Topography of human cytochrome b5/cytochrome b5 reductase interacting domain and redox alterations upon complex formation.

Cytochrome b5 is the main electron acceptor of cytochrome b5 reductase. The interacting domain between both human proteins has been unidentified up to date and very little is known about its redox properties modulation upon complex formation. In this article, we characterized the protein/protein interacting interface by solution NMR and molecular docking. In addition, upon complex formation, we measured an increase of cytochrome b5 reductase flavin autofluorescence that was dependent upon the presence of cytochrome b5. Data analysis of these results allowed us to calculate a dissociation constant value between proteins of 0.5±0.1µM and a 1:1 stoichiometry for the complex formation. In addition, a 30mV negative shift of cytochrome b5 reductase redox potential in presence of cytochrome b5 was also measured. These experiments suggest that the FAD group of cytochrome b5 reductase increase its solvent exposition upon complex formation promoting an efficient electron transfer between the proteins.

Electron transfer and docking between cytochrome cd1 nitrite reductase and different redox partners - A comparative study.

Cytochrome cd1 nitrite reductases (cd1NiRs) catalyze the reduction of nitrite to nitric oxide in denitrifying bacteria, such as Marinobacter hydrocarbonoclasticus. Previous work demonstrated that the enzymatic activity depends on a structural pre-activation triggered by the entry of electrons through the electron transfer (ET) domain, which houses a heme c center. The catalytic activity of M. hydrocarbonoclasticus cd1NiR (Mhcd1NiR) was tested by mediated electrochemistry, using small ET proteins and chemical redox mediators. The rate of enzymatic reaction depends on the nature of the redox partner, with cytochrome (cyt) c552 providing the highest value. In situations where cyt c552 is replaced by either a biological (cyt c from horse heart) or a chemical mediator the catalytic response was only observed at very low scan rates, suggesting that the intermolecular ET rate is much slower. Molecular docking simulations with the 3D model structure of Mhcd1NiR and cyt c552 or cyt c showed that hydrophobic interactions favor the formation of complexes where the heme c domain of the enzyme is the principal docking site. However, only in the case of cyt c552 the preferential areas of contact and Fe-Fe distances between heme c groups of the redox partners allow establishing competent ET pathways. The coupling of the enzyme with chemical redox mediators was also found not to be energetically favorable. These results indicate that although low activity functional complexes can be formed between Mhcd1NiR and different types of redox mediators, efficient ET is only observed with the putative physiological electron donor cyt c552.

Insights into the Molybdenum/Copper Heterometallic Cluster Assembly in the Orange Protein: Probing Intermolecular Interactions with an Artificial Metal-Binding ATCUN Tag.

Orange protein (ORP) is a small bacterial protein, of unknown function, that contains a unique molybdenum/copper heterometallic cluster, [S2MoVIS2CuIS2MoVIS2]3- (Mo/Cu), non-covalently bound. The native cluster can be reconstituted in a protein-assisted mode by the addition of CuII plus tetrathiomolybdate to apo-ORP under controlled conditions. In the work described herein, we artificially inserted the ATCUN ("amino terminus Cu and Ni") motif in the Desulfovibrio gigas ORP (Ala1Ser2His3 followed by the native amino acid residues; modified protein abbreviated as ORP*) to increase our understanding of the Mo/Cu cluster assembly in ORP. The apo-ORP* binds CuII in a 1:1 ratio to yield CuII-ORP*, as clearly demonstrated by EPR (g||,⊥ = 2.183, 2.042 and ACu||,⊥ = 207 × 10-4 cm-1, 19 × 10-4 cm-1) and UV-visible spectroscopies (typical d-d transition bands at 520 nm, ε = 90 M-1 cm-1). The 1H NMR spectrum shows that His3 and His53 are significantly affected upon the addition of the CuII. The X-ray structure shows that these two residues are very far apart (Cα-Cα ≈ 27.9 Å), leading us to suggest that the metal-induced NMR perturbations are due to the interaction of two protein molecules with a single metal ion. Docking analysis supports the metal-mediated dimer formation. The subsequent tetrathiomolybdate binding, to yield the native Mo/Cu cluster, occurs only upon addition of dithiothreitol, as shown by UV-visible and NMR spectroscopies. Additionally, 1H NMR of AgI-ORP* (AgI used as a surrogate of CuI) showed that AgI strongly binds to a native methionine sulfur atom rather than to the ATCUN site, suggesting that CuII and CuI have two different binding sites in ORP*. A detailed mechanism for the formation of the Mo/Cu cluster is discussed, suggesting that CuII is reduced to CuI and transferred from the ATCUN motif to the methionine site; finally, CuI is transferred to the cluster-binding region, upon the interaction of two protein molecules. This result may suggest that copper trafficking is triggered by redox-dependent coordination properties of copper in a trafficking pathway.

