Coupling of disulfide bond and distal histidine dissociation in human ferrous cytoglobin regulates ligand binding

Earlier kinetics studies on cytoglobin did not assign functional properties to specific structural forms. Here, we used defined monomeric and dimeric forms and cysteine mutants to show that an intramolecular disulfide bond (C38-C83) alters the dissociation rate constant of the intrinsic histidine (H81) (∼1000 fold), thus controlling binding of extrinsic ligands. Through time-resolved spectra we have unequivocally assigned CO binding to hexa- and penta-coordinate forms and have made direct measurement of histidine rebinding following photolysis. We present a model that describes how the cysteine redox state of the monomer controls histidine dissociation rate constants and hence extrinsic ligand binding

Effect of the distal histidine on the peroxidatic activity of monomeric cytoglobin

The reaction of hydrogen peroxide with ferric human cytoglobin and a number of distal histidine variants were studied. The peroxidase activity of the monomeric wildtype protein with an internal disulfide bond, likely to be the form of the protein in vivo, exhibits a high peroxidase-like activity above that of other globins such as myoglobin. Furthermore, the peroxidatic activity of wildtype cytoglobin shows increased resistance to radical-based degradation compared to myoglobin. The ferryl form of wildtype cytoglobin is unstable, but is able to readily oxidize substrates such as guaiacol. In contrast distal histidine mutants of cytoglobin (H81Y and H81V) show very low peroxidase activity but enhanced radical-induced degradation. Therefore, the weakly bound distal histidine appears to modulate ferryl stability and limit haem degradation. These data are consistent with a role of a peroxidase activity of cytoglobin in cell stress response mechanisms.</ns4:p

Strong modulation of nitrite reductase activity of cytoglobin by disulfide bond oxidation: Implications for nitric oxide homeostasis

Globin-mediated nitric oxide (NO) dioxygenase and nitrite reductase activities have been proposed to serve protective functions within the cell by scavenging or generating NO respectively. Cytoglobin has rapid NO dioxygenase activity, similar to other globins, however, the apparent rates of nitrite reductase activity have been reported as slow or negligible. Here we report that the activity of cytoglobin nitrite reductase activity is strongly dependent on the oxidation state of the two surface-exposed cysteine residues. The formation of an intramolecular disulfide bond between cysteines C38 and C83 enhances the nitrite reductase activity by 50-fold over that of the monomer with free sulfhydryl or 140-fold over that of the dimer with intermolecular disulfide bonds. The NO dioxygenase reactivity of cytoglobin is very rapid with or without disulfide bond, however, binding of the distal histidine following dissociation of the nitrate are affected by the presence or absence of the disulfide bond. The nitrite reductase activity reported here for the monomer with intramolecular disulfide is much higher than of those previously reported for other mammalian globins, suggesting a plausible role for this biochemistry in controlling NO homeostasis the cell under oxidative and ischemic conditions

Ultrafast photochemistry of the bc₁ complex

We present a full investigation of ultrafast light-induced events in the membraneous cytochrome bc 1 complex by transient absorption spectroscopy. This energy-transducing complex harbors four redox-active components per monomer: heme c 1 , two 6-coordinate b-hemes and a [2Fe-2S] cluster. Using excitation of these components in different ratios under various excitation conditions, probing in the full visible range and under three well-defined redox conditions, we demonstrate that for all ferrous hemes of the complex photodissociation of axial ligands takes place and that they rebind in 5-7 ps, as in other 6-coordinate heme proteins, including cytoglobin, which is included as a reference in this study. By contrast, the signals are not consistent with photooxidation of the b hemes. This conclusion contrasts with a recent assessment based on a more limited data set. The binding kinetics of internal and external ligands are indicative of a rigid heme environment, consistent with the electron transfer function. We also report, for the first time, photoactivity of the very weakly absorbing iron-sulfur center. This yields the unexpected perspective of studying photochemistry, initiated by excitation of iron-sulfur clusters, in a range of protein complexes

Impact of Nutrition on Non-Relapse Mortality and Acute Graft Versus Host Disease during Allogeneic Hematopoietic Cell Transplantation for Hematologic Malignancies

