Obesidad: ¿un riesgo para la enfermedad de alzheimer? II. Conectando terapias / Obesity: a risk for Alzheimer's disease? II. Connecting therapies

Cada vez son más los estudios que sugieren que la obesidad y la Enfermedad de Alzheimer (EA) son trastornos crónicos conectados mediante mecanismos patogénicos comunes, siendo la resistencia a la acción de la insulina (RAI) una pieza clave, generalmente inducida por procesos pro-inflamatorios. La obesidad se puede considerar un desencadenante de la EA (ver la primera parte de la monografía) (1). Teniendo en cuenta que la EA es un proceso patológico que actualmente no tiene un eficaz tratamiento preventivo o curativo, es de especial importancia prevenir y combatir todos los factores de riesgo de EA. Siendo un factor muy importante la obesidad y sus consecuencias patológicas (muchas de ellas concomitantes con la EA, como la diabetes tipo II - DT2). La obesidad está aumentando en todo el mundo y ya es un grave problema sanitario en muchos países. Tanto como medida de salud general de la población, como cuando se dan los primeros síntomas en un individuo en concreto (a cualquier edad, desde la juventud a la senectud), se debe implantar un régimen de vida adecuado (estilo de vida saludable, ejercicio, ausencia de estrés, dieta adecuada) para prevenir la obesidad. En algunos casos leves, pueden emplearse ciertos medicamentos, pero estos están especialmente indicados en casos crónicos refractarios a tratamientos no farmacológicos. Muchos de estos medicamentos tienen efectos también sobre la diabetes tipo 2 así como sobre la neurodegeneración que conduce a la EA en las fases más iniciales del proceso. En esta parte de la monografía se revisan especialmente los tratamientos farmacológicos, reseñando las substancias que se emplean en la actualidad, y los efectos de la alimentación en el proceso patológico común

At present, more and more studies suggest that obesity and Alzheimer's Disease (AD) are chronic disorders connected by common pathogenic mechanisms, being the resistance to the action of insulin (RAI) a key element, generally induced by proinflammatory processes. Obesity can be considered a trigger for AD (see the first part of this monograph) (1). Taking into account that AD is a pathological process that does not currently have an effective preventive or curative treatment, it is especially important to prevent and combat all risk factors for AD. Being a very important of these factors obesity and its pathological consequences (many of them concomitant with AD, such as type 2 diabetes), the study of the pharmacological and non-pharmacological treatments of these pathological situations are of prime importance. Obesity is increasing worldwide and is already a serious health problem in many countries. Both as a measure of general health of the population, and when the first symptoms occur in a particular individual (at any age, from youth to old age), an appropriate life regime must be implemented (healthy lifestyle, exercise, absence of stress, adequate diet) to prevent obesity. In some mild cases, certain medications may be used, but these are especially indicated in chronic cases refractory to nonpharmacological treatments. Many of these drugs also have effects on type 2 diabetes as well as neurodegeneration that lead to AD in the early stages of the process. In this part of the monograph, pharmacological treatments, indicating the substances that are currently used, and the effects of feeding on the common pathological process, are reviewed

Defective Insulin Signalling, Mediated by Inflammation, Connects Obesity to Alzheimer Disease; Relevant Pharmacological Therapies and Preventive Dietary Interventions.

BACKGROUND: Recent evidence suggests that obesity, besides being a risk factor for cardiovascular events, also increases the risk of Alzheimer's disease. Insulin resistance is common in all cases of obesity and appears to be the linkage between both diseases. Obesity, often associated with excessive fat and sugar intake, represents a preclinical stage toward insulin resistance during which nutrition intervention is likely to have maximum effect. OBJECTIVE: In this way, healthy lifestyles lifetime to prevent obesity-related modifiable risk factors such as inflammation, oxidative stress and metabolic disorders could be simultaneously beneficial for preserving cognition and controlling the Alzheimer's disease. METHOD: This review relates extensive research literature on facts linking nutrients and dietary patterns to obesity and Alzheimer's disease. In addition briefly presents molecular mechanisms involved in obesity- induced insulin resistance and the contribution of peripheral inflammatory and defective insulin signalling pathways, as well as ectopic lipids accumulation to Alzheimer's development through brain inflammation, neuronal insulin resistance, and cognitive dysfunction seen in Alzheimer's disease. RESULTS: The work relates current and emerging pharmacological and non-pharmacological therapies for the management of obesity, insulin resistance and Alzheimer's considering them as disorders with common molecular features. CONCLUSION: The findings of this review validate the importance of some nutritional interventions as possible approach to prevent or delay simultaneously progression of Alzheimer's disease and obesity.