Predicting Protein-Protein Interactions Using BiGGER: Case Studies.

The importance of understanding interactomes makes preeminent the study of protein interactions and protein complexes. Traditionally, protein interactions have been elucidated by experimental methods or, with lower impact, by simulation with protein docking algorithms. This article describes features and applications of the BiGGER docking algorithm, which stands at the interface of these two approaches. BiGGER is a user-friendly docking algorithm that was specifically designed to incorporate experimental data at different stages of the simulation, to either guide the search for correct structures or help evaluate the results, in order to combine the reliability of hard data with the convenience of simulations. Herein, the applications of BiGGER are described by illustrative applications divided in three Case Studies: (Case Study A) in which no specific contact data is available; (Case Study B) when different experimental data (e.g., site-directed mutagenesis, properties of the complex, NMR chemical shift perturbation mapping, electron tunneling) on one of the partners is available; and (Case Study C) when experimental data are available for both interacting surfaces, which are used during the search and/or evaluation stage of the docking. This algorithm has been extensively used, evidencing its usefulness in a wide range of different biological research fields.

A unified in vitro evaluation for apatite-forming ability of bioactive glasses and their variants.

The aim of this study was to propose and validate a new unified method for testing dissolution rates of bioactive glasses and their variants, and the formation of calcium phosphate layer formation on their surface, which is an indicator of bioactivity. At present, comparison in the literature is difficult as many groups use different testing protocols. An ISO standard covers the use of simulated body fluid on standard shape materials but it does not take into account that bioactive glasses can have very different specific surface areas, as for glass powders. Validation of the proposed modified test was through round robin testing and comparison to the ISO standard where appropriate. The proposed test uses fixed mass per solution volume ratio and agitated solution. The round robin study showed differences in hydroxyapatite nucleation on glasses of different composition and between glasses of the same composition but different particle size. The results were reproducible between research facilities. Researchers should use this method when testing new glasses, or their variants, to enable comparison between the literature in the future.

Superoxide reductase: different interaction modes with its two redox partners.

Anaerobic organisms have molecular systems to detoxify reactive oxygen species when transiently exposed to oxygen. One of these systems is superoxide reductase, which reduces O2 (.-) to H2 O2 without production of molecular oxygen. In order to complete the reduction of superoxide anion, superoxide reductase requires an electron, delivered by its redox partners, which in Desulfovibrio gigas are rubredoxin and/or desulforedoxin. In this work, we characterized the interaction of Desulfovibrio gigas superoxide reductase with both electron donors by using steady-state kinetics, 2D NMR titrations, and backbone relaxation measurements. The rubredoxin surface involved in the electron transfer complex with superoxide reductase comprises the solvent-exposed hydrophobic residues in the vicinity of its metal center (Cys9, Gly10, Cys42, Gly43, and Ala44), and a Kd of 3 µM at 59 mM ionic strength was estimated by NMR. The ionic strength dependence of superoxide-mediated rubredoxin oxidation by superoxide reductase has a maximum kapp of (37 ± 12) min(-1) at 157 mM. Relative to the electron donor desulforedoxin, its complex with superoxide reductase was not detected by chemical shift perturbation, though this protein is able to transfer electrons to superoxide reductase with a maximum kapp of (31 ± 7) min(-1) at an ionic strength of 57 mM. Competition experiments using steady-state kinetics and NMR spectroscopy (backbone relaxation measurements and use of a paramagnetic relaxation enhancement probe) with Fe-desulforedoxin in the presence of (15) N-Zn-rubredoxin showed that these two electron donors compete for the same site on the enzyme surface, as shown in the model structure of the complex generated by using restrained molecular docking calculations. These combined strategies indicate that the two small electron donors bind in different manners, with the desulforedoxin complex being a short lived electron transfer complex or more dynamic, with many equivalent kinetically competent orientations.

