Flavodoxins: sequence, folding, binding, function and beyond

Flavodoxins are electron-transfer proteins involved in a variety of photosynthetic and non-photosynthetic reactions in bacteria, whereas, in eukaryotes, a descendant of the flavodoxin gene helps build multidomain proteins. The redox activity of flavodoxin derives from its bound flavin mononucleotide cofactor (FMN), whose intrinsic properties are profoundly modified by the host apoprotein. This review covers the very exciting last decade of flavodoxin research, in which the folding pathway, the structure and stability of the apoprotein, the mechanism of FMN recognition, the interactions that stabilize the functional complex and tailor the redox potentials, and many details of the binding and electron transfer to partner proteins have been revealed. The next decade should witness an even deeper understanding of the flavodoxin molecule and a greater comprehension of its many physiological roles. The fact that flavodoxin is essential for the survival of some human pathogens could make it a drug target on its own.

Equilibrium Φ-Analysis of a Molten Globule: The 1-149 Apoflavodoxin Fragment

The apoflavodoxin fragment comprising residues 1-149 that can be obtained by chemical cleavage of the C-terminal alpha-helix of the full-length protein is known to populate a molten globule conformation that displays a cooperative behaviour and experiences two-state urea and thermal denaturation. Here, we have used a recombinant form of this fragment to investigate molten globule energetics and to derive structural information by equilibrium Phi-analysis. We have characterized 15 mutant fragments designed to probe the persistence of native interactions in the molten globule and compared their conformational stability to that of the equivalent full-length apoflavodoxin mutants. According to our data, most of the mutations analysed modify the stability of the molten globule fragment following the trend observed when the same mutations are implemented in the full-length protein. However, the changes in stability observed in the molten globule are much smaller and the Phi-values calculated are (with a single exception) below 0.4. This is consistent with an overall and significant debilitation of the native structure. Nevertheless, the fact that the molten globule fragment can be stabilised using as a guide the native structure of the full-length protein (by increasing helix propensity, optimising charge interactions and filling small cavities) suggests that the overall structure of the molten globule is still quite close to native, in spite of the lowered stability observed.

[Respiratory muscle aids during an episode of aspiration in a patient with Duchenne muscular dystrophy]

We report the case of a Duchenne muscular dystrophy patient with good bulbar function but severely decreased forced vital capacity (9%) and spontaneous peak cough flow (PCF) (2.35 L/s). The patient needed continuous noninvasive ventilation (NIV) consisting of a volumetric ventilator with a nighttime nasal mask and a daytime mouthpiece. He also required application of manually assisted coughing techniques by insufflation with a resuscitation bag and chest thrust (manually assisted PCF after maximum insufflation capacity of 4.33 L/s). An episode of serious food aspiration was resolved by his main caregiver through NIV and manually assisted coughing. Bronchoscopy under sedation using NIV with a lip seal connection to his volumetric ventilator later revealed that no material remained. This case exemplifies the potential role of skilled respiratory management in some neuromuscular diseases.

[Quality of the health care to the epileptic patients in Spain]

INTRODUCTION

The objective of the study was to evaluate the quality of the health care to the epileptic patient in Spain including recently diagnosed patients, controlled patients and medically refractory patients.

METHODS

Throughout years 2001-2002 a questionnaire of consensus was agreed by neurologists from surgical epilepsy units, epilepsy units, community hospitals and outpatient clinics.

RESULTS

A total of 139 questionnaires were analysed. Only one third of the hospitals had a specialized epilepsy clinic. The longest waiting lists for diagnostic procedures were video EEG and Holter EEG, with 175 and 97.6 days, respectively. Clear differences between autonomous communities as far as availability of neurologists on duty, availability of diagnostic tests and number of epilepsy units are stated, existing, in general, more resources in the autonomous communities with health transferred before 2002 and Madrid.

CONCLUSIONS

As much the lack of resources as the inequalities indicate that we are still far from the quality standards recommended by the International League Against Epilepsy (ILAE), lacking a suitable lanning that eliminates the inequalities and it so approaches us a system of assistance integrated in different levels as it is set out by the international scientific community.

[Neonatal screening of glucose-6-phosphate dehydrogenase deficiency in umbilical cord blood]

Glucose-6-phosphate dehydrogenase (G6PD) deficiency is the most frequent enzyme deficiency. It is a sex-linked genetic disease concerning mostly african, mediterranean and far-eastern populations. The main clinical expression is a hemolytic anemia which can be acute or chronic. During the neonatal period the disease may manifest as neonatal jaundice. We have been asked by the neonate department to set up a blood screening test for this deficiency. We have therefore developed a test using umbilical cord blood. The assay of G6PD has been automatised and red blood cell aspartate-amino-transferase (ASAT) chosen as a reference enzyme to evaluate the age of red blood cells. Normal values of G6PD, ASAT and G6PD/ASAT ratio have been calculated from 235 cord samples. Genetic frequency of this deficiency in 2002 was 6% in male and 1% in female newborns.