Obesidad: ¿un riesgo para la enfermedad de Alzheimer? I. Mecanismos moleculares comunes / Obesity: a risk for Alzheimer's disease? I. Common molecular mechanisms

La obesidad es un factor de riesgo reconocido para las enfermedades cardiovasculares y el principal responsable de la resistencia a la acción de la insulina, estado que precede al desarrollo de diabetes de tipo 2. En los últimos años, las investigaciones han demostrado que existen además mecanismos moleculares comunes entre la obesidad y la enfermedad de Alzheimer, siendo el vínculo patológico más probable un estado de resistencia a la insulina que es mediado por inflamación. Si la disfunción cerebral en el Alzheimer efectivamente comparte mecanismos subyacentes con la obesidad, ciertas moléculas de señalización intracelular podrían estar involucradas en ambas enfermedades. La identificación de estas moléculas y su consideración como dianas terapéuticas supondrían un gran avance en el conocimiento de los mecanismos de estas enfermedades, y una buena estrategia en el desarrollo de nuevas terapias para ambos trastornos. En este trabajo se revisan las últimas hipótesis que vinculan la obesidad con Alzheimer. Se describe la disfunción del tejido adiposo y su consecuente acumulación de grasa ectópica como origen de estados sistémicos de inflamación y de resistencia a la insulina, característicos de la obesidad. Asimismo, se destacan estos estados sistémicos patológicos periféricos como principales responsables de estados de neuroinflamación y de resistencia a la insulina en el cerebro que conllevarían al deterioro cognitivo y disfunción neuronal encontrados en la enfermedad de Alzheimer

Obesity is a recognized risk factor for cardiovascular diseases and the main responsible for the resistance to the action of insulin, a state that precedes the development of diabetes type 2. In the last years, researches have demonstrated that there are also common molecular mechanisms between obesity and Alzheimer's disease, to be the more likely pathological link a state of insulin resistance, which is mediated by inflammation. If the brain dysfunction in Alzheimer's effectively shares underlying mechanisms with obesity, certain intracellular signaling molecules might be involved in both diseases. Identification of these molecules and their consideration as therapeutic targets would represent a breakthrough in the understanding of the mechanisms of these diseases, and an excellent strategy in the development of new therapies for both pathologic conditions. In this work the last hypothesis linking obesity with Alzheimer's disease are reviewed. Adipose tissue dysfunction and consequent accumulation of ectopic fat as a cause of inflammation and insulin resistance systemic conditions obesity characteristics are described. It also highlights these peripheral systemic pathological states as primarily responsible for neuroinflammation and insulin resistance in the brain that would lead to the neuronal dysfunction and cognitive impairment found in Alzheimer's disease

The Health Potential of Fruits and Vegetables Phytochemicals: Notable Examples.

Fruit and vegetables are essential components of a healthy diet. The World Health Organization (WHO) recommends an intake of five to eight portions (400-600 g) daily of fruits and vegetables to reduce risk of cardiovascular disease, cancer, poor cognitive performance, and other diet-related diseases, as well as for the prevention of micronutrient deficiencies. Much of their potential for disease prevention is thought to be provided by phytochemicals, among which the preventive activity of antioxidants is most well documented. Since numerous meta-studies published indicate variable and often contradictory results about the impact of isolated phytochemicals on health, their consumption as supplements must be carried out with care, because doses may exceed the recommended nutritional intake. Nonetheless, there is a general consensus that whole fruit and vegetable intake is more important in providing health benefits than that of only one of their constituent, because of additive and synergistic effects. This review describes the most recent literature regarding the health benefits of some selected fruits and vegetables. Importantly, since some phytochemicals regulate the same genes and pathways targeted by drugs, diets rich in fruits and vegetables in combination with medical therapies are being considered as novel approaches to treatment. Therefore, phytochemicals in fruits and vegetable might be a promising tool for the prevention and/or amelioration of a wide range of diseases.

Modulation of cholesterol-related gene expression by ergosterol and ergosterol-enriched extracts obtained from Agaricus bisporus.

