The Burden Patients with Myasthenia Gravis Experience in Terms of Breathing, Fatigue, Sleep, Mental Health, Discomfort and Usual Activities in Comparison to the General Population

INTRODUCTION

Myasthenia gravis (MG) is a rare neuromuscular disorder marked by a variable combination of weakness of eye, bulbar, respiratory, axial, and limb muscles. This study compared the experience of people with MG regarding breathing, fatigue, sleep, pain/discomfort, mental health, and usual activities with the general population.

METHODS

The MyRealWorld-MG digital, multinational study enrolled patients with MG and collected demographics, PROMIS-Dyspnea, PROMIS-Sleep Disturbance, FACIT-Fatigue, EQ-5D-5L, Health Utilities Index (HUI-3), Hospital Anxiety and Depression Scale (HADS), MG-Activities of Daily Living (MG-ADL), and MG-Quality-of-Life (MG-QoL-15r). Comparisons with the general population were based on PROMIS population norms, published literature, or on data from a digital, multinational, observational study which enrolled a representative sample of the general population (POPUP).

RESULTS

In MyRealWorld-MG (N = 2074), patients experienced higher intensity, frequency, and duration of PROMIS shortness of breath than a US population (p < 0.0001). Patients with MG had higher PROMIS-Sleep Disturbance scores than POPUP (53.7 vs 50.0, p < 0.0001), and 54.9% of patients had clinically severe FACIT-Fatigue scores vs 6.8% in POPUP (p < 0.0001). Among patients with MG, 69.6% and 18.5% had moderate-to-severe HADS-Anxiety and HADS-Depression compared to 20.3% and 6.9% in POPUP (p < 0.001). Statistically significant and strong associations were found between fatigue, sleep, dyspnea, usual activities, and emotions. All outcomes worsened with more severe disease.

CONCLUSION

A considerable burden was observed in this comparison of breathing, sleep, fatigue, mental health, and usual activities between patients with MG and the general population, using data from two international studies and published population norms. Even mildly affected patients had significantly worse outcomes than the general population.

People Diagnosed with Myasthenia Gravis have Lower health-related quality of life and Need More Medical and Caregiver Help in Comparison to the General Population: Analysis of Two Observational Studies

INTRODUCTION

Myasthenia gravis (MG) is a neuromuscular disease causing extreme muscular fatigue, triggering problems with vision, swallowing, speech, mobility, dexterity, and breathing. This analysis intended to estimate the health-related quality-of-life impact, the medical burden, and the need for caregiver help of people diagnosed with MG.

METHODS

MyRealWorld-MG (MRW) is an observational study among adults diagnosed with MG in 9 countries. The General Population Norms (POPUP) observational study enrolled representative members of the general population in 8 countries. In both digital studies, respondents entered personal characteristics and provided data on medical conditions, EQ-5D-5L, HUI3, MG-Activities of Daily Living (MG-ADL), sick leave, caregiver help, and medical care utilization.

RESULTS

In MRW (n = 1859), 58.4% of respondents had moderate-to-severe MG. Average utility values were lower in MRW versus POPUP (0.739 vs. 0.843 for EQ-5D-5L; 0.493 vs. 0.746 for HUI3), and declined with more severe disease (0.872, 0.707, 0.511 EQ-5D-5L utilities and 0.695, 0.443, 0.168 HUI3 utilities for mild, moderate, and severe MG, respectively). Taking sick leave in the past month was 2.6 times more frequent among people diagnosed with MG compared to the general population (34.4% vs. 13.2%) and four times more people diagnosed with MG reported needing help from a caregiver (34.8% vs. 8.3%). Use of medical care was twice as likely in MRW in comparison with POPUP (51.9% vs. 24.6%).

CONCLUSION

This direct comparison of people diagnosed with MG and the general population using two large international studies revealed significant negative impact of MG. Results were consistent across all outcomes, in all countries.

Utilities for treatment-related adverse events in type 2 diabetes

OBJECTIVES

The impact of Type 2 diabetes mellitus (T2DM) on health-related quality-of-life (HRQoL) is complex due to the burden of disease, lifelong treatment requirements, and comorbidities. This study aimed to capture UK societal utility values for health states associated with T2DM and treatment-related adverse events (AEs) to assess the burden of the disease and common AEs.

METHODS

Nine health state descriptions were developed (from a literature review and patient and clinician qualitative input) depicting the burden associated with T2DM and treatment-related AEs. These were mild/moderate urinary tract infection (UTI); severe UTI; mycotic infection; moderate hypoglycemic events; severe hypoglycemic events; fear of hypoglycemia; gastrointestinal symptoms; and hypovolemic events. Members of the UK general public (n = 100) valued these states using the time trade-off (TTO) methodology to elicit utility values (between 0 = dead, 1 = full health). Regression analysis was conducted to understand the influence of age and gender.

RESULTS

All treatment-related AEs were found to have a significant effect on utility. From the T2DM baseline state (0.92), the experience of AEs was associated with the following disutility: T2DM with hypovolemic events (0.08); T2DM with mild/moderate UTIs (0.09); T2DM with moderate hypoglycemic events (0.11); T2DM with severe hypoglycemic events (0.15); T2DM with fear of hypoglycemia (0.15); T2DM with severe UTIs (0.19); T2DM with GI symptoms (0.24); and T2DM with mycotic infection (0.25); Males consistently scored the states with significantly lower utility values, but no significant age effects emerged.

