Conserved -Terminal Tail Is Responsible for Membrane Localization and Function of Hemerythrin.

Many bacteria have hemerythrin (Hr) proteins that bind O, including , in which microoxia-induced Hr (Mhr) provide fitness advantages under microoxic conditions. Mhr has a 23 amino-acid extension at its -terminus relative to a well-characterized Hr from , and similar extensions are also found in Hrs from other bacteria. The last 11 amino acids of this extended, -terminal tail are highly conserved in gammaproteobacteria and predicted to form a helix with positively charged and hydrophobic faces.

Applications of the Newly Developed Force-Field Parameters Uncover a Dynamic Nature of Ω-Loop C in the Lys-Ligated Alkaline Form of Cytochrome .

Lys-ligated cytochromes make up an emerging family of heme proteins. Density functional theory calculations on the amine/imidazole-ligated -type ferric heme were employed to develop force-field parameters for molecular dynamics (MD) simulations of structural and dynamic features of these proteins. The new force-field parameters were applied to the alkaline form of yeast -1 cytochrome to rationalize discrepancies resulting from distinct experimental conditions in prior structural studies and to provide insights into the mechanisms of the alkaline transition.

The structure of the diheme cytochrome c from Neisseria gonorrhoeae reveals multiple contributors to tuning reduction potentials.

Cytochrome c (c) is a diheme protein implicated as an electron donor to cbb oxidases in multiple pathogenic bacteria. Despite its prevalence, understanding of how specific structural features of c optimize its function is lacking. The human pathogen Neisseria gonorrhoeae (Ng) thrives in low oxygen environments owing to the activity of its cbb oxidase.

Influence of the Interdomain Interface on Structural and Redox Properties of Multiheme Proteins.

Multiheme proteins are important in energy conversion and biogeochemical cycles of nitrogen and sulfur. A diheme cytochrome () was used as a model to elucidate roles of the interdomain interface on properties of iron centers in its hemes A and B. Isolated monoheme domains -A and -B, together with the full-length diheme and its Met-to-His ligand variants, were characterized by a variety of spectroscopic and stability measurements.

Comparing Properties of Common Bioinorganic Ligands with Switchable Variants of Cytochrome .

Ligand substitution at the metal center is common in catalysis and signal transduction of metalloproteins. Understanding the effects of particular ligands, as well as the polypeptide surrounding, is critical for uncovering mechanisms of these biological processes and exploiting them in the design of bioinspired catalysts and molecular devices. A series of switchable K79G/M80X/F82C (X = Met, His, or Lys) variants of cytochrome (cyt) was employed to directly compare the stability of differently ligated proteins and activation barriers for Met, His, and Lys replacement at the ferric heme iron.

mutant fitness in microoxia is supported by an Anr-regulated oxygen-binding hemerythrin.

strains with loss-of-function mutations in the transcription factor LasR are frequently encountered in the clinic and the environment. Among the characteristics common to LasR-defective (LasR-) strains is increased activity of the transcription factor Anr, relative to their LasR+ counterparts, in low-oxygen conditions. One of the Anr-regulated genes found to be highly induced in LasR- strains was (), which we named for microoxic hemerythrin.

Structure and redox properties of the diheme electron carrier cytochrome c from Pseudomonas aeruginosa.

At low oxygen concentrations, respiration of Pseudomonas aeruginosa (Pa) and other bacteria relies on activity of cytochrome cbb oxidases. A diheme cytochrome c (cyt c) donates electrons to Pa cbb oxidases to enable oxygen reduction and proton pumping by these enzymes. Given the importance of this redox pathway for bacterial pathogenesis, both cyt c and cbb oxidase are potential targets for new antibacterial strategies.

A Heme Propionate Staples the Structure of Cytochrome for Methionine Ligation to the Heme Iron.