PURPOSE: To investigate the effect of two extracts obtained from Agaricus bisporus on the mRNA expression of cholesterol-related genes. One of the extracts contained ergosterol and other fungal sterols (SFE) and the other contained ß-glucans and fungal sterols (EßG). METHODS: Firstly, the dietary mixed micelles (DMMs) generated after in vitro digestion of standards and SFE were applied to Caco2 cells. Then, the lower compartment after a Caco2-transport experiment was applied to HepG2 cells. The mRNA expression was assessed in both cell lines by low-density arrays (LDA). Mice received the extracts, ergosterol or control drugs after 4 weeks of a high-cholesterol diet. The lipid profile of plasma, liver and feces was determined. LDA assays were performed in liver and intestines. RESULTS: The DMM fraction of SFE up-regulated the LDLR mRNA expression in Caco2 cells. The lower compartment after Caco2-transport experiments up-regulated LDLR and modulated several other lipid-related genes in HepG2 cells. In mice, SFE decreased TC/HDL ratio and reduced hepatic triglycerides paralleled with down-regulation of Dgat1 expression, while EßG did it without transcriptional changes. Addition of SFE or ergosterol induced in jejunum a similar transcriptional response to simvastatin and ezetimibe; they all down-regulated Srebf2 and Nr1h4 (FXR) genes. CONCLUSION: Ergosterol-containing extracts from A. bisporus lowered hepatic triglyceride and modify the mRNA expression of cholesterol-related genes although the transcriptional regulation was unrelated to changes in plasma lipid profile. These extracts may be useful limiting hepatic steatosis and as bioactive ingredients to design novel functional foods preventing lifestyle-related diseases such as non-alcoholic fatty liver disease.

Effect of Selenium-Enriched Agaricus bisporus (Higher Basidiomycetes) Extracts, Obtained by Pressurized Water Extraction, on the Expression of Cholesterol Homeostasis Related Genes by Low-Density Array.

Culinary-medicinal mushrooms are able to lower blood cholesterol levels in animal models by different mechanisms. They might impair the endogenous cholesterol synthesis and exogenous cholesterol absorption during digestion. Mushroom extracts, obtained using pressurized water extractions (PWE) from Agaricus bisporus basidiomes, supplemented or not supplemented with selenium, were applied to HepG2 cell cultures to study the expression of 19 genes related to cholesterol homeostasis by low-density arrays (LDA). Only the PWE fractions obtained at 25°C showed 3-hydroxy-3-methylglutaryl-CoA reductase (HMGCR) inhibitory activity. Besides the enzymatic inhibition, PWE extracts may downregulate some of the key genes involved in the cholesterol homeostasis, such as the squalene synthase gene (FDFT1), since its mRNA expression falls by one third of its initial value. In summary, A. bisporus extracts may also modulate biological cholesterol levels by molecular mechanisms further than the enzymatic way previously reported.

In vitro Hypolipidemic and Antioxidant Effects of Leaf and Root Extracts of Taraxacum Officinale.

Adipose tissue dysfunction constitutes a primary defect in obesity and might link this disease to severe chronic health problems. We aimed to evaluate the antioxidant activity of three extracts from Taraxacum officinale (dandelion) as well as their effects on mature 3T3-L1 adipocytes concerning intracellular lipid accumulation and cytotoxicity, this would give indications regarding therapeutic interest of dandelion as potential anti-obesity candidate. Antioxidant activities of extracts from dandelion roots and leaves were evaluated in vitro using 1,1-diphenyl-2-picrylhyorazyl (DPPH) and Ferric Reducing Antioxidant Power (FRAP) methods at the concentration range used in cellular assays (300-600 µg/mL). The influence of the extracts on mature 3T3-L1 adipocyte viability was determined by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. Lipid content was determined by Oil-red-O staining. The extracts showed effective antioxidant activity correlating with total flavonoid and polyphenol contents. However, the functionality level was weakly associated with the antioxidant activity. Further, our data demonstrated that mature 3T3-L1 adipocytes reduced in size and number when incubated with the extracts, which suggests a significant increase in lipolysis activity. Particularly, leaf extract and crude powdered root of dandelion reduced triglyceride accumulation in mature 3T3-L1 adipocytes to a greater extent that the extract from the root. Our study shows anti-lipogenic effects of dandelion extracts on adipocytes as well as radical scavenging and reducing activity. Importantly, along with previous results indicating that cell populations cultivated in the presence of the dandelion extracts decrease in 3T3-L1 adipogenesis capacity, these results suggests that these extracts might represent a treatment option for obesity-related diseases by affecting different processes during the adipocyte life cycle.

A Comprehensive In Silico Analysis of the Functional and Structural Impact of Nonsynonymous SNPs in the ABCA1 Transporter Gene.

