Identifying On-Surface Site-Selective Chemical Conversions by Theory-Aided NEXAFS Spectroscopy: The Case of Free-Base Corroles on Ag(111).

We demonstrate here that theory-assisted near-edge X-ray absorption fine-structure (NEXAFS) spectroscopy enables the site-sensitive monitoring of on-surface chemical reactions, thus, providing information not accessible by other techniques. As a prototype example, we have used free-base 5,10,15-tris(pentafluorophenyl)corroles (3H-TpFPC) adsorbed on Ag(111) and present a detailed investigation of the angle-dependent NEXAFS of this molecular species as well as of their thermally induced derivatives. For this, we have recorded experimental C and N K-edge NEXAFS spectra and interpret them based on XAS cross-section calculations by using a continuous fraction approach and core-hole including multiprojector PAW pseudopotentials within DFT. We have characterized the as-deposited low temperature (200 K) phase and unraveled the subsequent changes induced by dehydrogenation (at 330 K) and ring-closure reactions (at 430 K). By exemplarily obtaining profound insight into the on-surface chemistry of free-base corrolic species adsorbed on a noble metal this work highlights how angle-dependent XAS combined with accurate theoretical modeling can serve for the investigation of on-surface reactions, whereby even highly similar molecular structures, such as tautomers and isomers, can be distinguished.

Investigating the molecule-substrate interaction of prototypic tetrapyrrole compounds: adsorption and self-metalation of porphine on Cu(111).

We report on the adsorption and self-metalation of a prototypic tetrapyrrole compound, the free-base porphine (2H-P), on the Cu(111) surface. Our multitechnique study combines scanning tunneling microscopy (STM) results with near-edge X-ray absorption fine-structure (NEXAFS) and X-ray photoelectron spectroscopy (XPS) data whose interpretation is supported by density functional theory calculations. In the first layer in contact with the copper substrate the molecules adsorb coplanar with the surface as shown by angle-resolved NEXAFS measurements. The quenching of the first resonance in the magic angle spectra of both carbon and nitrogen regions indicates a substantial electron transfer from the substrate to the LUMO of the molecule. The stepwise annealing of a bilayer of 2H-P molecules sequentially transforms the XP and NEXAFS signatures of the nitrogen regions into those indicative of the coordinated nitrogen species of the metalated copper porphine (Cu-P), i.e., we observe a temperature-induced self-metalation of the system. Pre- and post-metalation species are clearly discriminable by STM, corroborating the spectroscopic results. Similar to the free-base porphine, the Cu-P adsorbs flat in the first layer without distortion of the macrocycle. Additionally, the electron transfer from the copper surface to the molecule is preserved upon metalation. This behavior contrasts the self-metalation of tetraphenylporphyrin (2H-TPP) on Cu(111), where both the molecular conformation and the interaction with the substrate are strongly affected by the metalation process.

Structure-function relationships and clinical applications of L-asparaginases.

L-asparaginase (L-ASNase, EC 3.5.1.1) catalyzes the hydrolysis of the non-essential amino acid L-Asn to LAsp and ammonia and is widely used for the treatment of haematopoetic diseases such as acute lymphoblastic leukaemia (ALL) and lymphomas. Therapeutic forms of L-ASNase come from different biological sources (primarily E. coli and Erwinia chrysanthemi). It is well established that the various preparations have different biochemical pharmacology properties, and different tendency to induce side-effects. This is due to different structural, physicochemical and kinetic properties of L-ASNases from the various biological sources. Understanding these properties of various L-ASNases would allow a better decipherment of their catalytic and therapeutic features, thus enabling more accurate predictions of the behaviour of these enzymes under a variety of therapeutic conditions. In addition, detailed understanding of the catalytic mechanism of L-ASNases might permit the design of new forms of L-ASNases with optimal biochemical properties for clinical applications. In this paper we review the available biochemical and pharmacokinetic information of the therapeutic forms of bacterial L-ASNases, and focus on a detailed description of structure, function and clinical applications of these enzymes.

High chloroplast haplotype diversity in Greek populations of beech (Fagus sylvatica L.).

