Assessment of the potential value of plasma Torque Teno virus DNA load monitoring to predict cytomegalovirus DNAemia in patients with hematological malignancies treated with small molecule inhibitors: A proof-of-concept study.

It is unknown whether Torque Teno virus (TTV) DNA load monitoring could anticipate the development of infectious events in hematological patients undergoing treatment with small molecular targeting agents. We characterized the kinetics of plasma TTV DNA in patients treated with ibrutinib or ruxolitinib and assessed whether TTV DNA load monitoring could predict the occurrence of Cytomegalovirus (CMV) DNAemia or the magnitude of CMV-specific T-cell responses. Multicenter, retrospective, observational study, recruiting 20 patients treated with ibrutinib and 21 with ruxolitinib. Plasma TTV and CMV DNA loads were quantified by real-time PCR at baseline and days +15, +30, +45, +60, +75, +90, +120, +150, and +180 after treatment inception. Enumeration of CMV-specific interferon-γ (IFN-γ)-producing CD8+ and CD4+ T-cells in whole blood was performed by flow cytometry. Median TTV DNA load in ibrutinib-treated patients increased significantly (p = 0.025) from baseline (median: 5.76 log10 copies/mL) to day +120 (median: 7.83 log10 copies/mL). A moderate inverse correlation (Rho = -0.46; p < 0.001) was found between TTV DNA load and absolute lymphocyte count. In ruxolitinib-treated patients, TTV DNA load quantified at baseline was not significantly different from that measured after treatment inception (p ≥ 0.12). TTV DNA load was not predictive of the subsequent occurrence of CMV DNAemia in either patient group. No correlation was observed between TTV DNA loads and CMV-specific IFN-γ-producing CD8+ and CD4+ T-cell counts in either patient group. The data did not support the hypothesis that TTV DNA load monitoring in hematological patients treated with ibrutinib or ruxolitinib could be useful to predict either the occurrence of CMV DNAemia or the level of CMV-specific T-cell reconstitution; nevertheless, due to the small sample size, further studies involving larger cohorts are warranted to elucidate this issue.

Active Role of the Buffer in the Proton-Coupled Electron Transfer of Immobilized Iron Porphyrins.

Evaluation of the proton-coupled electron transfer thermodynamics of immobilized hemin is challenging due to the disparity of its electrochemical titration curves reported in the literature. Deviations from the one-electron, one-proton transfer at circumneutral pHs have been commonly ascribed to either the formation of dimeric species or the ionization of a second iron-bound water molecule. Herein, however, we report on non-idealities in the more acidic region, whose onset and extent vary with the nature and concentration of the commonly used phosphate and acetate buffers. It is shown that these deviations originate in the ligand-exchange binding between the oxidized aquo-hemin complex and the anionic components of the buffer, so that they are restricted to the pH interval where these forms coexist. A stepwise approach was developed to quantify unambiguously the apparent and intrinsic binding equilibrium constants. The apparent binding equilibrium constant exhibits a peak-shaped pH dependence, whose maximum is located at approximately the midpoint between the pKa of the iron-bound water and the first pKa of the buffer, and its magnitude is greater for the phosphate than for the acetate buffer. But strikingly, the opposite trend was found for the magnitude of the intrinsic binding equilibrium constants determined from the apparent ones, due to the different relative locations of the phosphoric and acetic pKa values with respect to that of the oxidized aquo-hemin. To probe the role of the heme propionic residues, a similar study was carried out with a propionic-free iron porphyrin containing eight ethyl residues. These substituents decrease the acidity of the iron-bound water, strengthen the iron(III)-acetate binding, weaken the iron(III)-dihydrogen phosphate binding, and enable the binding between iron(III) and monohydrogen phosphate, which was hampered in hemin by the presence of the negatively charged propionate residues. Overall, this work provides a more complete speciation of immobilized iron porphyrins under acidic conditions than previously considered, showing the substitutional lability of the aqua ligand in the oxidized state of the iron center and the reluctance of its hydroxyl counterpart to anion exchange. Knowledge of these redox- and pH-dependent bindings with the buffer components is crucial for a rigorous quantification of the proton-coupled electron transfer and the electrocatalytic activity of iron porphyrins.