Disease phenotypes and defects in function can be traced to nonsynonymous single nucleotide polymorphisms (nsSNPs), which are important indicators of action sites and effective potential therapeutic approaches. Identification of deleterious nsSNPs is crucial to characterize the genetic basis of diseases, assess individual susceptibility to disease, determinate molecular and therapeutic targets, and predict clinical phenotypes. In this study using PolyPhen2 and MutPred in silico algorithms, we analyzed the genetic variations that can alter the expression and function of the ABCA1 gene that causes the allelic disorders familial hypoalphalipoproteinemia and Tangier disease. Predictions were validated with published results from in vitro, in vivo, and human studies. Out of a total of 233 nsSNPs, 80 (34.33%) were found deleterious by both methods. Among these 80 deleterious nsSNPs found, 29 (12.44%) rare variants resulted highly deleterious with a probability >0.8. We have observed that mostly variants with verified functional effect in experimental studies are correctly predicted as damage variants by MutPred and PolyPhen2 tools. Still, the controversial results of experimental approaches correspond to nsSNPs predicted as neutral by both methods, or contradictory predictions are obtained for them. A total of seventeen nsSNPs were predicted as deleterious by PolyPhen2, which resulted neutral by MutPred. Otherwise, forty two nsSNPs were predicted as deleterious by MutPred, which resulted neutral by PolyPhen2.

Reduction of adipogenesis and lipid accumulation by Taraxacum officinale (Dandelion) extracts in 3T3L1 adipocytes: an in vitro study.

In this in vitro study, we have investigated the ability of Taraxacum officinale (dandelion) to inhibit adipocyte differentiation and lipogenesis in 3T3-L1 preadipocytes. HPLC analysis of the three plant extracts used in this study-leaf and root extracts and a commercial root powder-identified caffeic and chlorogenic acids as the main phenolic constituents. Oil Red O staining and triglyceride levels analysis showed decreased lipid and triglyceride accumulation, respectively. Cytotoxicity was assessed with the MTT assay showing non-toxic effect among the concentrations tested. DNA microarray analysis showed that the extracts regulated the expression of a number of genes and long non-coding RNAs that play a major role in the control of adipogenesis. Taken together, our results indicate that the dandelion extracts used in this study may play a significant role during adipogenesis and lipid metabolism, and thus, supporting their therapeutic interest as potential candidates for the treatment of obesity.

Dietary phytochemicals in cancer prevention and therapy: a complementary approach with promising perspectives.

The population is aging. Over the coming years, the incidence of age-related chronic diseases such as cancer is expected to continue to increase. Phytochemicals, which are non-nutritive chemicals found in plants and food, have emerged as modulators of key cellular signaling pathways exerting proven anticancer effects. The challenge now is to develop personalized supplements comprised of specific phytochemicals for each clinical situation. This will be possible once a better understanding is gained of the molecular basis explaining the impact of phytochemicals on human health. The aim of the present literature review is to summarize current knowledge of the dietary phytochemicals with proven antitumor activity, with a special emphasis placed on their molecular targets. Also discussed are the limits of existing research strategies and the future directions of this field.

Diverse biological activities of dandelion.

Dandelion (Taraxacum officinale Weber) is a member of the Asteraceae (Compositae) family, native to Europe but widely distributed in the warmer temperate zones of the Northern Hemisphere. Dandelion and its parts are habitually consumed as plant foods in several areas of the world, where they are also employed in phytotherapy. Indeed, dandelion contains a wide array of phytochemicals whose biological activities are actively being explored in various areas of human health. In particular, emerging evidence suggests that dandelion and its constituents have antioxidant and anti-inflammatory activities that result in diverse biological effects. The present review provides a comprehensive analysis of the constituents of dandelion, an assessment of the pharmacological properties of dandelion, and a description of relevant studies that support the use of dandelion as a medicinal plant.

Dietary phytochemicals and their potential effects on obesity: a review.

The incidence of obesity is rising at an alarming rate and is becoming a major public health concern with incalculable social costs. Indeed, obesity facilitates the development of metabolic disorders such as diabetes, hypertension, and cardiovascular diseases in addition to chronic diseases such as stroke, osteoarthritis, sleep apnea, some cancers, and inflammation-bases pathologies. In this review we summarize the progresses made in our understanding of obesity, including the role of inflammation process, the recently understood endocrine function of adipose tissue, as well as passive roles of processes of energy storage and adipogenesis related to fat cell lifecycle: differentiation, maturation, and apoptosis. In addition, the article discusses the anti-obesity potential of dietary phytochemicals and analyzes their mechanisms of action, e.g. induction of apoptosis and lipolysis and inhibition of inflammation.