Ligand-switch reactions at the heme iron are common in biological systems, but their mechanisms and the features of the polypeptide fold that support dual ligation are not well understood. In cytochrome (cyt ), two low-stability loops (Ω-loop C and Ω-loop D) are connected by the heme propionate HP6. At alkaline pH, the native Met80 ligand from Ω-loop D switches to a Lys residue from the same loop.

Mechanistic Studies of Proton-Coupled Electron Transfer in a Calorimetry Cell.

Mechanistic studies of proton-coupled electron-transfer (PCET) reactions in proteins are complicated by the challenge of following proton transfer (PT) in these large molecules. Herein we describe the use of isothermal titration calorimetry (ITC) to establish proton involvement in protein redox reactions and the identity of PT sites. We validate this approach with three variants of a heme protein cytochrome c (cyt c) and show that the method yields a wealth of thermodynamic information that is important for characterizing PCET reactions, including reduction potentials, redox-dependent p K values, and reaction enthalpies for both electron-transfer (ET) and PT steps.

The K79G Mutation Reshapes the Heme Crevice and Alters Redox Properties of Cytochrome c.

The two roles of cytochrome c (cyt c), in oxidative phosphorylation and apoptosis, critically depend on redox properties of its heme iron center. The K79G mutant has served as a parent protein for a series of mutants of yeast iso-1 cyt c. The mutation preserves the Met80 coordination to the heme iron, as found in WT* (K72A/C102S), and many spectroscopic properties of K79G and WT* are indistinguishable.

Ligation and Reactivity of Methionine-Oxidized Cytochrome c.

Met80, one of the heme iron ligands in cytochrome c (cyt c), is readily oxidized to Met sulfoxide (Met-SO) by several biologically relevant oxidants. The modification has been suggested to affect both the electron-transfer (ET) and apoptotic functions of this metalloprotein. The coordination of the heme iron in Met-oxidized cyt c (Met-SO cyt c) is critical for both of these functions but has remained poorly defined.

Remote Perturbations in Tertiary Contacts Trigger Ligation of Lysine to the Heme Iron in Cytochrome c.

Perturbations in protein structure define the mechanism of allosteric regulation and biological information transfer. In cytochrome c (cyt c), ligation of Met80 to the heme iron is critical for the protein's electron-transfer (ET) function in oxidative phosphorylation and for suppressing its peroxidase activity in apoptosis. The hard base Lys is a better match for the hard ferric iron than the soft base Met is, suggesting the key role of the protein scaffold in favoring Met ligation.

A Compact Structure of Cytochrome c Trapped in a Lysine-Ligated State: Loop Refolding and Functional Implications of a Conformational Switch.

It has been suggested that the alkaline form of cytochrome c (cyt c) regulates function of this protein as an electron carrier in oxidative phosphorylation and as a peroxidase that reacts with cardiolipin (CL) during apoptosis. In this form, Met80, the native ligand to the heme iron, is replaced by a Lys. While it has become clear that the structure of cyt c changes, the extent and sequence of conformational rearrangements associated with this ligand replacement remain a subject of debate.

Control of cytochrome c redox reactivity through off-pathway modifications in the protein hydrogen-bonding network.

Measurements of photoinduced Fe(2+)-to-Ru(3+) electron transfer (ET), supported by theoretical analysis, demonstrate that mutations off the dominant ET pathways can strongly influence the redox reactivity of cytochrome c. The effects arise from the change in the protein dynamics mediated by the intraprotein hydrogen-bonding network.

Redox-dependent stability, protonation, and reactivity of cysteine-bound heme proteins.

Cysteine-bound hemes are key components of many enzymes and biological sensors. Protonation (deprotonation) of the Cys ligand often accompanies redox transformations of these centers. To characterize these phenomena, we have engineered a series of Thr78Cys/Lys79Gly/Met80X mutants of yeast cytochrome c (cyt c) in which Cys78 becomes one of the axial ligands to the heme.

Superior fluorescent probe for detection of cardiolipin.