CONCLUSIONS

Findings suggest that adverse events in T2DM can be a burden for some individuals. The study indicates the potential importance of including information regarding AEs in economic evaluations. Although some states were rated severely in terms of utility; in reality, many of these only last a few days, therefore having a minimal quality-adjusted life year (QALY) impact.

Antipsychotic prescribing to older people living in care homes and the community in England and Wales

OBJECTIVE

Excessive use of antipsychotic medication by older people is an international concern, but there is limited comparative information on their use in different residential settings. This paper describes and compares antipsychotic prescribing to older people in care homes and the community in England and Wales.

METHOD

Analysis of a primary care database (THIN) with 403 259 community and 10 387 care home residents aged 65-104 years in 2008-9.

RESULTS

3677 (0.9%) patients in the community and 2173 (20.9%) in care homes (20.5% in residential homes, 21.7% in nursing homes) received an antipsychotic medication prescription in the last 90 days. Most patients had received prescriptions for more than three months and 60% of prescriptions were for atypical antipsychotics. In patients without severe mental illness, 2367 (0.6%) patients in the community and 1765 (18.2%) in care homes received antipsychotic medication; such prescribing was common for patients with recorded dementia (30.2% in care home, 10.1% in the community). In care homes, younger age and living in the North of England predicted prescribing, but care home type did not. In the community, female gender, increasing age, living in a deprived area and the North predicted prescribing.

CONCLUSIONS

Despite safety concerns, antipsychotic prescribing is markedly higher in care homes than in the community, and strongly associated with dementia in both settings. In England and Wales, we estimate that 54 000 older care home patients and 50 000 community patients receive antipsychotic medication without a diagnosis of severe mental illness with important implications for health and social services.

Eliciting health state utilities from the general public for severe chronic pain

OBJECTIVE

There is an absence of data on public preferences for health states (HSs) associated with severe chronic pain. The aim of this study was to develop accurate HS descriptions for severe chronic pain requiring intrathecal (IT) therapy and to derive utility weights that describe the health-related quality of life (HRQL) impact of chronic pain associated with malignant (MP) and non-malignant (NMP) aetiologies.

RESEARCH DESIGN AND METHOD

Eight visual analogue scale pain index (VAS-PI) HSs were defined using ranges 0-40, 41-60, 61-80 and 81-100 applied to both MP and NMP. Additionally, eight HSs representing common adverse events associated with IT therapy were identified. The content and description of the HSs were ascertained by interviews with five United Kingdom clinical experts. In total, 16 HSs were compiled. These HS descriptions and HS questionnaires were administered to 102 members of the public, utilising a time trade off (TTO) approach to estimate utilities for the HSs.

RESULTS

Participants generally were well matched to the general public in England and Wales, with some differences in mean age, race and education. A substantial decline in utility was observed with more severe VAS-PI values. The mean TTO utility values also decreased from mild pain to severe pain. Participants were able to differentiate between the side effects.

CONCLUSION

The study shows a clear decrement in utility moving from different severity levels of severe chronic pain.

Cost-effectiveness of ziconotide in intrathecal pain management for severe chronic pain patients in the UK

OBJECTIVE

To examine the cost-effectiveness of using intrathecal ziconotide in the treatment of severe chronic pain compared to best supportive care for patients with intractable chronic pain in the United Kingdom.

METHODS

Using a simulation model, the analysis evaluated the cost and health economic consequences of using ziconotide as a treatment for severe chronic pain. The modelled population and clinical data were based on a randomised controlled trial in which the main outcome was reduction in pain as measured by the visual analogue scale of pain intensity (VASPI). Resource use data were elicited using a modified Delphi panel and costed using published sources. Utility values were derived from a separate research study. The main outcome measure was the cost per quality-adjusted life-year (QALY). Extensive scenario analysis was conducted to evaluate parameter uncertainty.

RESULTS

Overall, findings were robust to most assumptions. The cost-effectiveness of ziconotide compared to best supportive care (BSC) was pound 27,443 per QALY (95% CI pound 18,304-38,504). Scenarios were investigated in which discount rates, the time horizon, the threshold for qualifying as a responder, pump-related assumptions, utilities, ziconotide drug dose, and the patient discontinuation rate with ziconotide were varied. The most sensitive parameter was the dosage of ziconotide: using the lower and upper bounds of the average ziconotide dosage observed in the long-term open-label study changed the incremental cost-effectiveness ratio (ICER) to pound 15,500 [pound 8206-25,405] and pound 44,700 [pound 30,541-62, 670].

CONCLUSIONS

Ziconotide may offer an economically feasible alternative solution for patients for whom current treatment is inappropriate or ineffective. The main study limitation is that some model inputs, mainly related to resource use, are based on assumptions or expert interviews.

