Protector Role of Cx30.2 in Pancreatic ß-Cell against Glucotoxicity-Induced Apoptosis.

Glucotoxicity may exert its deleterious effects on pancreatic ß-cell function via a myriad of mechanisms, leading to impaired insulin secretion and, eventually, type 2 diabetes. ß-cell communication requires gap junction channels to be present among these cells. Gap junctions are constituted by transmembrane proteins of the connexins (Cxs) family. Two Cx genes have been identified in ß cells, Cx36 and Cx30.2. We have found evidence that the glucose concentration on its own is sufficient to regulate Cx30.2 gene expression in mouse islets. In this work, we examine the involvement of the Cx30.2 protein in the survival of ß cells (RIN-m5F). METHODS: RIN-m5F cells were cultured in 5 mM D-glucose (normal) or 30 mM D-glucose (high glucose) for 24 h. Cx30.2 siRNAs was used to downregulate Cx30.2 expression. Apoptosis was measured by means of TUNEL, an annexin V staining method, and the cleaved form of the caspase-3 protein was determined using Western blot. RESULTS: High glucose did not induce apoptosis in RIN-m5F ß cells after 24 h; interestingly, high glucose increased the Cx30.2 total protein levels. Moreover, this work found that the downregulation of Cx30.2 expression in high glucose promoted apoptosis in RIN-m5F cells. CONCLUSION: The data suggest that the upregulation of Cx30.2 protects ß cells from hyperglycemia-induced apoptosis. Furthermore, Cx30.2 may be a promising avenue of therapeutic investigation for the treatment of glucose metabolic disorders.

Solvent constraints for biopolymer folding and evolution in extraterrestrial environments.

We propose that spontaneous folding and molecular evolution of biopolymers are two universal aspects that must concur for life to happen. These aspects are fundamentally related to the chemical composition of biopolymers and crucially depend on the solvent in which they are embedded. We show that molecular information theory and energy landscape theory allow us to explore the limits that solvents impose on biopolymer existence. We consider 54 solvents, including water, alcohols, hydrocarbons, halogenated solvents, aromatic solvents, and low molecular weight substances made up of elements abundant in the universe, which may potentially take part in alternative biochemistries. We find that along with water, there are many solvents for which the liquid regime is compatible with biopolymer folding and evolution. We present a ranking of the solvents in terms of biopolymer compatibility. Many of these solvents have been found in molecular clouds or may be expected to occur in extrasolar planets.

The distinct cell physiology of Bradyrhizobium at the population and cellular level.

The α-Proteobacteria belonging to Bradyrhizobium genus are microorganisms of extreme slow growth. Despite their extended use as inoculants in soybean production, their physiology remains poorly characterized. In this work, we produced quantitative data on four different isolates: B. diazoefficens USDA110, B. diazoefficiens USDA122, B. japonicum E109 and B. japonicum USDA6 which are representative of specific genomic profiles. Notably, we found conserved physiological traits conserved in all the studied isolates: (i) the lag and initial exponential growth phases display cell aggregation; (ii) the increase in specific nutrient concentration such as yeast extract and gluconate hinders growth; (iii) cell size does not correlate with culture age; and (iv) cell cycle presents polar growth. Meanwhile, fitness, cell size and in vitro growth widely vary across isolates correlating to ribosomal RNA operon number. In summary, this study provides novel empirical data that enriches the comprehension of the Bradyrhizobium (slow) growth dynamics and cell cycle.

Structure-Based Optimization of Carbendazim-Derived Tubulin Polymerization Inhibitors through Alchemical Free Energy Calculations.

Carbendazim derivatives, commonly used as antiparasitic drugs, have shown potential as anticancer agents due to their ability to induce cell cycle arrest and apoptosis in human cancer cells by inhibiting tubulin polymerization. Crystallographic structures of α/ß-tubulin multimers complexed with nocodazole and mebendazole, two carbendazim derivatives with potent anticancer activity, highlighted the possibility of designing compounds that occupy both benzimidazole- and colchicine-binding sites. In addition, previous studies have demonstrated that the incorporation of a phenoxy group at position 5/6 of carbendazim increases the antiproliferative activity in cancer cell lines. Despite the significant progress made in identifying new tubulin-targeting anticancer compounds, further modifications are needed to enhance their potency and safety. In this study, we explored the impact of modifying the phenoxy substitution pattern on antiproliferative activity. Alchemical free energy calculations were used to predict the binding free energy difference upon ligand modification and define the most viable path for structure optimization. Based on these calculations, seven compounds were synthesized and evaluated against lung and colon cancer cell lines. Our results showed that compound 5a, which incorporates an α-naphthyloxy substitution, exhibits the highest antiproliferative activity against both cancer lines (SK-LU-1 and SW620, IC50 < 100 nM) and induces morphological changes in the cells associated with mitotic arrest and mitotic catastrophe. Nevertheless, the tubulin polymerization assay showed that 5a has a lower inhibitory potency than nocodazole. Molecular dynamics simulations suggested that this low antitubulin activity could be associated with the loss of the key H-bond interaction with V236. This study provides insights into the design of novel carbendazim derivatives with anticancer activity.