The distribution of chloroplast DNA (cpDNA) variations in Greek beech (Fagus sylvatica L.) populations was studied using chloroplast microsatellite markers. Thirteen haplotypes were identified from 40 populations by combining three different primers. Most of the cpDNA variation was distributed among populations, but a considerable variation was also observed within populations. The total diversity was very high for all regions. The N(st)/G(st) comparison was significant, indicating phylogenetic subdivision, but no strong spatial structure was detected, suggesting complex post-glacial migration patterns. Possible scenarios explaining this diversity pattern include the existence of several separated refugia in the region, the recolonisation of mountains by different beech lineages and the formation of an introgression zone between two different beech subspecies in the eastern part of the country.

Low back pain in schoolchildren: the role of mechanical and psychosocial factors.

BACKGROUND: Low back pain (LBP) in schoolchildren with no apparent clinical cause is known to be a common problem, but considerably less is understood regarding the aetiology of such pain. AIM: To assess the role of both mechanical and psychosocial factors (including emotional and behavioural problems and other somatic pain complaints) in childhood LBP. METHODS: A cross sectional study was carried out in a population of 1446 schoolchildren aged 11-14 years. Information on these potential risk factors for LBP was sought using a self complete questionnaire and a five day bag weight diary. RESULTS: Mechanical factors such as physical activity and school bag weight were not associated with LBP. However, strong associations with LBP were observed for emotional problems, conduct problems, troublesome headaches, abdominal pain, sore throats, and daytime tiredness. CONCLUSION: Results suggest that psychosocial factors rather than mechanical factors are more important in LBP occurring in young populations and could possibly be a reflection of distress in schoolchildren.

Chronic widespread pain in the population: a seven year follow up study.

OBJECTIVES: To document the natural course of chronic widespread pain (CWP) in a general population sample over a seven year period and to identify comorbidities which predict persistence. METHODS: A mailed survey questionnaire returned by 2334 adults registered with two general practices was used to obtain information on pain status (no pain, regional pain, or CWP) and other health and pain symptoms. Seven years later a second questionnaire was sent to responders who were still registered with the same general practice, asking about their current pain status. RESULTS: Information was obtained for 1386 adults (an adjusted response of 93%). The prevalence of CWP was similar for both surveys at 11% and 10% respectively. Of those with CWP initially, a third recorded CWP on the second survey and 15% were pain free. Only 2% of subjects with no initial pain had developed CWP at follow up. Of subjects with CWP on the initial survey who were aged over 50 years and reported dry eyes or mouth and daytime tiredness, 77% reported CWP seven years later. This contrasts with a persistence of only 9% for those aged under 50 and with neither symptom recorded at initial survey. CONCLUSION: The proportion of subjects from a general population sample changing from CWP to no pain, or vice versa, over a seven year period was very low. This suggests that pain, once established, is likely to persist (or recur) especially if accompanied by other somatic symptoms and older age.

Role of conserved residues in structure and stability: tryptophans of human serum retinol-binding protein, a model for the lipocalin superfamily.

Serum retinol binding protein (RBP) is a member of the lipocalin family, proteins with up-and-down beta-barrel folds, low levels of sequence identity, and diverse functions. Although tryptophan 24 of RBP is highly conserved among lipocalins, it does not play a direct role in activity. To determine if Trp24 and other conserved residues have roles in stability and/or folding, we investigated the effects of conservative substitutions for the four tryptophans and some adjacent residues on the structure, stability, and spectroscopic properties of apo-RBP. Crystal structures of recombinant human apo-RBP and of a mutant with substitutions for tryptophans 67 and 91 at 1.7 A and 2.0 A resolution, respectively, as well as stability measurements, indicate that these relatively exposed tryptophans have little influence on structure or stability. Although Trp105 is largely buried in the wall of the beta-barrel, it can be replaced with minor effects on stability to thermal and chemical unfolding. In contrast, substitutions of three different amino acids for Trp24 or replacement of Arg139, a conserved residue that interacts with Trp24, lead to similar large losses in stability and lower yields of native protein generated by in vitro folding. The results and the coordinated nature of natural substitutions at these sites support the idea that conserved residues in functionally divergent homologs have roles in stabilizing the native relative to misfolded structures. They also establish conditions for studies of the kinetics of folding and unfolding by identifying spectroscopic signals for monitoring the formation of different substructures.