Partial T Cell-Depleted Peripheral Blood Stem Cell Transplantation from HLA-Identical Sibling Donors for Patients with Severe Aplastic Anemia.

We analyzed the outcomes of 26 consecutive patients with acquired severe aplastic anemia (SAA) undergoing peripheral blood stem cell transplantation (PBSCT) with partial ex vivo T cell depletion with a targeted T cell dose from HLA-identical sibling donors. The median patient age was 37 years (range, 3 to 63 years). Four patients with uncontrolled pneumonia at the time of transplantation died, on days +1, +2, +21, and +26. All evaluable patients engrafted, with a median time to neutrophil recovery of 11 days (range, 10 to 14 days) and a median time to platelet recovery of 19 days (range, 8 to 53 days). Two patients had transient grade I acute graft-versus-host disease (GVHD) with skin involvement, but no patients developed grade II-IV acute GVHD. Two patients had mild skin chronic GVHD, and 1 patient had moderate chronic GVHD with ocular involvement. No relapse was observed after a median follow-up of 114 months (range, 4 to 233 months). The overall cumulative incidence of TRM at 10 years was 19%, whereas it was 5% for those with a Karnofsky Performance Status (KPS) score >60 at the time of transplantation. Disease-free survival, overall survival, and GVHD and relapse-free survival at 10 years were 81%, 81%, and 80%, respectively, for all patients and 95%, 95%, and 90%, respectively, for patients with a KPS score >60 at transplantation. Our data indicate that PBSCT with partial ex vivo T cell-depleted targeted cell dose grafts from an HLA-identical sibling donor is a feasible, safe, and effective approach to reduce GVHD and cure patients with SAA.

RELINF: prospective epidemiological registry of lymphoid neoplasms in Spain. A project from the GELTAMO group.

Lymphomas are a large, heterogeneous group of neoplasms with well-defined characteristics, and this heterogeneity highlights the importance of epidemiological data. Knowledge of local epidemiology is essential to optimise resources, design clinical trials, and identify minority entities. Given there are few published epidemiological data on lymphoma in Spain, the Spanish Lymphoma and Autologous Bone Marrow Transplant Group created the RELINF project. The aim of this project is to determine the frequencies and distribution of lymphoid neoplasms in Spain and to analyse survival. We developed an online platform for the prospective collection of data on newly diagnosed cases of lymphoma in Spain between January 2014 and July 2018; 11,400 patients were registered. Diffuse large B cell lymphoma (DLBCL) and follicular lymphoma (FL) were the most frequent lymphomas in our series. Marginal B cell lymphoma frequency was higher than that reported in other studies, representing more than 11% of mature B cell lymphomas. Peripheral T cell lymphoma not otherwise specified (PTCL-NOS) was the most common subtype of T cell lymphoma, and NK/T cell lymphomas were more frequent than expected (5.4% of total). Hodgkin's lymphoma accounted for 12% of lymphoproliferative syndromes. Overall survival was greater than 90% at 2 years for indolent B cell lymphomas, and approximately 60% for DLBCL, somewhat lower than that previously reported. Survival was poor for PTCL-NOS and angioimmunoblastic T cell lymphoma, as expected; however, it was somewhat better than that in other studies for anaplastic large cell anaplastic lymphoma kinase lymphomas. This is the first prospective registry to report the frequencies, distribution, and survival of lymphomas in Spain. The frequencies and survival data we report here are globally consistent with that reported in other Western countries. These updated frequencies and survival statistics are necessary for developing appropriate management strategies for neoplasias in the Spanish population.

Interprotein Coupling Enhances the Electrocatalytic Efficiency of Tobacco Peroxidase Immobilized at a Graphite Electrode.