Eliciting patient preferences for hormonal therapy options in the treatment of metastatic prostate cancer

Treatment choices for metastatic prostate cancer are complex and can involve men balancing survival versus quality of life. The present study aims to elicit patient preferences with respect to the attributes of treatments for metastatic prostate cancer through a discrete choice experiment (DCE) questionnaire. Men with recently diagnosed localized prostate cancer were asked to envisage that they had metastatic disease when completing a survey. As expected, men with prostate cancer placed considerable importance on gains in survival; however, avoiding side effects of treatment was also clearly important. Survival gains should be considered alongside side effects when discussing treatment options in metastatic disease.

A combined micro-resonance Raman and absorption set-up enabling in vivo studies under varying physiological conditions: The nerve globin in the nerve cord of Aphrodite aculeata

We hereby report on the design of a set-up combining micro-resonance Raman and absorption spectroscopy with a microfluidic system. The set-up enabled us to study the nerve globin of Aphrodite aculeata in the functional isolated nerve cord under varying physiological conditions for extended periods of time. The oxygenation cycle of the organism was triggered by utilizing the microfluidic system that allowed for a fast switch between aerobic and anaerobic conditions. The nerve globin was found to very easily shift from a penta-coordinated high spin ferrous form to the oxy state upon a change from anaerobic to aerobic conditions. The observed fast reaction to varying O(2) concentrations supports an oxygen-carrying and/or -storing function of the nerve globin. In addition, by combining resonance Raman and absorption spectroscopy, the physiological response could be distinguished from light-induced effects.

Neuroglobin and cytoglobin as potential enzyme or substrate

The possible enzymatic activities of neuro- and cytoglobin as well as their potential function as substrates in enzymatic reactions were studied. Neuro- and cytoglobin are found to show no appreciable superoxide dismutase, catalase, and peroxidase activities. However, the internal disulfide bond (CD7-D5) of human neuroglobin can be reduced by thioredoxin reductase. Furthermore, our in vivo and in vitro studies show that Escherichia coli cells contain an enzymatic reducing system that keeps the heme iron atom of neuroglobin in the Fe(2+) form in the presence of dioxygen despite the high autoxidation rate of the molecule. This reducing system needs a low-molecular-weight compound as co-factor. In vitro tests show that both NADH and NADPH can play this role. Furthermore, the reducing system is not specific for neuroglobin but allows the reduction of the ferric forms of other globins such as cytoglobin and myoglobin. A similar reducing system is present in eukaryotic tissue protein extracts.

Health state utilities for metastatic breast cancer

The aim of the study was to obtain United Kingdom-based societal preferences for distinct stages of metastatic breast cancer (MBC) and six common toxicities. Health states were developed based on literature review, iterative cycles of interviews and a focus group with clinical experts. They described the burden of progressive, responding and stable disease on treatment; and also febrile neutropenia, stomatitis; diarrhoea/vomiting; fatigue; hand-foot syndrome (grade 3/4 toxicities) and hair loss. One hundred members of the general public rated them using standard gamble to determine health state utility. Data were analysed with a mixed model analysis. The study sample was a good match to the general public of England and Wales by demographics and current quality of life. Stable disease on treatment had a utility value of 0.72, with a corresponding gain of +0.07 following a treatment response and a decline by 0.27 for disease progression. Toxicities lead to declines in utility between 0.10 (diarrhoea/vomiting) and 0.15 (febrile neutropenia). This study underlines the value that society place on the avoidance of disease progression and severe side effects in MBC. This may be the largest preference study in breast cancer designed to survey a representative general public sample.

The economic value of anti-IgE in severe persistent, IgE-mediated (allergic) asthma patients: adaptation of INNOVATE to Sweden

BACKGROUND

Severe allergic asthma patients may not be controlled even with guideline recommended care, including inhaled corticosteroids, long-acting beta-2 agonists, theophylline, oral steroids and anti-leukotrienes. They experience exacerbations requiring intensive healthcare use and which may be fatal. Omalizumab, a new monoclonal antibody for use in IgE-mediated allergic diseases, reduces exacerbations and daily symptoms in this patient population. The aim of this study is to estimate the cost effectiveness of adding omalizumab to optimized standard therapy (ST) in patients with severe persistent IgE-mediated (allergic) asthma.

METHODS

A Markov model comparing lifelong ST with a treatment period of omalizumab add-on therapy followed by ST, was developed based on efficacy data from the INNOVATE trial (28 weeks, N = 419) and Swedish life table and cost data. This model assumes that patients are at risk of having an exacerbation every 2 weeks and are at risk of dying from a clinically significant severe asthma exacerbation. Patients in a steady-state of having no exacerbations are defined to be in an 'optimized asthma control' state. Resource use data and utilities were obtained from INNOVATE and from a UK observational study. Costs from a societal perspective include estimates for drugs, routine care, exacerbations and costs in added years of life; benefits are expressed in QALYs. The response to omalizumab was evaluated after 16 weeks of trial, and non-responders stopped taking omalizumab for the remaining time.

RESULTS

Total lifetime discounted costs and QALYs on ST were 52,702 euros and 11.60. Omalizumab add-on therapy cost an additional 42,754 euros for 0.76 additional QALYs, resulting in an incremental cost-effectiveness ratio of 56,091 euros. A probabilistic sensitivity analysis indicates that the 95% CI around the ICER is [31,328 euros; 120,552 euros]. One-way analyses indicate that the results are sensitive to the exacerbation-related mortality rate, the time horizon and the discount rates.