Risk of Bias in Randomized Clinical Trials Comparing Transcatheter and Surgical Aortic Valve Replacement: A Systematic Review and Meta-analysis.

Importance: Recent European Society of Cardiology/European Association for Cardio-Thoracic Surgery (ESC/EACTS) guidelines highlighted some concerns about the randomized clinical trials (RCTs) comparing transcatheter aortic valve implantation (TAVI) and surgical aortic valve replacement (SAVR) for aortic stenosis. Quantification of these biases has not been previously performed. Objective: To assess whether randomization protects RCTs comparing TAVI and SAVR from biases other than nonrandom allocation. Data Sources: A systematic review of the literature between January 1, 2007, and June 6, 2022, on MEDLINE, Embase, and Cochrane Central Register of Controlled Trials was performed. Specialist websites were also checked for unpublished data. Study Selection: The study included RCTs with random allocation to TAVI or SAVR with a maximum 5-year follow-up. Data Extraction and Synthesis: Data extraction was performed by 2 independent investigators following the PRISMA guidelines. A random-effects meta-analysis was used for quantifying pooled rates and differential rates between treatments of deviation from random assigned treatment (DAT), loss to follow-up, and receipt of additional treatments. Main Outcomes and Measures: The primary outcomes were the proportion of DAT, loss to follow-up, and patients who were provided additional treatments and myocardial revascularization, together with their ratio between treatments. The measures were the pooled overall proportion of the primary outcomes and the risk ratio (RR) in the TAVI vs SAVR groups. Results: The search identified 8 eligible trials including 8849 participants randomly assigned to undergo TAVI (n = 4458) or SAVR (n = 4391). The pooled proportion of DAT among the sample was 4.2% (95% CI, 3.0%-5.6%), favoring TAVI (pooled RR vs SAVR, 0.16; 95% CI, 0.08-0.36; P < .001). The pooled proportion of loss to follow-up was 4.8% (95% CI, 2.7%-7.3%). Meta-regression showed a significant association between the proportion of participants lost to follow-up and follow-up time (slope, 0.042; 95% CI, 0.017-0.066; P < .001). There was an imbalance of loss to follow-up favoring TAVI (RR, 0.39; 95% CI, 0.28-0.55; P < .001). The pooled proportion of patients who had additional procedures was 10.4% (95% CI, 4.4%-18.5%): 4.6% (95% CI, 1.5%-9.3%) in the TAVI group and 16.5% (95% CI, 7.5%-28.1%) in the SAVR group (RR, 0.27; 95% CI, 0.15-0.50; P < .001). The imbalance between groups also favored TAVI for additional myocardial revascularization (RR, 0.40; 95% CI, 0.24-0.68; P < .001). Conclusions and Relevance: This study suggests that, in RCTs comparing TAVI vs SAVR, there are substantial proportions of DAT, loss to follow-up, and additional procedures together with systematic selective imbalance in the same direction characterized by significantly lower proportions of patients undergoing TAVI that might affect internal validity.

Perspectives in Training and Professional Practice of Cardiac Surgery in Latin America.

INTRODUCTION: There is a lack of information about cardiac surgery training and professional practice in Latin American (LATAM) countries. This study is the first comparative analysis of cardiac surgical training and professional practice across LATAM and provides the fundamentals for future academic projects of the Latin American Association of Cardiac and Endovascular Surgery (LACES). METHODS: International survey-based comparative analysis of the training and professional practice of cardiac surgeons across LATAM. Trainees (residents/fellows) and staf (graduated) surgeons from LATAM countries were included. RESULTS: A total of 289 respondents (staf surgeons N=221 [76.5%]; residents/fellows N=68 [23.5%]) from 18 different countries participated in the survey. Most surgeons (N=92 [45.3%]) reported being unsatisfied with their salaries. Most respondents (N=181 [62.6%]) stated that it was difficult to obtain a leadership position, and 149 (73.8%) stated that it was difficult to find a job after completing training. Only half of the trainee respondents (N=32 [47.1%]) reported that their program had all resident spots occupied. Only 22.1% (N=15) of residents/fellows were satisfied with their training programs. The majority (N=205 [70.9%]) of respondents would choose cardiac surgery as their specialty again. Most surgeons (N=129 [63.9%]) and residents/fellows (N=52 [76.5%]) indicated that the establishment of a LATAM cardiac surgery board examination would be beneficial. CONCLUSION: Modernization and standardization of training, as well as greater access to opportunities, may be required in LATAM to increase professional satisfaction of cardiac surgeons and to reduce disparities in the specialty. Such changes may enhance the regional response to the dynamic challenges in the feld.

