An official website of the United States government
Abstract The degree by which metalloproteins partially regulate net charge (Z) upon electron transfer (ET) was recently measured for the first time using “protein charge ladders” of azurin, cytochrome c, and myoglobin [Angew. Chem. Int. Ed.2018,57(19), 5364–5368;Angew. Chem.2018,130, 5462–5466]. Here, we show that Cu, Zn superoxide dismutase (SOD1) is unique among proteins in its ability to resist changes in net charge upon single ET (e.g., ΔZET(SOD1)=0.05±0.08 per electron, compared to ΔZET(Cyt‐c)=1.19±0.02). This total regulation of net charge by SOD1 is attributed to the protonation of the bridging histidine upon copper reduction, yielding redox centers that are isoelectric at both copper oxidation states. Charge regulation by SOD1 would prevent long range coulombic perturbations to residue pKa’s upon ET at copper, allowing SOD1’s “electrostatic loop” to attract superoxide with equal affinity (at both redox states of copper) during diffusion‐limited reduction and oxidation of superoxide.
more »
« less
This content will become publicly available on March 1, 2026
Cytochromes P460 and c′-β: exploiting a novel fold for multiple functions
Abstract Two related classes of ligand-binding hemec-containing proteins with a high degree of structural homology have been identified and characterized over recent decades: cytochromes P460 (cyts P460), defined by an unusual heme-lysine cross-link, and cytochromesc′-β (cytsc′-β), containing a canonicalc-heme without the lysine cross-link. The shared protein fold of the cyt P460-cytc′-β superfamily can accommodate a variety of heme environments with entirely different reactivities. On the one hand, cyts P460 with polar distal pockets have been shown to oxidize NH2OH to NO and/or N2O via proton-coupled electron transfer. On the other hand, cytsc′-β with hydrophobic distal pockets have a proposed gas binding function similar to the unrelated, but more extensively characterized, alpha helical cytochromesc′. Recent studies have also identified ‘halfway house’ proteins (cyts P460 with non-polar heme pockets and cytsc′-β with polar distal heme pockets) with functions yet to be resolved. Here, we review the structural, spectroscopic and enzymatic properties of the cyt P460-cytc′-β superfamily with a view to understanding the structural determinants of their different functional properties. Graphical abstract
more »
« less
- Award ID(s):
- 1921670
- PAR ID:
- 10615536
- Publisher / Repository:
- Springer
- Date Published:
- Journal Name:
- JBIC Journal of Biological Inorganic Chemistry
- Volume:
- 30
- Issue:
- 2
- ISSN:
- 1432-1327
- Page Range / eLocation ID:
- 181 to 207
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract Thesynandantiisomers of [FeIV(O)(TMC)]2+(TMC=tetramethylcyclam) represent the first isolated pair of synthetic non‐heme oxoiron(IV) complexes with identical ligand topology, differing only in the position of the oxo unit bound to the iron center. Both isomers have previously been characterized. Reported here is that thesynisomer [FeIV(Osyn)(TMC)(NCMe)]2+(2) converts into itsantiform [FeIV(Oanti)(TMC)(NCMe)]2+(1) in MeCN, an isomerization facilitated by water and monitored most readily by1H NMR and Raman spectroscopy. Indeed, when H218O is introduced to2, the nascent1becomes18O‐labeled. These results provide compelling evidence for a mechanism involving direct binding of a water moleculetransto the oxo atom in2with subsequent oxo–hydroxo tautomerism for its incorporation as the oxo atom of1. The nonplanar nature of the TMC supporting ligand makes this isomerization an irreversible transformation, unlike for their planar heme counterparts.more » « less
-
Calcium‐Ion Binding Mediates the Reversible Interconversion of Cis and Trans Peroxido Dicopper CoresAbstract Coupled dinuclear copper oxygen cores (Cu2O2) featured in type III copper proteins (hemocyanin, tyrosinase, catechol oxidase) are vital for O2transport and substrate oxidation in many organisms.μ‐1,2‐cisperoxido dicopper cores (CP) have been proposed as key structures in the early stages of O2binding in these proteins; their reversible isomerization to other Cu2O2cores are directly relevant to enzyme function. Despite the relevance of such species to type III copper proteins and the broader interest in the properties and reactivity of bimetallicCPcores in biological and synthetic systems, the properties and reactivity ofCPCu2O2species remain largely unexplored. Herein, we report the reversible interconversion ofμ‐1,2‐transperoxido (TP) andCPdicopper cores. CaIImediates this process by reversible binding at the Cu2O2core, highlighting the unique capability for metal‐ion binding events to stabilize novel reactive fragments and control O2activation in biomimetic systems.more » « less
-
Abstract Flavodiiron NO reductases (FNORs) are important enzymes in microbial pathogenesis, as they equip microbes with resistance to the human immune defense agent nitric oxide (NO). Despite many efforts, intermediates that would provide insight into how the non‐heme diiron active sites of FNORs reduce NO to N2O could not be identified. Computations predict that iron‐hyponitrite complexes are the key species, leading from NO to N2O. However, the coordination chemistry of non‐heme iron centers with hyponitrite is largely unknown. In this study, we report the reactivity of two non‐heme iron complexes with preformed hyponitrite. In the case of [Fe(TPA)(CH3CN)2](OTf)2, cleavage of hyponitrite and formation of an Fe2(NO)2diamond core is observed. With less Lewis‐acidic [Fe2(BMPA‐PhO)2(OTf)2] (2), reaction with Na2N2O2in polar aprotic solvent leads to the formation of a red complex,3. X‐ray crystallography shows that3is a tetranuclear iron‐hyponitrite complex, [{Fe2(BMPA‐PhO)2}2(μ‐N2O2)](OTf)2, with a unique hyponitrite binding mode. This species provided the unique opportunity to us to study the interaction of hyponitrite with non‐heme iron centers and the reactivity of the bound hyponitrite ligand. Here, either protonation or oxidation of3is found to induce N2O formation, supporting the hypothesis that hyponitrite is a viable intermediate in NO reduction.more » « less
-
Cortajarena, Aitziber L (Ed.)Abstract Palladin is an actin‐binding protein that accelerates actin polymerization and is linked to the metastasis of several types of cancer. Previously, three lysine residues in an immunoglobulin‐like domain of palladin have been identified as essential for actin binding. However, it is still unknown where palladin binds to F‐actin. Evidence that palladin binds to the sides of actin filaments to facilitate branching is supported by our previous study showing that palladin was able to compensate for Arp2/3 in the formation ofListeriaactin comet tails. Here, we used chemical crosslinking to covalently link palladin and F‐actin residues based on spatial proximity. Samples were then enzymatically digested, separated by liquid chromatography, and analyzed by tandem mass spectrometry. Peptides containing the crosslinks and specific residues involved were then identified for input to the HADDOCK docking server to model the most likely binding conformation. Small‐angle x‐ray scattering was used to provide further insight into palladin flexibility and the binding interface, and NMR spectra identified potential interactions between palladin's Ig domains. Our final structural model of the F‐actin:palladin complex revealed how palladin interacts with and stabilizes F‐actin at the interface between two actin monomers. Three actin residues that were identified in this study also appear commonly in the actin‐binding interface with other proteins such as myotilin, myosin, and tropomodulin. An accurate structural representation of the complex between palladin and actin extends our understanding of palladin's role in promoting cancer metastasis through the regulation of actin dynamics.more » « less