CONCLUSIONS

Based on the model and the assumptions used, our results suggest that omalizumab provides cost offsets, improves quality of life and may have an attractive ICER in treating the severe allergic asthma population.

Analyzing heme proteins using EPR techniques: the heme-pocket structure of ferric mouse neuroglobin

In this work, an electron paramagnetic resonance (EPR) strategy to study the heme-pocket structure of low-spin ferric heme proteins is optimized. Frozen solutions of ferric mouse neuroglobin (mNgb) are analyzed by means of electron spin echo envelope modulation and pulsed electron-nuclear double resonance techniques. The hyperfine and nuclear quadrupole couplings of the directly coordinating heme and histidine nitrogens are derived and are discussed in comparison with known data of other ferric porphyrin compounds. In combination with the hyperfine matrices of the imidazole protons, the 14N EPR parameters reveal structural information on the heme pocket of mNgb that is in agreement with previous X-ray diffraction data on neuroglobins.

Effects of short-term hypoxia on neuroglobin levels and localization in mouse brain tissues

Nerve cells are highly susceptible to ischemic and hypoxic injuries. The neuroglobin (Ngb), found in vertebrate nerve cells, has been suggested to protect nerve cells from ischemic episodes by a yet unknown mechanism. However, contradicting reports exist regarding localization and up-regulation of Ngb in response to hypoxia. The aim of the present study was to probe the distribution of Ngb proteins in mouse brain and retina by immunohistochemistry, and to quantify the levels of Ngb mRNA by reverse-transcription-polymerase chain reaction (RT-PCR) after short-term (2 h) exposure to 7.6% oxygen. We found Ngb to be present throughout the neocortex, most abundantly in the perirhinal, entorhinal and temporal cortical areas, the thalamus and hypothalamus, the choroid plexus, the olfactory bulb and the cranial nerve nuclei in the brainstem. Intense staining was observed in the mesencephalic central grey area and the Purkinje cells. Two-hour hypoxic exposure caused no detectable changes in staining intensity or spatial distribution of Ngb neither in the Purkinje cells nor in any other brain areas observed. The RT-PCR data supported the lack of differences in brain Ngb levels between normal and oxygen-deprived animals. In the retina, Ngb localization by immunohistochemistry was confined to the inner segments of the photoreceptors, the plexiform layers and the ganglion cells. Short-termed hypoxia did not change retinal Ngb levels as assessed by both techniques. The lack of Ngb up-regulation in the brain is consistent with results from previous long-term hypoxic experiments, suggesting that Ngb is not regulated by pure hypoxia in vivo.

Nerve globins in invertebrates

The expression of nerve hemoglobins in invertebrates is a well-established fact, but this occurrence is uncommon. In the species where nerve globins occur, they probably function as an oxygen store for sustaining activity of the nerves during anoxic conditions. Although invertebrate nerve globins are functionally similar with respect to O2 affinity, they are by no means uniform in structure and can differ in size, cellular localization and heme-coordination. The best-studied nerve globin is the mini-globin of Cerebratulus lacteus, which belongs to a class of globins containing the polar TyrB10/GlnE7 pair in the distal pocket. The amide and phenol side chains normally cause low rates of O2 dissociation and ultra-high O2 affinity by forming strong hydrogen bonds with bound ligands. Cerebratulus hemoglobin, however, has a moderate O2 affinity, due to the presence of a third polar amino-acid in its active site, ThrE11, which inhibits hydrogen bonding to bound oxygen by the B10 tyrosine side chain.

Hypoxia/ischemia and the regulation of neuroglobin and cytoglobin expression

In analogy to hemoglobin (Hb) and myoglobin (Mb), neuroglobin (Ngb) and cytoglobin (Cygb) are supposed to be involved in oxygen (O2) storage and delivery. The Cygb gene harbours both conserved HREs and mRNA stabilization sites, strongly suggestive of an oxygen-dependent regulation. We examined the relative transcriptional changes of Ngb and Cygb in a situation of chronic hypoxia using real-time quantitative PCR. We could conclude that Cygb is a hypoxia-induced gene, which is transcriptionally upregulated during chronic hypoxia in a hippocampal neuronal cell line and in multiple murine metabolically active tissues. The mechanism of induction of Cygb is HIF-1alpha dependent. HIF-1 is unique among mammalian transcription factors with respect to the specificity and sensitivity of its induction by hypoxia. Ngb expression seems to be regulated using other response elements and is less influenced by hypoxia.

Tracing the structure-function relationship of neuroglobin and cytoglobin using resonance Raman and electron paramagnetic resonance spectroscopy

The physiological role of neuroglobin and cytoglobin, two vertebrate globins discovered in the last 5 years, is not yet clearly understood. In this work, we review the structural information on these globins and its implication on the possible protein function, obtained by electron paramagnetic resonance and resonance Raman spectroscopy. All studies reveal a high flexibility in the heme-pocket region of neuroglobin. Together with the observation that the distal ligand of the heme iron is the endogenous E7-histidine in both the ferric and ferrous form of neuroglobin and cytoglobin, the flexibility of the heme environment in neuroglobin will play a crucial role in the globins' ability to bind and stabilize exogenous ligands.

