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Heme Proteins (heme + protein)
Selected AbstractsPurification and cDNA cloning of nitric oxide reductase cytochrome P450nor (CYP55A4) from Trichosporon cutaneumFEBS JOURNAL, Issue 11 2001Li Zhang Cytochrome P450nor is involved in fungal denitrification as nitric oxide (NO) reductase. Although the heme protein has been known to occur in restricted species of fungi that belong to ascomycotina, we have previously suggested that it would also occur in the yeast Trichosporon cutaneum, which is phylogenetically far from those P450nor-producing ascomycetous fungi. Here we isolated and characterized the heme protein from the basidiomycetous yeast T. cutaneum. P450nor of the yeast (TcP450nor) exhibited properties in terms of catalysis, absorption spectrum and molecular mass that are almost identical to those of its counterparts in ascomycetous fungi. We also isolated and sequenced its cDNA. The predicted primary structure of TcP450nor showed high sequence identities (around 65%) to those of other P450nors, indicating that they belong to the same family. TcP450nor protein cofractionated with cytochrome c oxidase by subcellular fractionation and its predicted primary structure contained an extension on its amino terminus that is characteristic of a mitochondrial-targeting signal, indicating that it is a mitochondrial protein like some of the isoforms of other fungi. On the other hand, TcP450nor was unique in that inducers such as nitrate, nitrite, or NO were not required for its production in the cells. The occurrence of P450nor across the subdivisions of eumycota suggests that P450nor and denitrification are distributed more universally among fungi than was previously thought. [source] Distal histidine conformational flexibility in dehaloperoxidase from Amphitrite ornataACTA CRYSTALLOGRAPHICA SECTION D, Issue 1 2009Zuxu Chen The enzyme dehaloperoxidase (DHP) from the terebellid polychaete Amphitrite ornata is a heme protein which has a globin fold but can function as both a hemoglobin and a peroxidase. As a peroxidase, DHP is capable of converting 2,4,6-trihalophenols to the corresponding 2,6-dihaloquinones in the presence of hydrogen peroxide. As a hemoglobin, DHP cycles between the oxy and deoxy states as it reversibly binds oxygen for storage. Here, it is reported that the distal histidine, His55, exhibits conformational flexibility in the deoxy form and is consequently observed in two solvent-exposed conformations more than 9.5,Å away from the heme. These conformations are analogous to the open conformation of sperm whale myoglobin. The heme iron in deoxy ferrous DHP is five-coordinate and has an out-of-plane displacement of 0.25,Å from the heme plane. The observation of five-coordinate heme iron with His55 in a remote solvent-exposed conformation is consistent with the hypothesis that His55 interacts with heme iron ligands through hydrogen bonding in the closed conformation. Since His55 is also displaced by the binding of 4-iodophenol in an internal pocket, these results provide new insight into the correlation between heme iron ligation, molecular binding in the distal pocket and the conformation of the distal histidine in DHP. [source] Cryoradiolytic reduction of crystalline heme proteins: analysis by UV-Vis spectroscopy and X-ray crystallographyJOURNAL OF SYNCHROTRON RADIATION, Issue 1 2007Thorsten Beitlich The X-ray crystallographic analysis of redox-active systems may be complicated by photoreduction. Although radiolytic reduction by the probing X-ray beam may be exploited to generate otherwise short-lived reaction intermediates of metalloproteins, it is generally an undesired feature. Here, the X-ray-induced reduction of the three heme proteins myoglobin, cytochrome P450cam and chloroperoxidase has been followed by on-line UV-Vis absorption spectroscopy. All three systems showed a very rapid reduction of the heme iron. In chloroperoxidase the change of the ionization state from ferric to ferrous heme is associated with a movement of the heme-coordinating water molecule. The influence of the energy of the incident X-ray photons and of the presence of scavengers on the apparent reduction rate of ferric myoglobin crystals was analyzed. [source] Flexibility in Proteins: Tuning the Sensitivity to O2 Diffusion by Varying the Lifetime of a Phosphorescent Sensor in Horseradish Peroxidase,PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 1 2004Janna Nibbs ABSTRACT The heme in horseradish peroxidase (HRP) was replaced by phosphorescent Pt-mesoporphyrin IX (PtMP), which acted as a phosphorescent marker of oxygen quenching and allowed comparison with another probe, Pd-mesoporphyrin IX (Khajehpour et al. (2003) Proteins 53, 656,666). Benzohydroxamic acid (BHA), a competitive inhibitor of the enzyme, was also used to monitor its effects on phosphorescence quenching. With the addition of BHA, in the presence of oxygen, the phosphorescence intensity of the protein increased. In contrast, the addition of BHA, in the absence of oxygen, reduced the phosphorescence intensity of the protein. Kd= 18 ,M when BHA binds to PtMP-HRP. The effect of BHA can be explained by two factors: (1) BHA reduces