Quality of life and psychometric functionality in patients with differentiated thyroid carcinoma

We studied the psychological performance and the quality of life in patients with differentiated thyroid carcinoma, either during treatment with chronic suppressive doses of levothyroxine, or during the withdrawal of levothyroxine needed to perform whole-body scanning with radioactive iodine, with those of appropriate healthy controls. Eighteen women with differentiated thyroid carcinoma and 18 euthyroid age-matched healthy women were recruited. Patients were studied the day before levothyroxine withdrawal (when in chronic mild or subclinical hyperthyroidism), 4-7 days later (when most patients had normal serum free thyroxine and free triiodothyronine levels), and the day before scanning (when in profound hypothyroidism). Controls were studied at one time point. When compared with controls, patients presented with impairment of several indexes during chronic suppressive levothyroxine therapy (total score, emotional, sleep, energy and social of the Nottingham Health Profile; mental health, general health and social function of the SF-36, and total score on Wais Digit Span; P<0.05 for all comparisons). Also, quality of life indexes (19 of 21 scores), cognitive tests (6 of 12 scores), and affective and physical symptoms visual mental scales (18 of 19) worsened during profound hypothyroidism (P<0.05 for all comparisons). Quality of life and cognitive performance were almost comparable with those of euthyroid controls when most patients had normal free thyroxine and triiodothyronine levels. In conclusion, quality of life and psychometric functionality in patients with differentiated thyroid carcinoma is not only affected by withdrawal of levothyroxine but also by long-term treatment with supraphysiological doses of levothyroxine.

Non-invasive management of an acute chest infection for a patient with ALS

We describe a man diagnosed with non-bulbar amyotrophic lateral sclerosis (ALS) who uses 24-h non-invasive ventilator at home, and assisted cough through the use of the mechanical insufflation-exsufflation (MAC) device (CoughAssist, J.H. Emerson). This was essential for the removal of bronchial secretions in order to provide successful non-invasive management (and indeed less suffering for the patient) during an acute respiratory tract infection with hypoxemia and failure of manually assisted cough.

Obesity, and not insulin resistance, is the major determinant of serum inflammatory cardiovascular risk markers in pre-menopausal women

AIMS/HYPOTHESIS

Increased serum inflammatory markers have been found in obesity and insulin-resistant states, and could play a causative role in insulin resistance, atherosclerosis and cardiovascular disease. The polycystic ovary syndrome represents a human model of insulin resistance because both lean and obese polycystic ovary syndrome patients are insulin-resistant compared with non-hyperandrogenic women. We evaluated whether obesity, insulin resistance, or both, are related to the increased concentrations of inflammatory markers in pre-menopausal women.

METHODS

We compared 35 patients with polycystic ovary syndrome and 28 healthy women, paired for BMI, prevalence of obesity and smoking. Measurements included serum inflammatory markers, BMI, waist-to-hip ratio, blood pressure, serum glucose, insulin, lipid and hormone concentrations, and insulin sensitivity index.

RESULTS

The insulin sensitivity index was reduced in polycystic ovary syndrome patients compared with controls. However, no differences were observed between both groups in C-reactive protein, interleukin 6, tumour necrosis factor-alpha, soluble type 2 tumour necrosis factor receptor, and soluble intercellular cell adhesion molecule-1. When considering patients and controls as a whole, C-reactive protein and interleukin 6, were increased in obese subjects compared with lean women. Inverse correlations existed between insulin sensitivity index and C-reactive protein, interleukin 6, tumour necrosis factor-alpha, soluble type 2 tumour necrosis factor receptor, and soluble intercellular cell adhesion molecule-1. Only the weak correlation with C-reactive protein persisted after controlling for BMI.

CONCLUSION/INTERPRETATION

Obesity, and not insulin resistance, is the major determinant of serum inflammatory cardiovascular risk markers in pre-menopausal women.

Apoflavodoxin folding mechanism: an alpha/beta protein with an essentially off-pathway intermediate

The folding reaction of Anabaena apoflavodoxin has been studied by stopped-flow kinetics and site-directed mutagenesis. Although the urea unfolding equilibrium is two-state, a transient intermediate accumulates during the folding reaction. The intermediate is monomeric, and it is not related to proline isomerization. Unlike many cases where the presence of an intermediate has been detected either by a burst phase or by the curvature, at low urea concentration, of the otherwise only observable kinetic phase, two kinetic phases are observed in apoflavodoxin folding whose total amplitude equals the amplitude of unfolding. To determine the role of the intermediate in the folding reaction, the apoflavodoxin kinetic data have been fitted to all conceivable three-species kinetic models (either linear or triangular). Using a stepwise fitting procedure, we find that the off-pathway mechanism explains most of the kinetic data (not a slow unfolding phase), the on-pathway mechanism being rejected. By using global analysis, good overall agreement between data and fit is found when a triangular mechanism is considered. The fitted values of the microscopic constants indicate that most of the unfolded molecules refold from the denatured state. Apoflavodoxin thus folds via a triangular, but essentially off-pathway, mechanism. We calculate that the retardation of the folding caused by the off-pathway intermediate is not large. Some unusual properties of the intermediate are discussed.