Cytoglobin expression is upregulated in all tissues upon hypoxia: an in vitro and in vivo study by quantitative real-time PCR

The vertebrate globin family has been extended with two members: neuroglobin and cytoglobin. We here investigate the changes of expression levels upon hypoxia of cytoglobin in parallel with neuroglobin, in vivo and in vitro, by using real-time quantitative PCR. Our data prove that cytoglobin is upregulated upon hypoxia in all tissues. The mechanism of induction of cytoglobin is regulated by the hypoxia-inducible factor 1, a posttranscriptionally regulated transcription factor controlling several hypoxia-inducible genes. The latter is argumented by: (1) cytoglobin is significantly upregulated upon hypoxia and this is dependent on the tissue and severity of hypoxia; (2) the regulation of cytoglobin expression in HIF-1 (+/-) knockout mice is affected; (3) the variations of the expression regulation are in the same manner as seen in the expression of our control gene VEGF, that is proven to be regulated by the HIF-1-pathway; and (4) cytoglobin promoter region contains HRE sites.

Crystallization and preliminary X-ray analysis of neural haemoglobin from the nemertean worm Cerebratulus lacteus

The nemertean worm Cerebratulus lacteus neural tissue haemoglobin (109 amino acids, the shortest known haemoglobin) has been overexpressed in Escherichia coli, purified and crystallized. A highly redundant native data set has been collected at the Cu K(alpha) wavelength to 2.05 A resolution. The crystals belong to the orthorhombic P2(1)2(1)2(1) space group, with unit-cell parameters a = 42.5, b = 43.1, c = 60.2 A and one molecule per asymmetric unit. The anomalous difference Patterson map clearly reveals the position of the haem Fe atom, thus paving the way for MAD/SAD structure determination.

Biochemical characterization and ligand binding properties of neuroglobin, a novel member of the globin family

Neuroglobin is a recently discovered member of the globin superfamily that is suggested to enhance the O(2) supply of the vertebrate brain. Spectral measurements with human and mouse recombinant neuroglobin provide evidence for a hexacoordinated deoxy ferrous (Fe(2+)) form, indicating a His-Fe(2+)-His binding scheme. O(2) or CO can displace the endogenous protein ligand, which is identified as the distal histidine by mutagenesis. The ferric (Fe(3+)) form of neuroglobin is also hexacoordinated with the protein ligand E7-His and does not exhibit pH dependence. Flash photolysis studies show a high recombination rate (k(on)) and a slow dissociation rate (k(off)) for both O(2) and CO, indicating a high intrinsic affinity for these ligands. However, because the rate-limiting step in ligand combination with the deoxy hexacoordinated form involves the dissociation of the protein ligand, O(2) and CO binding is suggested to be slow in vivo. Because of this competition, the observed O(2) affinity of recombinant human neuroglobin is average (1 torr at 37 degrees C). Neuroglobin has a high autoxidation rate, resulting in an oxidation at 37 degrees C by air within a few minutes. The oxidation/reduction potential of mouse neuroglobin (E'(o) = -129 mV) lies within the physiological range. Under natural conditions, recombinant mouse neuroglobin occurs as a monomer with disulfide-dependent formation of dimers. The biochemical and kinetic characteristics are discussed in view of the possible functions of neuroglobin in the vertebrate brain.

The primary structure of globin and linker chains from the chlorocruorin of the polychaete Sabella spallanzanii

Annelid hemoglobins are organized in a very complex supramolecular network of interacting polypeptides, the structure of which is still not wholly resolved. We have separated by two-dimensional electrophoresis the 4-MDa chlorocruorin of Sabella spallanzanii and identified its components by amino-terminal sequencing. This work reveals a high rate of heterogeneity of constituent chains in a single animal as well as in the Sabella population. Using a cDNA library prepared from the hematopoietic tissue of this worm, we have isolated and fully sequenced most globin and linker cDNAs. The primary structure features of these polypeptides have been characterized by comparison with model globin and linker sequences.

The evolution of extracellular hemoglobins of annelids, vestimentiferans, and pogonophorans

The evolution of extracellular hemoglobins of annelids, vestimentiferans, and pogonophorans was investigated by applying cladistic and distance-based approaches to reconstruct the phylogenetic relationships of this group of respiratory pigments. We performed this study using the aligned sequences of globin and linker chains that are the constituents of these complex molecules. Three novel globin and two novel linker chains of Sabella spallanzanii described in an accompanying paper (Pallavicini, A., Negrisolo, E., Barbato, R., Dewilde, S., Ghiretti-Magaldi, A., Moens, L., and Lanfranchi, G. (2001) J. Biol. Chem. 276, 26384--26390) were also included. Our results allowed us to test previous hypotheses on the evolutionary pathways of these proteins and to formulate a new most parsimonious model of molecular evolution. According to this novel model, the genes coding for the polypeptides forming these composite molecules were already present in the common ancestor of annelids, vestimentiferans, and pogonophorans.