the accessibility of O2 to the protein interior and (2) BHA itself quenches the phosphorescence. Consistent with this, the oxygen quenching of the phosphorescence of PtMP-HRP gave a quenching constant of kq= 234 mm Hg,1 s,1 in the absence of BHA and kq= 28.7 mm Hg,1 s,1 in the presence of BHA. The quenching rate of BHA is 4000 s,1. The relative quantum yield of the phosphorescence of the Pt derivative is about six times that of the Pd derivative, whereas the phosphorescence lifetime is approximately eight times shorter. The high quantum yield and suitable lifetime make Pt-porphyrins appropriate as sensors of O2 diffusion and flexibility in heme proteins. [source] Review: Studies of ferric heme proteins with highly anisotropic/highly axial low spin (S = 1/2) electron paramagnetic resonance signals with bis-Histidine and histidine-methionine axial iron coordination,BIOPOLYMERS, Issue 12 2009Giorgio Zoppellaro Abstract Six-coordinated heme groups are involved in a large variety of electron transfer reactions because of their ability to exist in both the ferrous (Fe2+) and ferric (Fe3+) state without any large differences in structure. Our studies on hemes coordinated by two histidines (bis-His) and hemes coordinated by histidine and methionine (His-Met) will be reviewed. In both of these coordination environments, the heme core can exhibit ferric low spin (electron paramagnetic resonance EPR) signals with large gmax values (also called Type I, highly anisotropic low spin, or highly axial low spin, HALS species) as well as rhombic EPR (Type II) signals. In bis-His coordinated hemes rhombic and HALS envelopes are related to the orientation of the His groups with respect to each other such that (i) parallel His planes results in a rhombic signal and (ii) perpendicular His planes results in a HALS signal. Correlation between the structure of the heme and its ligands for heme with His-Met axial ligation and ligand-field parameters, as derived from a large series of cytochrome c variants, show, however, that for such a combination of axial ligands there is no clear-cut difference between the large gmax and the "small g -anisotropy" cases as a result of the relative Met-His arrangements. Nonetheless, a new linear correlation links the average shift ,,, of the heme methyl groups with the gmax values. © 2009 Wiley Periodicals, Inc. Biopolymers 91: 1064,1082, 2009. This article was originally published online as an accepted preprint. The "Published Online" date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com [source] H93G myoglobin cavity mutant as versatile template for modeling heme proteins: Magnetic circular dichroism studies of thiolate- and imidazole-ligated complexesBIOPOLYMERS, Issue 4-5 2002John H. Dawson Abstract Recent ligand binding and spectroscopic investigations of the myoglobin H93G cavity mutant are reviewed, revealing it to be a versatile template for the preparation of model heme complexes of defined structure. The H93G myoglobin cavity mutant is shown to be capable of forming mixed ligand adducts because of the difference in accessibility of the two sides of the ferric heme iron. With imidazole bound in the proximal cavity, H93G myoglobin also forms reasonably stable oxyferrous and oxoferryl derivatives, thereby providing a potential system to use for the study of such complexes with proximal ligands other than imidazole. In addition, thiolate-ligated ferric H93G derivatives are described that serve as spectroscopic models for the high-spin ferric state of cytochrome P450. All of the complexes described are characterized with magnetic circular dichroism spectroscopy, and they are compared to the appropriate derivatives of native myoglobin and P450. © 2002 Wiley Periodicals, Inc. Biopolymers (Biospectroscopy) 67: 200,206, 2002 [source] Optimization of Electrochemical and Peroxide-Driven Oxidation of Styrene with Ultrathin Polyion Films Containing Cytochrome P450cam and MyoglobinCHEMBIOCHEM, Issue 1 2003Bernard Munge Abstract The catalytic and electrochemical properties of myoglobin and cytochrome P450camin films constructed with alternate polyion layers were optimized with respect to film thickness, polyion type, and pH. Electrochemical and hydrogen peroxide driven epoxidation of styrene catalyzed by the proteins was used as the test reaction. Ionic synthetic organic polymers such as poly(styrene sulfonate), as opposed to SiO2nanoparticles or DNA, supported the best catalytic and electrochemical performance. Charge transport involving the iron heme proteins was achieved over 40,320 nm depending on the polyion material and is likely to involve electron hopping facilitated by extensive interlayer mixing. However, very thin films (ca. 12,25 nm) gave the largest turnover rates for the catalytic epoxidation of styrene, and thicker films were subject to reactant transport limitations. Classical bell-shaped activity/pH profiles and turnover rates similar to those obtained in solution suggest that films grown layer-by-layer are applicable to turnover rate studies of enzymes for organic oxidations. Major advantages include enhanced enzyme stability and the tiny amount of protein required. [source] | ||||||||||||||||||||||