Structural features of a zinc binding site in the superantigen strepococcal pyrogenic exotoxin A (SpeA1): implications for MHC class II recognition.

Streptococcal pyrogenic exotoxin A (SpeA) is produced by Streptococcus pyogenes, and has been associated with severe infections such as scarlet fever and Streptococcal Toxic Shock Syndrome (STSS). In this study, the crystal structure of SpeA1 (the product of speA allele 1) in the presence of 2.5 mM zinc was determined at 2.8 A resolution. The protein crystallizes in the orthorhombic space group P2(1)2(1)2, with four molecules in the crystallographic asymmetric unit. The final structure has a crystallographic R-factor of 21.4% for 7,031 protein atoms, 143 water molecules, and 4 zinc atoms (one zinc atom per molecule). Four protein ligands-Glu 33, Asp 77, His 106, and His 110-form a zinc binding site that is similar to the one observed in a related superantigen, staphylococcoal enterotoxin C2. Mutant toxin forms substituting Ala for each of the zinc binding residues were generated. The affinity of these mutants for zinc ion confirms the composition of this metal binding site. The implications of zinc binding to SpeA1 for MHC class II recognition are explored using a molecular modeling approach. The results indicate that, despite their common overall architecture, superantigens appear to have multiple ways of complex formation with MHC class II molecules.

Microbial superantigens: from structure to function.

Superantigens are highly potent immune stimulators with a unique ability to interact simultaneously with MHC class II molecules and T cell receptors, forming a trimolecular complex that induces profound T-cell proliferation and massive cytokine production. Recent structural studies have provided a wealth of information regarding these complex interactions, and it is now emerging that, despite their common 3-D architecture, superantigens are able to crosslink MHC class II molecules and T cell receptors in a variety of ways.

Structural similarities and differences in Staphylococcus aureus exfoliative toxins A and B as revealed by their crystal structures.

Staphylococcal aureus epidermolytic toxins (ETs) A and B are responsible for the induction of staphylococcal scalded skin syndrome, a disease of neonates and young children. The clinical features of this syndrome vary from localized blisters to severe exfoliation affecting most of the body surface. Comparison of the crystal structures of two subtypes of ETs-rETA (at 2.0 A resolution), rETB (at 2.8 A resolution), and an active site variant of rETA, Ser195Ala at 2.0 A resolution has demonstrated that their overall topology resembles that of a "trypsin-like" serine protease, but with significant differences at the N- and C-termini and loop regions. The details of the catalytic site in both ET structures are very similar to those in glutamate-specific serine proteases, suggesting a common catalytic mechanism. However, the "oxyanion hole," which is part of the catalytic sites of glutamate specific serine proteases, is in the closed or inactive conformation for rETA, yet in the open or active conformation for rETB. The ETs contain a unique amphipathic helix at the N-terminus, and it appears to be involved in optimizing the conformation of the catalytic site residues. Determination of the structure of the rETA catalytic site variant, Ser195Ala, showed no significant perturbation at the active site, establishing that the loss of biological and esterolytic activity can be attributed solely to disruption of the catalytic serine residue. Finally, the crystal structure of ETs, together with biochemical data and mutagenesis studies, strongly confirms the classification of these molecules as "serine proteases" rather than "superantigens."

Hospital referrals for low back pain: more coherence needed.

Low back pain is a common reason for hospital referral but little is known of the resulting workload in different specialties. All new outpatient attendances for conditions with low back pain were recorded over one month in a teaching hospital and a district general hospital. The patients were seen in at least ten specialties and two-fifths of them had been seen previously with the same symptom in another department. In the two hospitals, low back pain accounted for 15% and 12% of all new outpatient attendances. A more coherent referral policy is needed.

Development and validation of a questionnaire to assess disabling foot pain.

