ~150 mV negative shift upon adsorption. Neither of the immobilization strategies results in an active Mhcd₁, reinforcing the idea that subtle and very specific interactions between Mhcd₁ and cyt c₅₅₂ govern efficient intermolecular electron transfer and catalytic activity of Mhcd₁.

Cytochromes c': Structure, Reactivity and Relevance to Haem-Based Gas Sensing

Cytochromes c' are a group of class IIa cytochromes with pentacoordinate haem centres and are found in photosynthetic, denitrifying and methanotrophic bacteria. Their function remains unclear, although roles in nitric oxide (NO) trafficking during denitrification or in cellular defence against nitrosoative stress have been proposed. Cytochromes c' are typically dimeric with each c-type haem-containing monomer folding as a four-α-helix bundle. Their hydrophobic and crowded distal sites impose severe restrictions on the binding of distal ligands, including diatomic gases. By contrast, NO binds to the proximal haem face in a similar manner to that of the eukaryotic NO sensor, soluble guanylate cyclase and bacterial analogues. In this review, we focus on how structural features of cytochromes c' influence haem spectroscopy and reactivity with NO, CO and O2. We also discuss the relevance of cytochrome c' to understanding the mechanisms of gas binding to haem-based sensor proteins.

Constructing a man-made c-type cytochrome maquette in vivo: electron transfer, oxygen transport and conversion to a photoactive light harvesting maquette

The successful use of man-made proteins to advance synthetic biology requires both the fabrication of functional artificial proteins in a living environment, and the ability of these proteins to interact productively with other proteins and substrates in that environment. Proteins made by the maquette method integrate sophisticated oxidoreductase function into evolutionarily naive, non-computationally designed protein constructs with sequences that are entirely unrelated to any natural protein. Nevertheless, we show here that we can efficiently interface with the natural cellular machinery that covalently incorporates heme into natural cytochromes c to produce in vivo an artificial c-type cytochrome maquette. Furthermore, this c-type cytochrome maquette is designed with a displaceable histidine heme ligand that opens to allow functional oxygen binding, the primary event in more sophisticated functions ranging from oxygen storage and transport to catalytic hydroxylation. To exploit the range of functions that comes from the freedom to bind a variety of redox cofactors within a single maquette framework, this c-type cytochrome maquette is designed with a second, non-heme C, tetrapyrrole binding site, enabling the construction of an elementary electron transport chain, and when the heme C iron is replaced with zinc to create a Zn porphyrin, a light-activatable artificial redox protein. The work we describe here represents a major advance in de novo protein design, offering a robust platform for new c-type heme based oxidoreductase designs and an equally important proof-of-principle that cofactor-equipped man-made proteins can be expressed in living cells, paving the way for constructing functionally useful man-made proteins in vivo.