Covalent immobilization of enzymes at electrodes via amide bond formation is usually carried out by a two-step protocol, in which surface carboxylic groups are first activated with the corresponding cross-coupling reagents and then reacted with protein amine groups. Herein, it is shown that a modification of the above protocol, involving the simultaneous incubation of tobacco peroxidase and the pyrolytic graphite electrode with the cross-coupling reagents produces higher and more stable electrocatalytic currents than those obtained with either physically adsorbed enzymes or covalently immobilized enzymes according to the usual immobilization protocol. The remarkably improved electrocatalytic properties of the present peroxidase biosensor that operates in the 0.3 V ≤ E ≤ 0.8 V (vs SHE) potential range can be attributed to both an efficient electronic coupling between tobacco peroxidase and graphite and to the formation of intra- and intermolecular amide bonds that stabilize the protein structure and improve the percentage of anchoring groups that provide an adequate orientation for electron exchange with the electrode. The optimized tobacco peroxidase sensor exhibits a working concentration range of 10-900 µM, a sensitivity of 0.08 A M(-1) cm(-2) (RSD 0.05), a detection limit of 2 µM (RSD 0.09), and a good long-term stability, as long as it operates at low temperature. These parameter values are among the best reported so far for a peroxidase biosensor operating under simple direct electron transfer conditions.

Epstein-Barr virus-associated posttransplant lymphoproliferative disorder after allogeneic stem cell transplantation.

PURPOSE OF REVIEW: Epstein-Barr virus (EBV)-associated posttransplant lymphoproliferative disorder is an increasingly life-threatening complication after allogeneic stem cell transplantation with the use of more complex transplant procedures. RECENT FINDINGS: Reduced intensity conditioning regimens in combination with in-vivo or ex-vivo T-cell depletion are particularly important risk factors. Prospective monitoring of EBV viremia by real-time quantitative polymerase-chain reaction (PCR) should be performed after high-risk allogeneic stem cell transplantation. However, lack of standardization and concerns about sensitivity and low positive-predictive value challenge the interpretation of PCR monitoring. Preemptive treatment is feasible and can reduce EBV-related mortality but may lead to overtreatment in some patients. Readily available rituximab and methods of adoptive transfer of T-cells are valuable tools. Rituximab is probably the most attractive agent showing the most robust data in this setting. Rituximab seems to offer a good balance between efficacy and toxicity for the treatment of established EBV-associated posttransplant lymphoproliferative disorder. But most often there is a need to combine with adoptive immunotherapy with T-cells to maintain long-term disease control, with either simple unmanipulated donor lymphocyte infusion or more specific and complex adoptive EBV-specific cytotoxic T-cells. SUMMARY: EBV-associated posttransplant lymphoproliferative disorder can often be prevented or treated, especially in earlier stages. The specific role and timing of the different treatment strategies need to be defined.

Ibrutinib followed by ofatumumab consolidation in previously untreated patients with chronic lymphocytic leukemia (CLL): GELLC-7 trial from the Spanish group of CLL (GELLC).

Background: BTK inhibitors have been concurrently administered with anti-CD20 monoclonal antibodies (mAbs) in chronic lymphocytic leukemia (CLL). However, the optimal regimen for combining these two drugs remains pending. Methods: This multi-center phase 2 study aimed to analyze whether consolidation with ofatumumab improved the response in patients with CLL receiving front-line treatment with ibrutinib. Patients received 12 cycles of ibrutinib monotherapy. Those who achieved CR after this induction were maintained on ibrutinib. Conversely, those who did not attain CR continued with ibrutinib in addition to a consolidation, which involved 7 doses of ofatumumab. The primary objective was the complete response (CR) rate at cycle 20. This study is registered within the EU Clinical Trials Register (EudraCT 2016-004937-26). Findings: Between September 8, 2017, and May 21, 2018, 84 patients (median age, 69 years) were included. After completion of 12 cycles of ibrutinib (n = 80), 4 patients (5%) were in CR, 67 (84%) in partial response (PR), and 6 patients (7%) had a PR with lymphocytosis (PRL). After consolidation with ofatumumab, 20 patients improved the response from PR to CR and 6 patients with PRL obtained a PR. Seventy-one patients (85%) completed 20 cycles of treatment, with a CR rate of 24/71 (34%). According to the intention-to-treat analysis at cycle 20, the ORR was 69/84 (82.2%), with a CRR of 24/84 (28.6%). Progression-free survival and overall survival at 48-months were 89.9% (CI: 82.4-95.5) and 92.2% (CI: 85.3-97.1), respectively. Interpretation: These findings underscore the potential for a consolidation strategy in CLL, wherein the addition of a mAb in patients with low tumor burden might enhance the quality of the response. Funding: The study was funded by Janssen that also supplied ibrutinib, whereas ofatumumab was supplied by Novartis.