Very high resolution structure of a trematode hemoglobin displaying a TyrB10-TyrE7 heme distal residue pair and high oxygen affinity

Monomeric hemoglobin from the trematode Paramphistomum epiclitum displays very high oxygen affinity (P(50)<0.001 mm Hg) and an unusual heme distal site containing tyrosyl residues at the B10 and E7 positions. The crystal structure of aquo-met P. epiclitum hemoglobin, solved at 1.17 A resolution via multiwavelength anomalous dispersion techniques (R-factor=0.121), shows that the heme distal site pocket residue TyrB10 is engaged in hydrogen bonding to the iron-bound ligand. By contrast, residue TyrE7 is unexpectedly locked next to the CD globin region, in a conformation unsuitable for heme-bound ligand stabilisation. Such structural organization of the E7 distal residue differs strikingly from that observed in the nematode Ascaris suum hemoglobin (bearing TyrB10 and GlnE7 residues), which also displays very high oxygen affinity. The oxygenation and carbonylation parameters of wild-type P. epiclitum Hb as well as of single- and double-site mutants, with residue substitutions at positions B10, E7 and E11, have been determined and are discussed here in the light of the protein atomic resolution crystal structure.

Protein and gene structure of a chlorocruorin chain of Eudistylia vancouverii

The polychaete annelid, Eudistylia vancouverii, contains as oxygen carrier a hexagonal bilayer (HBL) chlorocruorin. One of the globin chains, chain a1, has 142 amino acids (Mr 16,054.99) and its sequence deviates strongly from other nonvertebrate globin sequences. Unprecedented, it displays a Phe at the distal position E7 as well as at position B10, creating a very hydrophobic heme pocket probably responsible for the low oxygen affinity of the native molecule. Phylogenetic analysis of annelid globin chains clearly proves that globin chain a1 belongs to type I of globin chains having a pattern of 3 cysteine residues essential for the aggregation into a HBL structure. The gene coding for globin chain a1 is interrupted by 2 introns at the conserved positions B12.2 and G7.0. Based on protein and gene structure it can therefore be concluded that the globin chains of chlorocruorins are not fundamentally different from other annelid globin chains.

Ligand binding in the ferric and ferrous states of Paramecium hemoglobin

The unicellular protozoan Paramecium caudatum contains a monomeric hemoglobin (Hb) that has only 116 amino acid residues. This Hb shares the simultaneous presence of a distal E7 glutamine and a B10 tyrosine with several invertebrate Hbs. In the study presented here, we have used ligand binding kinetics and resonance Raman spectroscopy to characterize the effect of the distal pocket residues of Paramecium Hb in stabilizing the heme-bound ligands. In the ferric state, the high-spin to low-spin (aquo-hydroxy) transition takes place with a pK(a) of approximately 9.0. The oxygen affinity (P(50) = 0.45 Torr) is similar to that of myoglobin. The oxygen on- and off-rates are also similar to those of sperm whale myoglobin. Resonance Raman data suggest hydrogen bonding stabilization of bound oxygen, evidenced by a relatively low frequency of Fe-OO stretching (563 cm(-1)). We propose that the oxy complex is an equilibrium mixture of a hydrogen-bonded closed structure and an open structure. Oxygen will dissociate preferentially from the open structure, and therefore, the fraction of open structure population controls the rate of oxygen dissociation. In the CO complex, the Fe-CO stretching frequency at 493 cm(-1) suggests an open heme pocket, which is consistent with the higher on- and off-rates for CO relative to those in myoglobin. A high rate of ligand binding is also consistent with the observation of an Fe-histidine stretching frequency at 220 cm(-1), indicating the absence of significant proximal strain. We postulate that the function of Paramecium Hb is to supply oxygen for cellular oxidative processes.

Isohemoglobin differentiation in the bimodal-breathing amazon catfish Hoplosternum littorale

The bimodal gill(water)/gut(air)-breathing Amazonian catfish Hoplosternum littorale that frequents hypoxic habitats uses "mammalian" 2,3-diphosphoglycerate (DPG) in addition to "piscine" ATP and GTP as erythrocytic O(2) affinity modulators. Its electrophoretically distinct anodic and cathodic hemoglobins (Hb(An) and Hb(Ca)) were isolated for functional and molecular characterization. In contrast to Hb(An), phosphate-free Hb(Ca) exhibits a pronounced reverse Bohr effect (increased O(2) affinity with decreasing pH) that is obliterated by ATP, and opposite pH dependences of K(T) (O(2) association constant of low affinity, tense state) and the overall heat of oxygenation. Dose-response curves indicate small chloride effects and pronounced and differentiated phosphate effects, DPG < ATP < GTP < IHP. Hb(Ca)-O(2) equilibria analyzed in terms of the Monod-Wyman-Changeux model show that small T state bond energy differences underlie the differentiated phosphate effects. Synthetic peptides, corresponding to N-terminal fragment of the cytoplasmic domain of trout band 3 protein, undergo oxygenation-linked binding to Hb(Ca), suggesting a metabolic regulatory role for this hemoglobin. The amino acid sequences for the alpha and beta chains of Hb(Ca) obtained by Edman degradation and cDNA sequencing show unusual substitutions at the phosphate-binding site that are discussed in terms of its reverse Bohr effect and anion sensitivities.