Metabolites from the Andean paramo lichen Cladonia cf. didyma and their effect as photoprotective and antioxidant agents.

5α,8α-peroxyergosteryl divaricatinate (1) is isolated for the first time from acetone extract of the thallus of Cladonia cf. didyma together with condidymic (2), isodidymic (3) and barbatic (4) acids. Their UVB/UVA photoprotective and antioxidant activities were determined along with their cyto- and DNA-protecting actions against OH• damage. Compound 1 showed high UVA, cyto- (%cell viability ca. 82 at 15 µM vs 71 for OH•) and DNA (%DNA-integrity ca. 74 at 100 µM vs 22 for OH•) protecting properties. Compounds 2 and 3 exhibited high UVB (SPF ca. 40) and antioxidant activities (free radical scavenging potency EC50 = 0.6694 and 1.700 mol compound/mol DPPH•; ferric reducing power 0.392 and 0.546, at 500 ppm and inhibited lipid peroxidation); protecting cells (%cell viability ca. 76 at 15 µM) and DNA (%DNA-integrity ca. 57 at 100 µM). Compounds 1 to 3 fulfilled some physicochemical properties to act topically on the skin.

Exploring the Influence of Spacers in EDTA-ß-Cyclodextrin Dendrimers: Physicochemical Properties and In Vitro Biological Behavior.

The synthesis of a new family of ethylenediaminetetraacetic acid (EDTA) core dimers and G0 dendrimers end-capped with two and four ß-cyclodextrin (ßCD) moieties was performed by click-chemistry conjugation, varying the spacers attached to the core. The structure analyses were achieved in DMSO-d6 and the self-inclusion process was studied in D2O by 1H-NMR spectroscopy for all platforms. It was demonstrated that the interaction with adamantane carboxylic acid (AdCOOH) results in a guest-induced shift of the self-inclusion effect, demonstrating the full host ability of the ßCD units in these new platforms without any influence of the spacer. The results of the quantitative size and water solubility measurements demonstrated the equivalence between the novel EDTA-ßCD platforms and the classical PAMAM-ßCD dendrimer. Finally, we determined the toxicity for all EDTA-ßCD platforms in four different cell lines: two human breast cancer cells (MCF-7 and MDA-MB-231), human cervical adenocarcinoma cancer cells (HeLa), and human lung adenocarcinoma cells (SK-LU-1). The new EDTA-ßCD carriers did not present any cytotoxicity in the tested cell lines, which showed that these new classes of platforms are promising candidates for drug delivery.

r/K selection of GC content in prokaryotes.

The guanine/cytosine (GC) content of prokaryotic genomes is species-specific, taking values from 16% to 77%. This diversity of selection for GC content remains contentious. We analyse the correlations between GC content and a range of phenotypic and genotypic data in thousands of prokaryotes. GC content integrates well with these traits into r/K selection theory when phenotypic plasticity is considered. High GC-content prokaryotes are r-strategists with cheaper descendants thanks to a lower average amino acid metabolic cost, colonize unstable environments thanks to flagella and a bacillus form and are generalists in terms of resource opportunism and their defence mechanisms. Low GC content prokaryotes are K-strategists specialized for stable environments that maintain homeostasis via a high-cost outer cell membrane and endospore formation as a response to nutrient deprivation, and attain a higher nutrient-to-biomass yield. The lower proteome cost of high GC content prokaryotes is driven by the association between GC-rich codons and cheaper amino acids in the genetic code, while the correlation between GC content and genome size may be partly due to functional diversity driven by r/K selection. In all, molecular diversity in the GC content of prokaryotes may be a consequence of ecological r/K selection.