Ibrutinib and R-GemOx in patients with relapsed or refractory diffuse large B-cell lymphoma of non-GCB type: Phase II clinical trial of the Spanish GELTAMO group.

PURPOSE: This phase II clinical trial evaluated the combination of Ibrutinib with rituximab, gemcitabine and oxaliplatin (R-GemOx) in patients with non-germinal centre B-cell-like (non-GCB) diffuse large B-cell lymphoma (DLBCL). PATIENTS AND METHODS: The IBDCL trial (NCT02692248) included patients with histological diagnosis of non-GCB DLBCL with relapsed or refractory disease and non-candidates for stem cell transplantation. Patients received an induction treatment consisting of 6 or 8 cycles of R-GemOx at standard doses every 2 weeks, in combination with ibrutinib (560 mg daily), followed by a maintenance treatment with ibrutinib for a maximum of 2 years. The primary objective was to evaluate the overall response rate (ORR) after 4 cycles. RESULTS: Sixty-four patients were included, 72% of them refractory to the last regimen. The ORR and CR rate after the 4th cycle were 53% (95% confidence interval [CI], 41-65) and 34% (95% CI, 24-46), respectively. Twenty-four (37%) patients started maintenance and 7 (11%) completed the planned 2 years. After a median follow-up of 29.7 months (range: 0.4-48.6), the estimated 2-year PFS and OS were 18% (95% CI, 8 - 28) and 26% (95% CI, 14 - 37), respectively. The most common grade ≥3 treatment-related adverse events (TRAEs) were thrombocytopenia (44%), neutropenia (30%) and anemia (14%). Grade ≥3 infectious and cardiovascular TRAEs were reported in 6 (9%) and 1 (2%) patient, respectively. CONCLUSIONS: Ibrutinib in combination with R-GemOx, followed by ibrutinib maintenance, demonstrated encouraging antitumor activity with durable responses and a manageable toxicity in patients with non-GCB DLBCL.

Analytical expressions for proton transfer voltammetry: analogy to surface redox voltammetry with Frumkin interactions.

Theory for interfacial proton transfer voltammetry of a molecular film containing any acid/base loading has been developed under equilibrium conditions. Diagnostic criteria to disentangle the interplay between diffuse layer and ionization effects are outlined. Easy-to-use analytical expressions for the voltammetric features are derived for the particular case of an invariant diffuse layer effect, which turn out to be entirely analogous to those for a surface redox conversion with Frumkin interactions. It is demonstrated that, regardless of the electrolyte concentration, significant ionization of the external acid groups located nearby the diffuse layer is sufficient for the fulfillment of this relevant particular case. A strategy is outlined to determine the amount, the intrinsic pKa, and the burial depth of the voltammetrically active groups from the surface concentration dependence of the main voltammetric features. Self-assembled monolayers of 11-mercaptoundecanoic acid deposited on Au(111), containing higher amounts of buried carboxylic groups than previously reported, have been studied to assess more critically the influence of electrostatic effects on the ionization process. Preliminary evidence suggests that the protonation/deprotonation voltammetric wave involves physisorbed rather than chemisorbed thiol molecules. Application of the present theoretical approach to this system reveals that the voltammetrically active carboxylic groups are located close to the electrode surface and become more acidic upon increasing their surface concentration.

Accuracy and prognostic impact of FDG PET/CT and biopsy in bone marrow assessment of follicular lymphoma at diagnosis: A Nation-Wide cohort study.