A novel two-over-two alpha-helical sandwich fold is characteristic of the truncated hemoglobin family

Small hemoproteins displaying amino acid sequences 20-40 residues shorter than (non-)vertebrate hemoglobins (Hbs) have recently been identified in several pathogenic and non-pathogenic unicellular organisms, and named 'truncated hemoglobins' (trHbs). They have been proposed to be involved not only in oxygen transport but also in other biological functions, such as protection against reactive nitrogen species, photosynthesis or to act as terminal oxidases. Crystal structures of trHbs from the ciliated protozoan Paramecium caudatum and the green unicellular alga Chlamydomonas eugametos show that the tertiary structure of both proteins is based on a 'two-over-two' alpha-helical sandwich, reflecting an unprecedented editing of the classical 'three-over-three' alpha-helical globin fold. Based on specific Gly-Gly motifs the tertiary structure accommodates the deletion of the N-terminal A-helix and replacement of the crucial heme-binding F-helix with an extended polypeptide loop. Additionally, concerted structural modifications allow burying of the heme group and define the distal site, which hosts a TyrB10, GlnE7 residue pair. A set of structural and amino acid sequence consensus rules for stabilizing the fold and the bound heme in the trHbs homology subfamily is deduced.

A hemoglobin with an optical function

Hemoglobins are best known as oxygen transport proteins. Here we describe a hemoglobin from the parasitic nematode Mermis nigrescens (Mn-GLB-E) that has an optical, light shadowing function. The protein accumulates to high concentration as intracellular crystals in the ocellus of mature phototactic adult females while also being expressed at low concentration in other tissues. It differs in sequence and expression pattern from Mn-GLB-B, a second Mermis globin. It retains the structure and oxygen-binding and light-absorbing properties typical of nematode hemoglobins. As such, recruitment to a shadowing role in the eye appears to have occurred by changes in expression without modification of biochemistry. Both globins are coded by genes interrupted by two introns at the conserved positions B12.2 and G7.0, which is in agreement with the 3exon/2intron pattern model of globin gene evolution.

Daphnia pulex didomain hemoglobin: structure and evolution of polymeric hemoglobins and their coding genes

The high-molecular-weight extracellular hemoglobin of Daphnia pulex is composed of at least three different didomain globin chains. The primary structure of one of these chains was determined at the protein and cDNA levels. Each globin domain of the polypeptide chain displays the standard structural characteristics. The first domain is preceded by a 30-residue extension containing an 18-residue unprecedented threonine-rich segment and a 12-residue preA segment which is homologous to the preA segments of other nonvertebrate globin chains. Both domains are linked together by a preA' segment, which is homologous to other preA segments and lacks the threonine-rich segment. Dimerization of the globin chains by the formation of a disulphide bridge linking the unique cysteines near the amino-termini results in a covalent, vertebrate-like tetradomain structure. The flexible amino-terminal extension most likely facilitates dimerization. The gene coding for this globin chain is interrupted by six small introns. Each domain displays two intradomain introns at the conserved positions B12.2 and G7.0. A precoding intron occurs at position preA(-27.0) and a bridge intron at occurs preA'(-13.2). We propose a crossover event as the most likely mechanism for duplication. Arthropod globin trees reflect the added effects of gene diversification, gene duplication, and species evolution. The position of monodomain intracellular globins in the tree suggests that they resemble the ancestral globin more than the derived didomain extracellular globins do.

Structural, functional, and genetic characterization of Gastrophilus hemoglobin

Hemoglobin of Gastrophilus intestinalis (Insecta, Diptera), was purified and characterized. At least two isoforms have been identified by isoelectrofocusing, mass spectrometry, and genomic Southern blotting. Functional studies show a high oxygen affinity due to a low ligand dissociation rate (koff = 2.4 s-1) and a relatively high autoxidation rate (t1/2 = 1.6/h). The globins were separated under denaturing conditions, and the sequence of Hb1 (Mr = 17,965 +/- 2) was determined at the protein and DNA level. The open reading frame codes for a polypeptide of 150 amino acids. Although the globin is distantly related to globins from other species, it has a low penalty score against globin templates. Freshly isolated hemoglobin was crystallized from polyethylene glycol. Crystals contain two hemoglobin molecules per asymmetric unit. Solution of the three-dimensional structure by molecular replacement could not be achieved, possibly due to the presence of three protein isoforms in the crystals. In order to determine its three-dimensional structure, G. intestinalis Hb1 was overexpressed in Escherichia coli, resulting in a fully functional molecule as confirmed by ligand binding affinity. The globin gene contains two introns at positions D7.0 and G7.0. The D7.0 intron is unprecedented, suggesting that globin gene evolution is much more complex than originally thought.