Improving real-time measurement of H/D exchange using a FTIR biospectroscopic probe.

We describe the improvement of a novel approach to investigating hydrogen/deuterium (H/D) exchange kinetics in biomolecules using transmission infrared spectroscopy. The method makes use of a Fourier transform infrared spectrometer coupled with a microdialysis flow cell to determine exchange rates of labile hydrogens. With this cell system, the monitoring of exchange reactions has been studied here as a function of some cell characteristics such as: (a) dialysis membrane surface contacting both the H(2)O and D(2)O compartments; (b) molecular cutoff of dialysis membrane; and (c) distance between the cell-filling holes. The best improvement has been obtained by increasing the dialysis membrane surface followed by increase of molecular cutoff. However, not significant differences were found using various distances between filling holes. The fastest exchange rate which can be measured with the cell system used here is found to be k = 0.41 +/- 0.02 min(-1), that is, about threefold greater than the one got in a previous work. This microdialysis flow cell has been used here for the study of H/D exchange in nucleic acids with subsequent structural analysis by 2D correlation spectroscopy.

Core protein-nucleic acid interactions in hepatitis C virus as revealed by Raman and circular dichroism spectroscopy.

Molecular interactions required for hepatitis C virus (HCV) assembly are not well known and are poorly understood. The 5' untranslated region (5'UTR) of the RNA genome is highly conserved and has extensive secondary structure, and the highly basic core protein is rich in arginine residues. Using Raman and circular dichroism (CD) spectroscopies, specific interactions have been demonstrated here between the 5'UTR sequence and the core protein that may be important for the specific encapsidation of the viral genome during HCV replication. These interactions can be described as follows: (1) hydrogen bonding of arginine with unpaired guanine and/or with wobble GU base pairs, and arginine-phosphate electrostatic contacts; (2) although the percentage of base pairs in the A-form is maintained in 5'UTR, the HCVc-120 protein is beta-sheet and beta-helix enriched upon formation of protein-5'UTR macromolecular assemblies; (3) protein-5'UTR interactions resulting in protein alpha-helix formation involve guanine bases in duplex segments. The mentioned interactions may represent novel targets for antiviral strategies against this important virus.

Spectroscopic study of conformational changes accompanying self-assembly of HCV core protein.

Electron microscopy and infrared and Raman spectroscopy have been used here to study the morphology, size distribution, secondary and tertiary structures of protein particles assembled from a truncated hepatitis C virus (HCV) core protein covering the first 120 aa. Particles of pure protein, having similar morphology and size distribution of those of nucleocapsids found in sera from HCV-infected patients, have been visualized for the first time. The secondary structure of these protein particles involve beta-sheet enrichment in relation to its protein monomer. Tertiary/quaternary structure has also been studied using the dynamics of H/D exchange. With this aim infrared spectra were measured as a function of H/D exchange time and subsequently analyzed by principal component analysis and two-dimensional correlation spectroscopy. Temporal dynamics of exchange for these protein particles were as follows: arginine residues exchanged first, followed by turn and unordered structures, followed by beta-sheets which may act as linkers of protein monomers.

Structural characterization of the 5' untranslated RNA of hepatitis C virus by vibrational spectroscopy.

Raman and FTIR spectroscopy have been used to characterize the structure of 5'untranslated region (5'UTR, 342-mer RNA) of the HCV genome. The study of the 750-850 cm(-1) Raman spectral domain of the ribose-phosphate backbone reveals that the percentage of nucleobases involved in double helix-loop junctions is 19+/-1%, which is very close to that of a theoretical secondary structure model (18.7%) proposed on the basis of comparative sequence analysis and thermodynamic modelling. In addition, about 68+/-2% of the bases are helically ordered having C(3')-endo ribofuranose pucker. FTIR-monitored H/D exchange provides the following results: (a) base-paired guanine and cytosine nucleobases show the lowest rate of isotopic exchange, and some synchronous intensity changes of marker bands of A.U pair and single stranded adenine are consistent with the presence of A(*)A.U triplets; (b) the vibrational coupling between the ribose ether C-O stretching and 2'OH bending motions reveals that helical regions of 5'UTR RNA are characterized by hydrogen bonding between the 2'OH ribose groups and the ether oxygen atoms of neighbouring ribose residues.