Ecology theory disentangles microbial dichotomies.

Microbes are often discussed in terms of dichotomies such as copiotrophic/oligotrophic and fast/slow-growing microbes, defined using the characterisation of microbial growth in isolated cultures. The dichotomies are usually qualitative and/or study-specific, sometimes precluding clear-cut results interpretation. We can unravel microbial dichotomies as life history strategies by combining ecology theory with Monod curves, a laboratory mathematical tool of bacterial physiology that relates the specific growth rate of a microbe with the concentration of a limiting nutrient. Fitting of Monod curves provides quantities that directly correspond to key parameters in ecological theories addressing species coexistence and diversity, such as r/K selection theory, resource competition and community structure theory and the CSR triangle of life strategies. The resulting model allows us to reconcile the copiotrophic/oligotrophic and fast/slow-growing dichotomies as different subsamples of a life history strategy triangle that also includes r/K strategists. We also used the number of known carbon sources together with community structure theory to partially explain the diversity of heterotrophic microbes observed in metagenomics experiments. In sum, we propose a theoretical framework for the study of natural microbial communities that unifies several existing proposals. Its application would require the integration of metagenomics, metametabolomics, Monod curves and carbon source data.

The evolving copiotrophic/oligotrophic dichotomy: From Winogradsky to physiology and genomics.

Nearly 100 years ago, Winogradsky published a classic communication in which he described two groups of microbes, zymogenic and autochthonous. When organic matter penetrates the soil, zymogenic microbes quickly multiply and degrade it, then giving way to the slow combustion of autochthonous microbes. Although the text was originally written in French, it is often cited by English-speaking authors. We undertook a complete translation of the 1924 publication, which we provide as Supporting information. Here, we introduce the translation and describe how the zymogenic/autochthonous dichotomy shaped research questions in the study of microbial diversity and physiology. We also identify in the literature three additional and closely related dichotomies, which we propose to call exclusive copiotrophs/oligotrophs, coexisting copiotrophs/oligotrophs and fast-growing/slow-growing microbes. While Winogradsky focussed on a successional view of microbial populations over time, the current discussion is focussed on the differences in the specific growth rate of microbes as a function of the concentration of a given limiting substrate. In the future, it will be relevant to keep in mind both nutrient-focussed and time-focussed microbial dichotomies and to design experiments with both isolated laboratory cultures and multi-species communities in the spirit of Winogradsky's direct method.

Endothelial Progenitor Cells May Be Related to Major Amputation after Angioplasty in Patients with Critical Limb Ischemia.

BACKGROUND: Critical limb ischemia represents an advanced stage of peripheral arterial disease. Angioplasty improves blood flow to the limb; however, some patients progress irreversibly to lower limb amputation. Few studies have explored the predictive potential of biomarkers during postangioplasty outcomes. AIM: To evaluate the behavior of endothelial progenitor cells in patients with critical limb ischemia, in relation to their postangioplasty outcome. METHODS: Twenty patients with critical limb ischemia, candidates for angioplasty, were enrolled. Flow-mediated dilation, as well as endothelial progenitor cells (subpopulations CD45+/CD34+/CD133+/CD184+ and CD45+/CD/34+/KDR[VEGFR-2]+ estimated by flow cytometry) from blood flow close to vascular damage, were evaluated before and after angioplasty. Association with lower limb amputation during a 30-day follow-up was analyzed. RESULTS: Endothelial progenitor cells were related with flow-mediated dilation. A higher number of baseline EPCs CD45+CD34+KDR+, as well as an impaired reactivity of endothelial progenitor cells CD45+CD34+CD133+CD184+ after angioplasty, were observed in cases further undergoing major limb amputation, with a significant discrimination ability and risk (0.75, specificity 0.83 and RR 4.5 p < 0.05). CONCLUSIONS: Endothelial progenitor cells were related with endothelial dysfunction, whereas a higher baseline number of the subpopulation CD45+CD34+KDR+, as well as an impaired reactivity of subpopulation CD45+CD34+CD133+CD184+ after angioplasty, showed a predictive ability for major limb amputation in patients with critical limb ischemia.

Molecular Information Theory Meets Protein Folding.