Characterization of the myoglobin and its coding gene of the mollusc Biomphalaria glabrata

A cDNA clone isolated from a Biomphalaria glabrata (Mollusca, Gastropoda) neural cDNA library was identified as encoding a myoglobin-like protein of 148 amino acids with a single domain and a calculated mass of 16,049.29. Alignment with globin sequences with known tertiary structure confirms its overall globin nature. The expressed myoglobin was identified in the radular muscle and isolated. Oxygen equilibrium measurements on the protein reveal a high oxygen affinity. Val-B10 and Gln-E7, important residues for the determination of the oxygen affinity, are strikingly different from the standard molluscan pattern (Conti, E., Moser, C., Rizzi, M., Mattevi, A., Lionetti, C., Coda, A., Ascenzi, P., Brunori, M., Bolognesi, M. (1993) J. Mol. Biol. 233, 498-508). The single gene encoding the globin chain is interrupted by three introns at positions A3.2, B12.2, and G7.0. Comparison with other nonvertebrate globin genes reveals on the one hand conservation (B12.2 and G7.0) and on the other hand variability of the insertion positions (A3.2). The Biomphalaria myoglobin sequence was used together with all other molluscan globin sequences available to assess the origin and phylogeny of the phylum. Our results confirm the doubts raised about monophyletic origin of the Mollusca, which was first observed using SSU rRNA as a molecular marker.

Trematode myoglobins, functional molecules with a distal tyrosine

The myoglobins of two trematodes, Paramphistomum epiclitum and Isoparorchis hypselobagri, were isolated to homogeneity. The native molecules are monomeric with Mr 16,000-17,000 and pI 6.5-7.5. In each species, at least four different globin isoforms occur. Primary structure was determined at the protein level. The globin chains contain 147 amino acid residues. Although major determinants of the globin fold are conserved, characteristic substitutions are present. A Tyr residue occurs at the helical positions B10 and E7 (distal position). This is confirmed by NMR measurements (Zhang, W., Rashid, K. A., Haque, M., Siddiqi, A. H., Vinogradov, S. N., Moens, L. & La Mar, G. N. (1997) J. Biol. Chem. 272, 3000-3006). A distal Tyr normally provokes oxidation of the iron atom and the inability to bind oxygen, whereas a Tyr-B10 is indicative for a high oxygen affinity. In contrast, trematode myoglobins are functional molecules with a high oxygen affinity. Molecular modeling predicts two possible positions for the aromatic ring of Tyr-E7: one being outside the heme pocket making it freely accessible to the ligand and one within the heme pocket potentially able to form a second hydrogen bond with the iron-bound oxygen. A hydrogen bond between Tyr-B10 and the bound oxygen as in the Ascaris hemoglobin is predicted as well. The predicted structure may explain the high oxygen affinity of the trematode myoglobins.

Globin and globin gene structure of the nerve myoglobin of Aphrodite aculeata

The globin of the nerve cord of the polychaete annelid Aphrodite aculeata was isolated and purified to homogeneity. The native molecule has a pI of 6.3 and acts as a dimer of two identical Mr 15, 644.5 polypeptide chains as determined by electrospray mass spectrometry. It has an average affinity for oxygen (P50 = 1.24 torr) resulting from fast association (kon = 170 X 10(6) M-1 . s-1) and dissociation rates (koff = 360 s-1). The partial primary structure of this nerve globin was determined at the protein level and completed and confirmed by translation of the cDNA sequence. The globin chain has 150 amino acid residues and a calculated Mr of 15, 602.69 strongly suggesting that the amino terminus is acetylated. The absence of a leader sequence and the lack of Cys at the positions NA2 and H9 needed for the formation of the high Mr complexes found in extracellular annelid globins classify the Aphrodite globin with the cellular globin species. The Aphrodite nerve globin is unlikely to represent a separate globin family, as cDNA derived primers detect globin messenger RNA in muscle, gut, and pharynx tissue as well. The gene encoding this globin species is interrupted by a single intron, inserted at position G7.0. Comparison to other globin gene structures strongly suggest that introns can be lost independently, rather than simultaneously as a result of a single conversion event as suggested previously (Lewin, R. (1984) Science 226, 328).

A fairly conserved epitope on the hemagglutinin of influenza A (H3N2) virus with variable accessibility to neutralizing antibody

A monoclonal antibody LMBH5 was derived from mice which had been immunized with A/Victoria/3/75 (H3N2)-type recombinant, secreted hemagglutinin (HA), and were subsequently challenged with a potentially lethal dose of X31 [A/Aichi/2/68 (H3N2) x A/PR/8/34 (H1N1)] virus. LMBH5 reacted strongly with the native and low-pH-induced conformations of the HA of A/Aichi (X31 strain) and A/Victoria (X47 strain), but very weakly with the native structure of the HA of A/Philippines/2/82 (X79 strain) and not at all with the HA of A/Guizhou/54/89 H3 (NIB25 strain). However, the acid-induced conformations of the latter two viruses were recognized by LMBH5. The antibody prevented infection of MDCK cells with X31 and X47, whereas X79 virus was partially neutralized by LMBH5. X31 monoclonal escape variants had single amino acid substitutions (Ser 227-->Pro) near the interface. The data obtained suggest that the neutralizing LMBH5 reacts with a fairly conserved epitope of influenza A (H3N2) virus, which as a result of antigenic drift becomes inaccessible in the native state of the HA.