This study outlines the design and validation of a new self-administered instrument for assessing foot pain and disability. The 19-item questionnaire was tested on 45 rheumatology patients, 33 patients who had attended their general practitioner with a foot-related problem and 1000 responders to a population survey of foot disorders. Levels of reported disability were found to be greatest for rheumatology patients and least for community subjects. In addition, the instrument was able to detect differences in disability levels reported by community subjects who did and did not consult with a health care professional and those who did and did not have a history of past and current foot pain. A good level of agreement was found when items on the questionnaire were compared with similar items on the ambulation sub-scale of the Functional Limitation Profile questionnaire. A Cronbach's alpha value of 0.99 and item-total correlation values between 0.25 and 0.62 confirmed the internal consistency of the instrument. Finally the results of a principal components analysis identified three constructs that reflected disabilities that are associated with foot pain: functional limitation, pain intensity and personal appearance. The design of the foot disability questionnaire makes it a suitable instrument for assessing the impact of painful foot conditions in both community and clinical populations.

Short-term physical risk factors for new episodes of low back pain. Prospective evidence from the South Manchester Back Pain Study.

STUDY DESIGN: A prospective population-based cohort study performed in South Manchester, United Kingdom. OBJECTIVES: To determine whether nonoccupational physical activity and indicators of physical stress on the spine predict low back pain in the short term. SUMMARY OF BACKGROUND DATA: There is evidence that physical activity outside the workplace helps to protect against low back pain in the long term. However, such activity may injure or stress the spine in the short term. METHODS: A baseline survey questionnaire identified 2715 adults, aged 18-75 years, with no low back pain at the time of the survey. Information on potential predictors of low back pain also was obtained. New episodes of back pain were identified during the subsequent year. RESULTS: A new low back pain episode occurred in 34% of men and 37% of women. Poor general health at baseline was the strongest predictor of a new episode of pain (men: relative risk (RR) 1.5, 95% confidence intervals (CI) 0.8, 2.7; women: RR 2.2, 95% CI 1.2, 4.0). High weight was associated with subsequent low back pain in women (RR 1.4; 95% CI 1.0, 2.0), but neither height nor weight predicted low back pain in men. A self-rated low level of physical activity was not consistently linked with subsequent low back pain, nor were specific nonoccupational physical activities, apart from home-improvement work in men and regular sports in women. CONCLUSION: Although some specific activities may be hazardous to the back, physical activity outside the workplace does not increase the short-term risk of low back pain overall. Leisure-time physical activity is not a hazard to the back, whereas poor physical health in both genders and heavier weight in women do increase the risk of new low back pain episodes in the short term.

Predicting who develops chronic low back pain in primary care: a prospective study.

OBJECTIVES: To quantify the relative contribution of premorbid and episode specific factors in determining the long term persistence of disabling symptoms of low back pain. DESIGN: Prospective cohort study. SETTING: Two general practices in the south Manchester area. PARTICIPANTS: 180 patients, who previously participated in a cross sectional population survey, who consulted because of low back pain during the study period. They were followed at 1 week and 3 and 12 months after consultation. MAIN OUTCOME MEASURE: Persistent disabling low back pain in the 12 months after the consultation. RESULTS: Disabling low back pain persisted in one third of participants after consultation and was more common with increasing age, among those with a history of low back pain, and in women. Persistence of symptoms was associated with "premorbid" factors (high levels of psychological distress (odds ratio 3.3; 95% confidence interval 1.5 to 7.2), poor self rated health (3.6; 1.9 to 6.8), low levels of physical activity (2.8; 1.4 to 5.6), smoking (2. 1; 1.0 to 4.3), dissatisfaction with employment (2.4; 1.3 to 4.5)) and factors related to the episode of low back pain (duration of symptoms, pain radiating to the leg (2.6; 1.3 to 5.1), widespread pain (6.4; 2.7 to 15), and restriction in spinal mobility). A multivariate model based on six factors identified groups whose likelihood of persistent symptoms ranged from 6% to 70%. CONCLUSIONS: The presence of persistent low back pain is determined not only by clinical factors associated with pain but also by the premorbid state.