BACKGOUND: In the workup of follicular lymphoma (FL), bone marrow biopsy (BMB) assessment is a key component of FLIPI and FLIPI2, the most widely used outcome scores. During the previous decade, several studies explored the role of FDG-PET/CT for detecting nodal and extranodal disease, with only one large study comparing both techniques. METHODS: The aim of our study was to evaluate the diagnostic accuracy and the prognostic impact of both procedures in a retrospective cohort of 299 FL patients with both tests performed at diagnosis. In order to avoid a collinearity bias, FLIPI2 was deconstructed in its founding parameters, and the bone marrow involvement (BMI) parameter separately included as: a positive BMB, a positive PET/CT, the combined "PET/CT and BMB positive" or "PET/CT or BMB positive". These variables were also confronted independently with the POD24 in 233 patients treated with intensive regimens. RESULTS: In the total cohort, bone marrow was involved in 124 and 60 patients by BMB and PET/CT, respectively. In terms of overall survival, age > 60 y.o. and the combined "PET/CT or BMB positive" achieved statistical independence as a prognostic factor. In patients treated with an intensive regimen, only the combined "PET/CT or BMB positive" added prognostic value for a shorter overall survival, when confronted with the POD24. CONCLUSION: Our results show that in FL both BMB and PET/CT should be considered at diagnosis, as their combined assessment provides independent prognostic value in the context of the most widely use clinical scores.

Better prognosis for patients with del(7q) than for patients with monosomy 7 in myelodysplastic syndrome.

BACKGROUND: Abnormalities involving chromosome 7 are frequent in myelodysplastic syndrome (MDS) and suggest a poor prognosis. METHODS: The authors examined the hypothesis that the clinical features and survival associated with isolated deletion (del) of part of the long arm of chromosome 7 (7q) in MDS are different from those associated with isolated monosomy 7 (complete loss of chromosome 7). In total, 133 patients with a diagnosis of de novo MDS (according to the World Health Organization [WHO] classification) and chromosome 7 abnormalities in the Spanish MDS Registry were evaluated retrospectively. Four karyotypic groups were identified: isolated del(7q) (n = 29), isolated monosomy 7 (n = 27), del(7q) with additional abnormalities (n = 24), and monosomy 7 with additional abnormalities (n = 53). RESULTS: Isolated del(7q) was more frequent in patients with less advanced MDS according to the WHO classification or the International Prognostic Scoring System. In addition, isolated del(7q) was associated with fewer blasts in bone marrow than other cytogenetics groups. Survival was significantly superior in patients with isolated del(7) than in those with isolated monosomy 7, del(7q) with additional abnormalities, or monosomy 7 with additional abnormalities. On multivariate analysis, age, the percentage of blasts in bone marrow, and other chromosome 7 abnormalities apart from isolated del(7q) were identified as independent risk factors for survival. CONCLUSIONS: The current results demonstrated that patients who had MDS with isolated del(7q) had some distinct clinical-pathologic characteristics as well as better survival than patients who had MDS with isolated monosomy 7.

Diffusional surface voltammetry as a probe of adsorption energetics.

Direct determination of the adsorption free energy for extremely low surface coverages (Henry limit) requires the use of a technique that must be highly sensitive to both the amount and the energetics of adsorbed molecules. Herein, we demonstrate that diffusional surface voltammetry (DSV), which embodies film and stripping voltammetries as two limiting cases, can be used to achieve this goal for electroactive adsorbates. To this end, a general analytical expression for the surface voltammetric peak potential of DSV is derived, which covers the full range of scan rates, bulk concentrations, and adsorptivity of the freely diffusing form of the redox couple, so that the surface redox conversion can be either equilibrated with or transport-isolated from the solution bulk. Strategies to get a quantitative insight into the energetics of electrosorption are outlined, and diagnostic criteria for their application are developed. In particular, it is demonstrated that DSV can be used in its stripping mode to determine group contributions to the adsorption free energy, avoiding possible interferences from intermolecular interactions or formation of oligomeric species. Application of this protocol to the reductive desorption of distinct homologous series of alkylthiolates adsorbed at mercury electrodes has allowed us to determine the contributions of the CH(n) groups (n = 0-3) to the free energy of adsorption of these molecules. These estimates are shown to correlate linearly with the corresponding group contributions to the octanol-water partition coefficient, revealing that adsorption of individual hydrocarbon groups at the mercury/solution interface scales with their hydrophobicity. Overall, the present work enlarges the capability of surface voltammetry to probe adsorption energetics down to the micromolar level, and it represents a first step toward the development of a unified treatment of stripping and film voltammetries.