New accessory for studies of isotopic 1H/2H exchange and biomolecular interactions using transmission infrared spectroscopy.

We present here a new accessory for IR transmission measurements of 1H/2H exchange, as an ancillary tool for monitoring structural features of biomolecules in aqueous solution. This new accessory results from the combination of two dialysis membranes and a conventional liquid cell having two cylinders containing 2H2O buffer. When compared with conventional transmission measurements, carried out either after dissolving lyophilized biomolecules in 2H2O or after dialyzing the aqueous solution considered against 2H2O buffer, this accessory shows the following advantages: (1) controlled measurements over the initial steps of this isotopic exchange and absence of molecular aggregation, and (2) smaller sample amounts. This new Fourier transform IR cell can also be used to analyze ligand-biomolecule and drug-cell interactions.

On the role of arginine-glutamic acid ion pair in the ATP hydrolysis.

The complex between adenosine triphosphate (ATP) and 4-guanidinobutyric acid (GBA) has been studied by infrared spectroscopy dry and hydrated (60% relative humidity). Partial nonenzymic hydrolysis has been detected, as deduced from characteristic bands of adenosine diphosphate (ADP) and inorganic orthophosphate formation. An infrared continuum, which increases upon hydration, demonstrates that the hydrogen bonded system in this complex has a large proton polarizability due to collective proton fluctuation. On this basis, a mechanism for splitting of lytic water molecules is also discussed.

Raman study of the thermal behaviour and conformational stability of basic pancreatic trypsin inhibitor.

We have studied the thermal denaturation of native basic pancreatic trypsin inhibitor (BPTI) by monitoring the Raman bands in the 4000-400 cm(-1) range. In agreement with results obtained by calorimetry, a cooperative melting transition is observed starting at 75 degrees C. This transition is found to involve predominantly the unfolding of helical structures accompanied by beta-aggregation, loss of hydrophobic interactions between side chains and changes in CSSC dihedral angles. However, salt bridge breaking starts near 40 degrees C, as deduced from the nu(s)(COO(-)) band and from the bands close to 1320 and 1345 cm(-1) which for the first time have been shown to be due largely to vibrations of the arginine guanidyl group in BPTI. The thermal stability is, hence, attributable to cooperative contributions from hydrophobic and backbone hydrogen bond interactions as well as from disulfide bonds.

Structural roles of subunit cysteines in the folding and assembly of the DNA packaging machine (portal) of bacteriophage P22.

The DNA packaging machine (portal assembly) of bacteriophage P22 is constructed from 12 copies of a multidomain 725-residue subunit comprising a complex alpha/beta fold. The portal subunit contains four cysteines (Cys 153, Cys 173, Cys 283, and Cys 516), which produce distinctive Raman markers in the spectral interval 2500-2600 cm(-1) originating from S-H bond-stretching vibrations diagnostic of S-H...X hydrogen-bonding interactions. The Raman spectrum is unique in the capability to characterize cysteine sulfhydryl interactions in proteins and shows that portal cysteine environments are significantly altered by assembly (Rodriguez-Casado et al. (2001) Biochemistry 40, 13583-13591). We have employed site-directed mutagenesis, size-exclusion chromatography, and Raman difference spectroscopy to characterize the roles of portal cysteines in subunit folding and dodecamer assembly. The stability of the portal monomer is severely reduced by a Cys --> Ser point mutation introduced at either residue 173 or 516. In the case of C516S, the destabilized monomer still forms portal rings, as visualized by negative-stain electron microscopy, whereas portal ring formation cannot be detected for C173S, which forms aberrant aggregates. The C283S mutant is a hyperstable monomer that is defective in portal ring formation. Interestingly, Cys 283 is suggested by secondary structure homology with the phi29 portal to be within a domain involved in DNA translocation. Conversely, the phenotype of the C153S mutant is close to that of the wild-type protein, implying that the sulfhydryl moiety of Cys 153 is not essential to formation of the native subunit fold and productive assembly dynamics. The present results demonstrate that cysteines of the P22 portal protein span a wide range of sulfhydryl hydrogen-bonding strengths in the wild-type assembly, that three of the four sulfhydryls play key roles in portal protein stability and assembly kinetics, and that substitution of a mutant seryl interaction (O-H...X) for a wild-type cysteinyl interaction (S-H...X) can either stabilize or destabilize the native fold depending upon sequence context.