Randomized evidence for reduction of perioperative mortality.

OBJECTIVE: With more than 220 million major surgical procedures performed annually, perioperative interventions leading to even minor mortality reductions would save thousands of lives per year. This international consensus conference aimed to identify all nonsurgical interventions that increase or reduce perioperative mortality as suggested by randomized evidence. DESIGN AND SETTING: A web-based international consensus conference. PARTICIPANTS: More than 1,000 physicians from 77 countries participated in this web-based consensus conference. INTERVENTIONS: Systematic literature searches (MEDLINE/PubMed, June 8, 2011) were used to identify the papers with a statistically significant effect on mortality together with contacts with experts. Interventions were considered eligible for evaluation if they (1) were published in peer-reviewed journals, (2) dealt with a nonsurgical intervention (drug/technique/strategy) in adult patients undergoing surgery, and (3) provided a statistically significant mortality increase or reduction as suggested by a randomized trial or meta-analysis of randomized trials. MEASUREMENTS AND MAIN RESULTS: Fourteen interventions that might change perioperative mortality in adult surgery were identified. Interventions that might reduce mortality include chlorhexidine oral rinse, clonidine, insulin, intra-aortic balloon pump, leukodepletion, levosimendan, neuraxial anesthesia, noninvasive respiratory support, hemodynamic optimization, oxygen, selective decontamination of the digestive tract, and volatile anesthetics. In contrast, aprotinin and extended-release metoprolol might increase mortality. CONCLUSIONS: Future research and health care funding should be directed toward studying and evaluating these interventions.

Gd(III) chelates as NMR probes of protein-protein interactions. Case study: rubredoxin and cytochrome c3.

Two cyclen-derived Gd probes, [Gd-DOTAM](3+) and [Gd-DOTP](5-) (DOTAM = 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetamide; DOTP = 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetrakis(methylenephosphonate)), were assessed as paramagnetic relaxation enhancement (PRE)-inducing probes for characterization of protein-protein interactions. Two proteins, Desulfovibrio gigas rubredoxin and Desulfovibrio gigas cytochrome c(3), were used as model partners. In a (1)H NMR titration it was shown that [Gd-DOTP](5-) binds to cytochrome c(3) near heme IV, causing pronounced PREs, characterized by line width broadenings of the heme methyl resonances at ratios as low as 0.08. A K(d) of 23 ± 1 µM was calculated based on chemical shift perturbation of selected heme methyl resonances belonging to three different heme groups, caused by allosteric effects upon [Gd-DOTP](5-) binding to cytochrome c(3) at a molar ratio of 2. The other probe, [Gd-DOTAM](3+), caused PREs on a well-defined patch near the metal center of rubredoxin (especially the patch constituted by residues D19-G23 and W37-S45, which broaden beyond detection). This effect was partially reversed for some resonances (C6-Y11, in particular) when cytochrome c(3) was added to this system. Both probes were successful in causing reversible PREs at the partner binding site, thus showing to be good probes to identify partners' binding sites and since the interaction is reversible to structurally characterize protein complexes by better defining the complex interface.

Quality of Life after 114 months of follow-up following geometric reconstruction of the left ventricle by endoventriculoplasty with septal exclusion.