Proton transfer voltammetry at electrodes modified with acid thiol monolayers.

By combining a description of the potential profile at electrodes coated with acid thiol monolayers with a quadratic relationship between activation energy and electrode potential, a rather simple expression for proton transfer voltammograms is derived. Our electrostatic analysis shows that proton transfer can only produce narrow voltammetric peaks when the immobilized acid groups lie close to the metal substrate. Quantitative fits of experimental voltammograms obtained with an Au(111) electrode modified with a 11-mercaptoundecanoic monolayer at pH 8.5 reveal that less than 1% of the carboxylic groups in the monolayer participate in the potential induced proton transfer process and that these groups lay close to the metal surface. A preliminary analysis of the kinetic parameters suggests that the interfacial electric field facilitates an intrinsically slow proton exchange between a proton donor and acceptor pair that are not in close contact with each other at the interface.

Electric field-induced functional changes in electrode-immobilized mutant species of human cytochrome c.

Post-translational modifications and naturally occurring mutations of cytochrome c have been recognized as a regulatory mechanism to control its biology. In this work, we investigate the effect of such in vivo chemical modifications of human cytochrome c on its redox properties in the adsorbed state onto an electrode. In particular, tyrosines 48 and 97 have been replaced by the non-canonical amino acid p-carboxymethyl-L-phenylalanine (pCMF), thus mimicking tyrosine phosphorylation. Additionally, tyrosine 48 has been replaced by a histidine producing the natural Y48H pathogenic mutant. Thermodynamics and kinetics of the interfacial electron transfer of wild-type cytochrome c and herein produced variants, adsorbed electrostatically under different local interfacial electric fields, were determined by means of variable temperature cyclic film voltammetry. It is shown that non-native cytochrome c variants immobilized under a low interfacial electric field display redox thermodynamics and kinetics similar to those of wild-type cytochrome c. However, upon increasing the strength of the electric field, the redox thermodynamics and kinetics of the modified proteins markedly differ from those of the wild-type species. The mutations promote stabilization of the oxidized form and a significant increase in the activation enthalpy values that can be ascribed to a subtle distortion of the heme cofactor and/or difference of the amino acid rearrangements rather than to a coarse protein structural change. Overall, these results point to a combined effect of the single point mutations at positions 48 and 97 and the strength of electrostatic binding on the regulatory mechanism of mitochondrial membrane activity, when acting as a redox shuttle protein.

Panel Sequencing for Clinically Oriented Variant Screening and Copy Number Detection in Chronic Lymphocytic Leukemia Patients.

According to current guidelines, in chronic lymphocytic leukemia (CLL), only the TP53 molecular status must be evaluated prior to every treatment's initiation. However, additional heterogeneous genetic events are known to confer a proliferative advantage to the tumor clone and are associated with progression and treatment failure in CLL patients. Here, we describe the implementation of a comprehensive targeted sequencing solution that is suitable for routine clinical practice and allows for the detection of the most common somatic single-nucleotide and copy number variants in genes relevant to CLL. We demonstrate that this cost-effective strategy achieves variant detection with high accuracy, specificity, and sensitivity. Furthermore, we identify somatic variants and copy number variations in genes with prognostic and/or predictive value, according to the most recent literature, and the tool provides evidence about subclonal events. This next-generation sequencing (NGS) capture-based target assay is an improvement on current approaches in defining molecular prognostic and/or predictive variables in CLL patients.

Accurate analytical expressions for stripping voltammetry in the Henry adsorption limit.