We propose an application of molecular information theory to analyze the folding of single domain proteins. We analyze results from various areas of protein science, such as sequence-based potentials, reduced amino acid alphabets, backbone configurational entropy, secondary structure content, residue burial layers, and mutational studies of protein stability changes. We found that the average information contained in the sequences of evolved proteins is very close to the average information needed to specify a fold ∼2.2 ± 0.3 bits/(site·operation). The effective alphabet size in evolved proteins equals the effective number of conformations of a residue in the compact unfolded state at around 5. We calculated an energy-to-information conversion efficiency upon folding of around 50%, lower than the theoretical limit of 70%, but much higher than human-built macroscopic machines. We propose a simple mapping between molecular information theory and energy landscape theory and explore the connections between sequence evolution, configurational entropy, and the energetics of protein folding.

Conformational buffering underlies functional selection in intrinsically disordered protein regions.

Many disordered proteins conserve essential functions in the face of extensive sequence variation, making it challenging to identify the mechanisms responsible for functional selection. Here we identify the molecular mechanism of functional selection for the disordered adenovirus early gene 1A (E1A) protein. E1A competes with host factors to bind the retinoblastoma (Rb) protein, subverting cell cycle regulation. We show that two binding motifs tethered by a hypervariable disordered linker drive picomolar affinity Rb binding and host factor displacement. Compensatory changes in amino acid sequence composition and sequence length lead to conservation of optimal tethering across a large family of E1A linkers. We refer to this compensatory mechanism as conformational buffering. We also detect coevolution of the motifs and linker, which can preserve or eliminate the tethering mechanism. Conformational buffering and motif-linker coevolution explain robust functional encoding within hypervariable disordered linkers and could underlie functional selection of many disordered protein regions.

Transcription factor specificity limits the number of DNA-binding motifs.

We study the limits imposed by transcription factor specificity on the maximum number of binding motifs that can coexist in a gene regulatory network, using the SwissRegulon Fantom5 collection of 684 human transcription factor binding sites as a model. We describe transcription factor specificity using regular expressions and find that most human transcription factor binding site motifs are separated in sequence space by one to three motif-discriminating positions. We apply theorems based on the pigeonhole principle to calculate the maximum number of transcription factors that can coexist given this degree of specificity, which is in the order of ten thousand and would fully utilize the space of DNA subsequences. Taking into account an expanded DNA alphabet with modified bases can further raise this limit by several orders of magnitude, at a lower level of sequence space usage. Our results may guide the design of transcription factors at both the molecular and system scale.

Deamidation drives molecular aging of the SARS-CoV-2 spike protein receptor-binding motif.

The spike protein is the main protein component of the SARS-CoV-2 virion surface. The spike receptor-binding motif mediates recognition of the human angiotensin-converting enzyme 2 receptor, a critical step in infection, and is the preferential target for spike-neutralizing antibodies. Posttranslational modifications of the spike receptor-binding motif have been shown to modulate viral infectivity and host immune response, but these modifications are still being explored. Here we studied asparagine deamidation of the spike protein, a spontaneous event that leads to the appearance of aspartic and isoaspartic residues, which affect both the protein backbone and its charge. We used computational prediction and biochemical experiments to identify five deamidation hotspots in the SARS-CoV-2 spike protein. Asparagine residues 481 and 501 in the receptor-binding motif deamidate with a half-life of 16.5 and 123 days at 37 °C, respectively. Deamidation is significantly slowed at 4 °C, indicating a strong dependence of spike protein molecular aging on environmental conditions. Deamidation of the spike receptor-binding motif decreases the equilibrium constant for binding to the human angiotensin-converting enzyme 2 receptor more than 3.5-fold, yet its high conservation pattern suggests some positive effect on viral fitness. We propose a model for deamidation of the full SARS-CoV-2 virion illustrating how deamidation of the spike receptor-binding motif could lead to the accumulation on the virion surface of a nonnegligible chemically diverse spike population in a timescale of days. Our findings provide a potential mechanism for molecular aging of the spike protein with significant consequences for understanding virus infectivity and vaccine development.

Synthesis and Cytotoxic Activity of Combretastatin A-4 and 2,3-Diphenyl-2H-indazole Hybrids.