Cardiolipin (CL) is a unique phospholipid found in mitochondrial inner membrane. It is a key component for mitochondrial function in both respiration and apoptosis. The level of CL is an important parameter for investigating these intracellular events and is a critical indicator of a number of diseases associated with mitochondrial respiratory functions.

Structural transformations of cytochrome c upon interaction with cardiolipin.

Interactions of cytochrome c (cyt c) with cardiolipin (CL) play a critical role in early stages of apoptosis. Upon binding to CL, cyt c undergoes changes in secondary and tertiary structure that lead to a dramatic increase in its peroxidase activity. Insertion of the protein into membranes, insertion of CL acyl chains into the protein interior, and extensive unfolding of cyt c after adsorption to the membrane have been proposed as possible modes for interaction of cyt c with CL.

Becoming a peroxidase: cardiolipin-induced unfolding of cytochrome c.

Interactions of cytochrome c (cyt c) with a unique mitochondrial glycerophospholipid cardiolipin (CL) are relevant for the protein's function in oxidative phosphorylation and apoptosis. Binding to CL-containing membranes promotes cyt c unfolding and dramatically enhances the protein's peroxidase activity, which is critical in early stages of apoptosis. We have employed a collection of seven dansyl variants of horse heart cyt c to probe the sequence of steps in this functional transformation.

Multifaceted effects of ATP on cardiolipin-bound cytochrome c.

Using a collection of dye-labeled cytochrome c (cyt c) variants, we identify transformations of the heterogeneous cardiolipin (CL)-bound cyt c ensemble with added ATP. Distributions of dye-to-heme distances P(r) from time-resolved fluorescence resonance energy transfer show that ATP decreases the population of largely unfolded cyt c conformers, but its effects are distinct from those of a simple salt. The high peroxidase activity of CL-bound cyt c with added ATP suggests binding interactions that favor protein structures with the open heme pocket.

Recombinant expression, biophysical characterization, and cardiolipin-induced changes of two Caenorhabditis elegans cytochrome c proteins.

Cytochrome c (cyt c) is one of the most widely studied biomolecules, but not much is known about this protein from nematodes. Recombinant expression of Caenorhabditis elegans CYC-2.1 and CYC-2.

Origin of the conformational heterogeneity of cardiolipin-bound cytochrome C.

Interactions of cytochrome c (cyt c) with cardiolipin (CL) partially unfold the protein, activating its peroxidase function, a critical event in the execution of apoptosis. However, structural features of the altered protein species in the heterogeneous ensemble are difficult to probe with ensemble averaging. Analyses of the dye-to-heme distance distributions P(r) from time-resolved FRET (TR-FRET) have uncovered two distinct types of CL-bound cyt c conformations, extended and compact.

Changes in the heme ligation during folding of a Geobacter sulfurreducens sensor GSU0935.

Ligand binding and substitution reactions are important for metalloprotein folding and function. The heme sensor of a methyl-accepting chemotaxis GSU0935 is a c-type cytochrome from the bacterium Geobacter sulfurreducens. The heme domain switches one of its axial ligands from H(2)O to a low-spin ligand, presumably Met, upon reduction.

Conformational properties of cardiolipin-bound cytochrome c.

Interactions of cytochrome c (cyt c) with cardiolipin (CL) are important for both electron transfer and apoptotic functions of this protein. A sluggish peroxidase in its native state, when bound to CL, cyt c catalyzes CL peroxidation, which contributes to the protein apoptotic release. The heterogeneous CL-bound cyt c ensemble is difficult to characterize with traditional structural methods and ensemble-averaged probes.

A small fluorophore reporter of protein conformation and redox state.

A new thiol-specific reagent introduces a small bis(methylamino)terephthalic acid fluorophore into proteins. The noninvasive probe with distinct spectroscopic properties offers many advantages for protein labeling, purification, and mechanistic work promising to serve as a powerful tool in studies of protein folding and heme redox reactions.