Receiver operating characteristic analysis of the performance of basal serum hormone profiles for the diagnosis of polycystic ovary syndrome in epidemiological studies

OBJECTIVE

We have used receiver operating characteristic (ROC) analysis to determine the diagnostic performance of several serum parameters, in order to evaluate their potential usefulness in establishing the diagnosis of polycystic ovary syndrome (PCOS) in epidemiological studies.

DESIGN

Prospective study.

METHODS

One hundred and fourteen women reporting spontaneously for blood donation were included in the study. Menopausal and oral contraceptive-treated women were excluded. Serum samples were obtained at the moment of donation, independently of fasting, time of day or day of menstrual cycle. Measurements included total testosterone, sex hormone-binding globulin (SHBG), dehydroepiandrosterone sulfate (DHEAS), LH, FSH and estradiol. The free testosterone (FT) concentration and the free androgen index (FAI) were calculated from testosterone and SHBG levels. ROC curves were calculated for all these serum determinations.

RESULTS

Eight patients were diagnosed with PCOS, according to the presence of oligomenorrhea, hirsutism, acne and/or hyperandrogenemia, and exclusion of non-classic congenital adrenal hyperplasia, hypothyroidism and hyperprolactinemia. Of the parameters studied SHBG, FAI, FT and DHEAS were considered adequate measures for the diagnosis of PCOS. For example, serum SHBG levels showed an area under the ROC curve of 0.875+/-(S.E.(w))0.045 (95% confidence interval 0.800-0.929). A SHBG decision threshold <37 nmol/l had a sensitivity of 87.5%, a specificity of 86.8%, a positive likelihood ratio of 6.63, and a negative likelihood ratio of 0.14, for the diagnosis of PCOS.

CONCLUSIONS

Our present results strongly suggest that decreased SHBG levels, and increased FAI, free testosterone concentration and DHEAS concentrations, are highly effective as single analytical procedures in epidemiological studies for the detection of PCOS in women of reproductive age.

TNF-alpha and hyperandrogenism: a clinical, biochemical, and molecular genetic study

To evaluate the role of TNF-alpha in the pathogenesis of hyperandrogenism, we have evaluated the serum TNF-alpha levels, as well as several polymorphisms in the promoter region of the TNF-alpha gene, in a group of 60 hyperandrogenic patients and 27 healthy controls matched for body mass index. Hyperandrogenic patients presented with mildly increased serum TNF-alpha levels as compared with controls (mean[median] +/- SD: 7.2[7.0] +/- 3.3 pg/ml vs. 5.6[4.4] +/- 4.0 pg/ml, P < 0.02). Although no differences in body mass index and insulin resistance indexes were observed between patients and controls, when subjects were classified by body weight, serum TNF-alpha was increased only in lean patients as compared with lean controls, but this difference was not statistically significant when comparing obese patients with obese controls. The TNF-alpha gene polymorphisms studied here (-1196C/T, -1125G/C, -1031T/C, -863C/A, -857C/T, -316G/A, -308G/A, -238G/A, and -163G/A) were equally distributed in hyperandrogenic patients and controls. However, carriers of the -308A variant presented with increased basal and leuprolide-stimulated serum androgens and 17-hydroxyprogesterone levels when considering patients and controls as a group. No differences were observed in serum TNF-alpha levels, body mass index, and insulin resistance indexes, depending on the presence or absence of these variants. In conclusion, our present results suggest that the TNF-alpha system might contribute to the pathogenesis of hyperandrogenism, independent of obesity and insulin resistance. However, elucidation of the precise mechanisms underlying the relationship between the TNF-alpha system and androgen excess is needed before considering TNF-alpha as a significant contributing factor to the development of hyperandrogenism.

Anabaena apoflavodoxin hydrogen exchange: on the stable exchange core of the alpha/beta(21345) flavodoxin-like family

An important issue in modern protein biophysics is whether structurally homologous proteins share common stability and/or folding features. Flavodoxin is an archetypal alpha/beta protein organized in three layers: a central beta-sheet (strand order 21345) flanked by helices 1 and 5 on one side and helices 2, 3, and 4 on the opposite side. The backbone internal dynamics of the apoflavodoxin from Anabaena is analyzed here by the hydrogen exchange method. The hydrogen exchange rates indicate that 46 amide protons, distributed throughout the structure of apoflavodoxin, exchange relatively slowly at pH 7.0 (k(ex) < 10(-1) min(-1)). According to their distribution in the structure, protein stability is highest on the beta-sheet, helix 4, and on the layer formed by helices 1 and 5. The exchange kinetics of Anabaena apoflavodoxin was compared with those of the apoflavodoxin from Azotobacter, with which it shares a 48% sequence identity, and with Che Y and cutinase, two other alpha/beta (21345) proteins with no significant sequence homology with flavodoxins. Both similarities and differences are observed in the cores of these proteins. It is of interest that a cluster of a few structurally equivalent residues in the central beta-strands and in helix 5 is common to the cores.