Cancer is the second leading cause of death, after cardiovascular diseases. Different strategies have been developed to treat cancer; however, chemotherapy with cytotoxic agents is still the most widely used treatment approach. Nevertheless, drug resistance to available chemotherapeutic agents is still a serious problem, and the development of new active compounds remains a constant need. Taking advantage of the molecular hybridization approach, in the present work we designed, synthesized, and tested the cytotoxic activity of two hybrid compounds and seven derivatives based on the structure of combretastatin A-4 and 2,3-diphenyl-2H-indazole. Practical modifications of reported synthetic protocols for 2-pheny-2H-indazole and 2,3-dipheny-2H-indazole derivatives under microwave irradiation were implemented. The cytotoxicity assays showed that our designed hybrid compounds possess strong activity, especially compound 5, which resulted even better than the reference drug cisplatin against HeLa and SK-LU-1 cells (IC50 of 0.16 and 6.63 µM, respectively), and it had similar potency to the reference drug imatinib against K562 cells. Additionally, in silico and in vitro studies strongly suggest tubulin as the molecular target for hybrid compound 5.

Thousands of protein linear motif classes may still be undiscovered.

Linear motifs are short protein subsequences that mediate protein interactions. Hundreds of motif classes including thousands of motif instances are known. Our theory estimates how many motif classes remain undiscovered. As commonly done, we describe motif classes as regular expressions specifying motif length and the allowed amino acids at each motif position. We measure motif specificity for a pair of motif classes by quantifying how many motif-discriminating positions prevent a protein subsequence from matching the two classes at once. We derive theorems for the maximal number of motif classes that can simultaneously maintain a certain number of motif-discriminating positions between all pairs of classes in the motif universe, for a given amino acid alphabet. We also calculate the fraction of all protein subsequences that would belong to a motif class if all potential motif classes came into existence. Naturally occurring pairs of motif classes present most often a single motif-discriminating position. This mild specificity maximizes the potential number of coexisting motif classes, the expansion of the motif universe due to amino acid modifications and the fraction of amino acid sequences that code for a motif instance. As a result, thousands of linear motif classes may remain undiscovered.

Developing synthetic biology in Argentina: the Latin American TECNOx community as an alternative way for growth of the field.

Synthetic biology emerged in the USA and Europe twenty years ago and quickly developed innovative research and technology as a result of continued funding. Synthetic biology is also growing in many developing countries of Africa, Asia and Latin America, where it could have a large economic impact by helping its use of genetic biodiversity in order to boost existing industries. Starting in 2011, Argentine synthetic biology developed along an idiosyncratic path. In 2011-2012, the main focus was not exclusively research but also on community building through teaching and participation in iGEM, following the template of the early "MIT school" of synthetic biology. In 2013-2015, activities diversified and included society-centered projects, social science studies on synthetic biology and bioart. Standard research outputs such as articles and industrial applications helped consolidate several academic working groups. Since 2016, the lack of a critical mass of researchers and a funding crisis were partially compensated by establishing links with Latin American synthetic biologists and with other socially oriented open technology collectives. The TECNOx community is a central node in this growing research and technology network. The first four annual TECNOx meetings brought together synthetic biologists with other open science and engineering platforms and explored the relationship of Latin American technologies with entrepreneurship, open hardware, ethics and human rights. In sum, the socioeconomic context encouraged Latin American synthetic biology to develop in a meandering and diversifying manner. This revealed alternative ways for growth of the field that may be relevant to other developing countries.

Efectos de un protocolo de ayuno intermitente sobre la composición corporal y perfil lipídico en estudiantes universitarios / Effects of a protocol of intermittent fasting on body composition and lipids profile in university students

El ayuno intermitente es una estrategia nutricional de creciente interés para el control del peso y mejora de la salud metabólica. El objetivo del presente estudio fue evaluar el efecto de un protocolo de ayuno intermitente sobre la composición corporal, perfil lipídico y los biomarcadores de riesgo cardiovascular en estudiantes universitarios. En este estudio experimental participaron 30 sujetos varones y fueron divididos aleatoriamente en dos grupos, 15 sujetos constituían el grupo experimental (GE) (edad: 20,83±0,98 años) y 15 el grupo control (GC) (edad: 23,71±5,55 años). El GE realizó un protocolo de ayuno 16/8, dieciséis horas de ayuno y ocho horas de ingesta calórica sin limitaciones, dos días consecutivos a la semana durante cinco semanas. Se evaluó la composición corporal, la ingesta calórica, el perfil lipídico y los biomarcadores del riesgo cardiovascular al inicio, mitad y final del protocolo. Se observaron descensos significativos en el GE en pliegues cutáneos, perímetro cintura, porcentaje de grasa, perfil lipídico y biomarcadores del riesgo cardiovascular en comparación con GC (p<0,05). Se encontraron incrementos significativos en la ingesta de colesterol y ácidos grasos poliinsaturados en el GE al final del estudio (p<0,05). Se observaron descensos en el colesterol total, triglicéridos, lipoproteínas de baja densidad y biomarcadores del riesgo cardiovascular a lo largo del protocolo en el GE (p<0,05). Un protocolo de ayuno intermitente 16/8, dos días consecutivos por semana, durante cinco semanas, parece efectivo para mejorar parámetros de composición corporal y perfil lipídico, así como para mejorar los biomarcadores relacionados con el riesgo cardiovascular(AU)