A strategy is developed to derive accurate analytical expressions for low-coverage cathodic stripping voltammetry. The procedure relies on the observation that diffusion affects the location of simulated voltammetric waves but not their shape, provided that physisorption of the analyte is negligible. As a proof of the generality of the proposed approach and having in mind the stripping of thiols, analytical solutions are derived for the cathodic stripping of monomers, dimers, and a mixture of monomers and dimers, whose reliability is proved by their comparison with numerically simulated voltammograms. Application to the deposition and reductive desorption of mercaptoacetic acid at a mercury electrode demonstrates that these approximate solutions can be used to get insights into the interfacial organization of incipient films. For this particular system, a transition from monomeric to dimeric behavior is identified upon increasing the thiol surface concentration. Further generalization of the proposed methodology is achieved by deriving an approximate analytical solution for thin-layer anodic stripping voltammetry, which is satisfactorily compared to the existing summation series solution.

Chemical reactivity and electrochemistry of metal-metal-bonded zincocenes.

Attempts to prepare mixed-ligand zinc-zinc-bonded compounds that contain bulky C(5)Me(5) and terphenyl groups, [Zn(2)(C(5)Me(5))(Ar')], lead to disproportionation. The resulting half-sandwich Zn(II) complexes [(η(5)-C(5)Me(5))ZnAr'] (Ar' = 2,6-(2,6-(i)Pr(2)C(6)H(3))(2)-C(6)H(3), 2; 2,6-(2,6-Me(2)C(6)H(3))(2)-C(6)H(3), 3) can also be obtained from the reaction of [Zn(C(5)Me(5))(2)] with the corresponding LiAr'. In the presence of pyr-py (4-pyrrolidinopyridine) or DBU (1,8-diazabicyclo[5.4.0]undec-7-ene), [Zn(2)(η(5)-C(5)Me(5))(2)] reacts with C(5)Me(5)OH to afford the tetrametallic complexes [Zn(2)(η(5)-C(5)Me(5))L(µ-OC(5)Me(5))](2) (L = pyr-py, 6; DBU, 8), respectively. The bulkier terphenyloxide Ar(Mes)O(-) group (Ar(Mes) = 2,6-(2,4,6-Me(3)C(6)H(2))(2)-C(6)H(3)) gives instead the dimetallic compound [Zn(2)(η(5)-C(5)Me(5))(OAr(Mes))(pyr-py)(2)], 7, that features a terminal Zn-OAr(Mes) bond. DFT calculations on models of 6-8 and also on the Zn-Zn-bonded complexes [Zn(2)(η(5)-C(5)H(5))(OC(5)H(5))(py)(2)] and [(η(5)-C(5)H(5))ZnZn(py)(3)](+) have been performed and reveal the nonsymmetric nature of the Zn-Zn bond with lower charge and higher participation of the s orbital of the zinc atom coordinated to the cyclopentadienyl ligand with respect to the metal within the pseudo-ZnL(3) fragment. Cyclic voltammetric studies on [Zn(2)(η(5)-C(5)Me(5))(2)] have been also carried out and the results compared with the behavior of [Zn(C(5)Me(5))(2)] and related magnesium and calcium metallocenes.

Structural and functional insights into lysine acetylation of cytochrome c using mimetic point mutants.

Post-translational modifications frequently modulate protein functions. Lysine acetylation in particular plays a key role in interactions between respiratory cytochrome c and its metabolic partners. To date, in vivo acetylation of lysines at positions 8 and 53 has specifically been identified in mammalian cytochrome c, but little is known about the structural basis of acetylation-induced functional changes. Here, we independently replaced these two residues in recombinant human cytochrome c with glutamine to mimic lysine acetylation and then characterized the structure and function of the resulting K8Q and K53Q mutants. We found that the physicochemical features were mostly unchanged in the two acetyl-mimetic mutants, but their thermal stability was significantly altered. NMR chemical shift perturbations of the backbone amide resonances revealed local structural changes, and the thermodynamics and kinetics of electron transfer in mutants immobilized on gold electrodes showed an increase in both protein dynamics and solvent involvement in the redox process. We also observed that the K8Q (but not the K53Q) mutation slightly increased the binding affinity of cytochrome c to its physiological electron donor, cytochrome c1 -which is a component of mitochondrial complex III, or cytochrome bc1 -thus suggesting that Lys8 (but not Lys53) is located in the interaction area. Finally, the K8Q and K53Q mutants exhibited reduced efficiency as electron donors to complex IV, or cytochrome c oxidase.