Abstract The process of allogeneic hematopoietic cell transplantation (HCT) is often associated with poor oral intake and as a result, nutritional status declines. Although it might seem obvious that optimal nutrition is likely to improve outcomes of transplantation, there are no clinical data that directly support this assumption. It is also unclear whether artificial nutrition support (ANS) should be provided as enteral tube feeding (ETF) or parenteral nutrition (PN). In this study we analysed day 100 non-relapse mortality (NRM) and incidence and severity of acute graft versus host disease (GvHD) according to both the route and adequacy of nutritional intake together with other known prognostic factors. A total of 484 patients who underwent HCT for hematological malignancy at a single institution between 2000 and 2014 were included. Myeloablative conditioning was used in 285 (59%) patients, 272 of whom received a TBI based regimen. Reduced intensity conditioning was given to 199 (41%) patients. For the 236 (49%) unrelated donor cell recipients in vivo T-cell depletion with alemtuzumab was used. Myeloablative HCT recipients were advised to have an enteral feeding tube inserted prophylactically at day 1 post HCT. ANS was initiated in 228 (47%) patients who met pre-defined feeding criteria that include actual or anticipated oral intake below 1/3 of estimated requirement for 5 or more days or significant weight loss or low body mass index. Total of 245 (51%) patients had adequate enteral nutrition (EN) either orally (N=198) or with use of ETF (N=47). Patients in whom ETF could not be established received PN (N=148, 31%) in order to provide adequate nutrition. The remaining 91 (19%) patients had inadequate nutrition due to either curtailed ANS (N=33) or a failure to start ANS because of a lack of feeding access via any route (N=58). The effects of patient, disease and transplant factors were studied in univariate analyses on NRM, acute GvHD and engraftment, following which multivariate analyses showed significant associations of NRM with age \u3e 50 years (hazard ratio (HR) 2.3; 95% confidence interval (CI) 1.4 - 3.7; P=0.001); previous autograft (HR 2.4; 95% CI 1.3 - 4.5; P=0.007) and positive recipient CMV serology (HR 1.9; 95% CI 1.1 - 3.2; P=0.019). In addition, HRs were significantly increased in the PN and inadequate nutrition groups compared to those with adequate enteral intake: adequate PN: HR 3.2; 95% CI 1.7 - 6.0, inadequate nutrition: HR 4.4; 95% CI 2.4 - 8.0; all P\u3c0.001 (Figure). There were increased incidences of gastrointestinal GvHD of any stage and acute GvHD \u3e grade 1 in patients who received PN (HR 2.0; 95% CI 1.2 - 3.3; P=0.006, and HR 1.8; 95% CI 1.1 - 3.0; P=0.018, respectively), but not in those with inadequate nutrition compared to adequate EN. Other significant covariates in the model for both increased overall and gut GvHD were the use of myeloablative versus reduced intensity conditioning P=0.001 and P\u3c0.001 and female donor to male recipient versus other combinations P=0.047 and P=0.025 respectively. In conclusion the data show that adequate nutrition during allogeneic HCT is associated with improved non-relapsed mortality at 100 days. Adequate EN is associated with significantly better results for this outcome than adequate PN. Furthermore adequate EN, predominantly via oral intake may be associated with lower incidence of overall and gut GvHD when compared to PN, perhaps because of its ability to maintain gut mucosal integrity and for support of the gastrointestinal tract environment, including gut microflora. Although the retrospective nature of this study can only indicate association, the significant hazard ratios reported warrant further research into optimising enteral nutrition in recipients of HCT. Figure Figure. Disclosures Milojkovic: Novartis: Honoraria; Bristol Myers Squibb: Honoraria; Pfizer: Honoraria; Ariad: Honoraria. Apperley:Incyte: Speakers Bureau; Novartis: Honoraria, Speakers Bureau; Pfizer: Honoraria, Speakers Bureau; Bristol Myers Squibb: Honoraria, Speakers Bureau; Ariad: Honoraria, Speakers Bureau

Impact of route and adequacy of nutritional intake on outcomes of allogeneic haematopoietic cell transplantation for haematologic malignancies.

BACKGROUND: Allogeneic haematopoietic cell transplantation (HCT) is often associated with poor oral intake due to painful mucositis and gastrointestinal sequalae that occur following a preparative regimen of intensive chemotherapy and/or total body radiation. Although attractive to assume that optimal nutrition improves HCT outcomes, there are limited data to support this. It is also unclear whether artificial nutrition support should be provided as enteral tube feeding or parenteral nutrition (PN). METHODS: We analysed day-100 non-relapse mortality (NRM), incidence of acute graft-versus-host disease (GvHD), acute gastrointestinal GvHD, 5-year survival and GvHD-free/relapse-free survival (GRFS) according to both route and adequacy of nutritional intake prior to neutrophil engraftment, together with other known prognostic factors, in a retrospective cohort of 484 patients who underwent allogeneic HCT for haematologic malignancy between 2000 and 2014. RESULTS: Multivariate analyses showed increased NRM with inadequate nutrition (hazard ratio (HR) 4.1; 95% confidence interval (CI) 2.2-7.2) and adequate PN (HR 2.9; 95% CI 1.6-5.4) compared to adequate enteral nutrition (EN) both P < .001. There were increased incidences of gastrointestinal GvHD of any stage and all GvHD ≥ grade 2 in patients who received PN (odds ratio (OR) 2.0; 95% CI 1.2-3.3; P = .006, and OR 1.8; 95% CI 1.1-3.0; P = .018, respectively), compared to adequate EN. Patients who received adequate PN and inadequate nutrition also had reduced probabilities of survival and GRFS at 5 years. CONCLUSION: Adequate EN during the early transplantation course is associated with reduced NRM, improved survival and GRFS at 5 years. Furthermore, adequate EN is associated with lower incidence of overall and gut acute GvHD than PN, perhaps because of its ability to maintain mucosal integrity, modulate the immune response to intensive chemo/radiotherapy and support the gastrointestinal tract environment, including gut microflora

Cytoglobin ligand binding regulated by changing haem-co-ordination in response to intramolecular disulfide bond formation and lipid interaction

Cytoglobin (Cygb) is a hexa-co-ordinate haem protein from the globin superfamily with a physiological function that is unclear. We have previously reported that the haem co-ordination is changed in the presence of lipids, potentially transforming the redox properties of the protein and hence the function of Cygb in vivo. Recent research suggests that the protein can exist in a number of states depending on the integrity and position of disulfide bonds. In the present study, we show that the monomeric protein with an internal disulfide bond between the two cysteine residues Cys38 and Cys83, interacts with lipids to induce a change in haem co-ordination. The dimeric protein with intermolecular disulfide bonds and monomeric protein without an intramolecular disulfide bond does not exhibit these changes in haem co-ordination. Furthermore, monomeric Cygb with an intramolecular disulfide bond has significantly different properties, oxidizing lipid membranes and binding ligands more rapidly as compared with the other forms of the protein. The redox state of these cysteine residues in vivo is therefore highly significant and may be a mechanism to modulate the biochemical properties of the haem under conditions of stress.</jats:p