Intermittent fasting is a nutritional strategy of high interest in weight control and improvement of metabolic health. The objective of this study was to evaluate the effect of an intermittent fasting protocol on body composition, lipid profile and biomarkers of cardiovascular risk in university students. In this experimental study thirty male subjects participated and were randomly divided into two groups; fifteen subjects constituted the experimental group (GE) (age: 20.83 ± 0.98 years) and fifteen the control group (GC) (age: 23.71 ± 5.55 years). The GE performed a fasting protocol 16/8, sixteen hours of fasting and eight hours of caloric intake without limitations, two consecutive days per week for five weeks. Body composition, calorie intake, lipid profile and biomarkers of cardiovascular risk were evaluated at the beginning, middle and at the end of the protocol. Significant decreases were found in GE in skinfolds, waist perimeter, % fat, lipid profile and biomarkers of cardiovascular risk as compared to GC (p <0.05). There were significant increases in the intake of cholesterol and polyunsaturated fatty acids in the GE at the end of the study (p <0.05). There were decreases in total cholesterol, triglycerides, low-density lipoproteins, and biomarkers of cardiovascular risk throughout the study in GE (p<0.05). An intermittent fasting protocol 16/8, two consecutive days per week, for five weeks, seems effective to improve parameters of body composition and lipid profile, as well as to improving biomarkers related to cardiovascular risk(AU)

Alma Ata: experiencias que validan sus propuestas 40 años después, para proyectarlas al futuro / Alma Ata: experiences that validate your proposals 40 years later, to project them into the future

Mucho se ha discutido sobre porqué después de la Conferencia Internacional de Salud de Alma Ata de 1978, no se siguió un impulso que hiciera posible su implementación y más bien la salud discurriera por corrientes no solo distintas sino opuestas en algunos casos. Si bien es cierto que esta discusión es importante para entender mejor las lecciones aprendidas en torno a la denominada atención primaria de salud (APS), evitar los errores y profundizar sus aciertos, es más importante operativizar, en el sentido que Alma Ata propuso, modelos de salud integrales e incluyentes que reflejen la justicia, la equidad, la innovación y la audacia necesarias para construir un mundo mejor, más justo, saludable, desarrollado y feliz. En las Américas hay experiencias relativamente recientes que abogan por ello, que es importante presentar inicialmente, ya que están aún en proceso de sistematización e investigación.

Topology Dictates Evolution of Regulatory Cysteines in a Family of Viral Oncoproteins.

Redox regulation in biology is largely operated by cysteine chemistry in response to a variety of cell environmental and intracellular stimuli. The high chemical reactivity of cysteines determines their conservation in functional roles, but their presence can also result in harmful oxidation limiting their general use by proteins. Papillomaviruses constitute a unique system for studying protein sequence evolution since there are hundreds of anciently evolved stable genomes. E7, the viral transforming factor, is a dimeric, cysteine-rich oncoprotein that shows both conserved structural and variable regulatory cysteines constituting an excellent model for uncovering the mechanism that drives the acquisition of redox-sensitive groups. By analyzing over 300 E7 sequences, we found that although noncanonical cysteines show no obvious sequence conservation pattern, they are nonrandomly distributed based on topological constrains. Regulatory residues are strictly excluded from six positions stabilizing the hydrophobic core while they are enriched in key positions located at the dimerization interface or around the Zn+2 ion. Oxidation of regulatory cysteines is linked to dimer dissociation, acting as a reversible redox-sensing mechanism that triggers a conformational switch. Based on comparative sequence analysis, molecular dynamics simulations and biophysical analysis, we propose a model in which the occurrence of cysteine-rich positions is dictated by topological constrains, providing an explanation to why a degenerate pattern of cysteines can be achieved in a family of homologs. Thus, topological principles should enable the possibility to identify hidden regulatory cysteines that are not accurately detected using sequence based methodology.