BACKGROUND: The purpose of this study was to present the surgical experience of the Institute of Cardiovascular Surgery of West of Paraná (ICCOP) with respect to the treatment of left ventricle aneurysms by endoventriculoplasty with septal exclusion (EVSE) and to evaluate the quality of life of these patients after a 114-month follow-up. METHODS: Between April 1999 and April 2006, 28 patients underwent EVSE. Preoperative, transoperative, and late postoperative clinical and echocardiographic variables were analyzed retrospectively. In addition, latepostoperative quality of life was evaluated with questionnaire SF-36 (Brazilian version). The mean age (+/-SD) of the group was 59.0 +/- 9.5 years, and 23 of the patients were male. Seventeen patients were in New York Heart Association functional class IV, and the mean preoperative EuroSCORE was 8.2 +/- 2.3. The mean preoperative values for the ejection fraction (EF) and the end-systolic and end-diastolic left ventricular volumes were 32.3% +/- 9.2%, 113.9 +/- 36.0 mL, and 179.2 +/- 48.4 mL, respectively. RESULTS: The in-hospital mortality rate was 14.3%, with the major causes of morbidity being low cardiac output syndrome and arrhythmias. The mean follow-up period was 5.9 +/- 3.4 years. The left ventricular EF and the aortic cross-clamping time were the significant factors for hospital and late mortality (P = .0222, and P = .0123, respectively). The actuarial survival curve showed survival rates of 82.1 +/- 7.2%, and 54.7 +/- 22.9%, before and after 107 months of follow-up. The overall score for the quality of life showed an improvement. CONCLUSION: EVSE surgery is an effective option for treating this group of patients, with improvement noted in left ventricular function and in the patients' quality of life, despite the high in-hospital mortality.

Global perspectives on cardiothoracic, cardiovascular, and cardiac surgical training.

OBJECTIVE: Various methods for cardiothoracic, cardiovascular, and cardiac surgical training exist across the globe, with the common goal of producing safe, independent surgeons. A comparative analysis of international training paradigms has not been undertaken, and our goal in doing so was to offer insights into how to best prepare future trainees and ensure the health of our specialty. METHODS: We performed a comparative analysis of available publications offering detailed descriptions of various cardiothoracic, cardiovascular, and cardiac surgical training paradigms. Corresponding authors from previous publications and other international collaborators were also reached directly for further data acquisition. RESULTS: We report various approaches to common challenges surrounding (1) selection of trainees and plans for the future surgical workforce; (2) trainee assessments and certification of competency before independent practice; and (3) challenges related to a changing practice landscape. CONCLUSIONS: Cardiothoracic surgery remains a dynamic and rewarding specialty. Current and future trainees face several challenges that transcend national borders. To foster collaboration and adoption of best practices, we highlight international strengths and weaknesses of various nations in terms of workforce selection, trainee operative experience and assessment, board certification, and preparation for future changes anticipated in cardiothoracic surgery.

Endovascular Treatment of the Ascending Aorta: is this the Last Frontier in Aortic Surgery?

Regardless the successful treatment of the descending aorta with endovascular prosthesis, for the ascending aorta segment, because of several anatomic and physiologic issues, this technique has been considered an alternative only for high-risk or inoperable patients. Despite restricted indications, hundreds of treatments have been performed worldwide, demonstrating its safety and reproducibility if it is done in high-quality centers. Therefore, understanding patients' selection criteria and technique limitations are critical to its application.

Impact of the COVID-19 Outbreak on Coronary Artery Bypass Grafting in Brazil

Abstract Background The COVID-19 pandemic has disrupted the routine of emergency centers around the world, including in Brazil, where the crisis has affected the volume of major cardiac surgeries such as coronary artery bypass grafting. Objective To analyze the impact of the COVID-19 pandemic on the number of surgical procedures for coronary artery bypass grafting in Brazil. Methods An ecological, cross-sectional, quantitative, and descriptive study was conducted. Data for the period from July 2018 to June 2019 and from July 2020 to June 2021 were collected from SIHSUS using DATASUS/Tabwin. Results A global reduction of 26.58% was observed in the analyzed population, with on-pump coronary artery bypass grafting decreasing by 28.10%, and off-pump coronary artery bypass grafting reduced by only 10.31%. Conclusion During the pandemic, there was a 26.58% reduction in the number of surgical procedures for myocardial revascularization in Brazil.

Perspectives in Training and Professional Practice of Cardiac Surgery in Latin America

ABSTRACT Introduction: There is a lack of information about cardiac surgery training and professional practice in Latin American (LATAM) countries. This study is the first comparative analysis of cardiac surgical training and professional practice across LATAM and provides the fundamentals for future academic projects of the Latin American Association of Cardiac and Endovascular Surgery (LACES). Methods: International survey-based comparative analysis of the training and professional practice of cardiac surgeons across LATAM. Trainees (residents/fellows) and staf (graduated) surgeons from LATAM countries were included. Results: A total of 289 respondents (staf surgeons N=221 [76.5%]; residents/fellows N=68 [23.5%]) from 18 different countries participated in the survey. Most surgeons (N=92 [45.3%]) reported being unsatisfied with their salaries. Most respondents (N=181 [62.6%]) stated that it was difficult to obtain a leadership position, and 149 (73.8%) stated that it was difficult to find a job after completing training. Only half of the trainee respondents (N=32 [47.1%]) reported that their program had all resident spots occupied. Only 22.1% (N=15) of residents/fellows were satisfied with their training programs. The majority (N=205 [70.9%]) of respondents would choose cardiac surgery as their specialty again. Most surgeons (N=129 [63.9%]) and residents/fellows (N=52 [76.5%]) indicated that the establishment of a LATAM cardiac surgery board examination would be beneficial. Conclusion: Modernization and standardization of training, as well as greater access to opportunities, may be required in LATAM to increase professional satisfaction of cardiac surgeons and to reduce disparities in the specialty. Such changes may enhance the regional response to the dynamic challenges in the feld.

Ge-O coordination in cesium germanate glasses.

Neutron diffraction data with high real-space resolution are reported for an extensive series of cesium germanate glasses with 2, 5, 10, 15, 18, 21, 25, and 30 mol % Cs(2)O, and also for pure GeO(2) in its vitreous, quartz, and rutile forms. The results for pure GeO(2) show that neutron diffraction can clearly identify an increase in the Ge-O coordination number above the tetrahedral value of four. The results for cesium germanate glasses give strong evidence that the Ge-O coordination number rises to a maximum of 4.36 +/- 0.03 for 18 mol % Cs(2)O and then declines. This behavior may be associated with the germanate anomaly in the thermophysical properties. A model is developed for the composition-dependence of the Ge-O coordination number, and according to this model the rise in the coordination number involves the formation of mostly GeO(5) units, rather than GeO(6) units. Our results also show that the low alkali anomaly is a longer range phenomenon, and is not associated with a preference for the formation of nonbridging oxygens for very low alkali oxide content.

Sol-Gel Derived Active Material for Yb Thin-Disk Lasers.

A ytterbium doped active material for thin-disk laser was developed based on aluminosilicate and phosphosilicate glass matrices containing up to 30 mol% YbO1.5. Thick films and bulk samples were prepared by sol-gel processing. The structural nature of the base material was assessed by X-ray diffraction and Raman spectroscopy and the film morphology was evidenced by scanning electron microscopy. The photoluminescence (PL) properties of different compositions, including emission spectra and lifetimes, were also studied. Er3+ was used as an internal reference to compare the intensities of the Yb3+ PL peaks at ~ 1020 nm. The Yb3+ PL lifetimes were found to vary between 1.0 and 0.5 ms when the Yb concentration increased from 3 to 30 mol%. Based on a figure of merit, the best active material selected was the aluminosilicate glass composition 71 SiO2-14 AlO1.5-15 YbO1.5 (in mol%). An active disk, ~ 36 µm thick, consisting of a Bragg mirror, an aluminosilicate layer doped with 15 mol% Yb and an anti-reflective coating, was fabricated.

Insights into the recognition and electron transfer steps in nitric oxide reductase from Marinobacter hydrocarbonoclasticus.

Marinobacter hydrocarbonoclasticus nitric oxide reductase, cNOR, is an integral membrane protein composed of two subunits with different roles, NorC (electron transfer) and NorB (catalytic) that receives electrons from the soluble cytochrome c552 and reduces nitric oxide to nitrous oxide in the denitrification pathway. The solvent-exposed domain of NorC, harboring a c-type heme was heterologously produced, along with its physiological electron donor, cytochrome c552. These two proteins were spectroscopically characterized and shown to be similar to the native proteins, both being low-spin and Met-His coordinated, with the soluble domain of NorC presenting some additional features of a high-spin heme, which is consistent with the higher solvent accessibility of its heme and weaker coordination of the methionine axial ligand. The electron transfer complex between the two proteins has a 1:1 stoichiometry, and an upper limit for the dissociation constant was estimated by 1H NMR titration to be 1.2±0.4µM. Electrochemical techniques were used to characterize the interaction between the proteins, and a model structure of the complex was obtained by molecular docking. The electrochemical observations point to the modulation of the NorC reduction potential by the presence of NorB, tuning its ability to receive electrons from cytochrome c552.