Predictors of early improvement in low back pain amongst consulters to general practice: the influence of pre-morbid and episode-related factors.

Low back pain symptoms are extremely common. affecting as many as 80% of the population at some time in their lives. However, the majority of the medical costs arise from the minority of patients whose symptoms become chronic. The authors propose a model in which chronicity is determined not only by factors related to the episode of low back pain, but also factors prior to the onset of symptoms (pre-morbid factors). No previous study has collected information on predictors of low back pain chronicity prior to the onset of symptoms. Participants in the South Manchester Low Back Pain Study, recruited by means of a cross-sectional population survey were followed prospectively over 18 months to identify those who consulted their general practitioner with a new episode of low back pain. At interview, 1-2 weeks post-consultation, it was determined whether or not subjects' symptoms had improved. In males, low levels of psychological distress, a higher than average reported level of physical activity, being in employment, and being satisfied with current work status were associated with a quick improvement in symptoms. In addition factors related to the episode, namely a short duration before consultation and symptoms with a sudden onset and confined to the lower back area, also strongly predicted a good early outcome. Using information on both pre-morbid and episode related factors, groups of male patients were identified whose probability of an early resolution of symptoms ranged between 0.25 and 1. Few factors, either pre-morbid or episode-related, were strongly associated with outcome amongst females. This large population-based study has shown, despite the known heterogeneity in the origin of low back pain and the pathologies associated with symptoms, an early improvement in symptoms amongst male attenders at general practice can be predicted on the basis of a small number of variables.

Chronic widespread pain in the community: the influence of psychological symptoms and mental disorder on healthcare seeking behavior.

OBJECTIVE: To determine whether psychological symptoms and mental disorder are an intrinsic part of the chronic widespread pain syndrome or whether they have been observed in clinic attenders primarily because of their influence on the decision to seek a medical consultation. METHODS: A population survey of 1953 subjects was conducted in the Greater Manchester area of the United Kingdom. The survey included a postal questionnaire, and in a subgroup of respondents with high levels of distress, the presence of mental disorder was assessed by a semistructured standardized interview. Subjects with chronic widespread pain were classified according to whether they had sought a medical consultation for the reported pain ("consulters") or not ("nonconsulters"). RESULTS: In all, 252 subjects (13%) satisfied American College of Rheumatology criteria for chronic widespread pain, and of these 72% reported having consulted a general practitioner about this pain. There was a clear difference in levels of psychological distress, measured by the General Health Questionnaire (GHQ), between consulters, nonconsulters, and those with no pain. Consulters did not differ from nonconsulters in terms of levels of fatigue, social dysfunction, or number of somatic symptoms reported. Although consulters (among whom one in 4 had a mental disorder) were more likely to have a mental disorder than subjects without pain [OR = 4.9, 95% CI (2.6, 9.5)] the increase in risk comparing consulters to nonconsulters [OR = 2.1, 95% CI (0.7, 5.9)] and nonconsulters to subjects without pain [OR = 1.4, 95% CI (0.7, 2.6)] was not significant. CONCLUSION: The results suggest that psychological distress is associated with chronic widespread pain in addition to any effect on whether consultation is sought for symptoms. The finding that one-quarter of consulters to primary care with chronic widespread pain have a mental disorder should alert primary care physicians and rheumatologists to screen for mental disorder in this group.

Structural basis for the recognition of superantigen streptococcal pyrogenic exotoxin A (SpeA1) by MHC class II molecules and T-cell receptors.

Streptococcal pyrogenic exotoxin A (SpeA) is a superantigen produced by Streptococcus pyogenes and is associated with severe infections characterized by rash, hypotension, multiorgan failure and a high mortality rate. In this study, an allelic form of this toxin, SpeA1, was crystallized with four molecules in the crystallographic asymmetric unit and its crystal structure was determined at 2.6 A resolution. The crystallographic R-factor was 19.4% (33 497 reflections) for 7031 protein atoms and 88 water molecules. The overall structure of SpeA1 is considerably similar to that of other prototype microbial superantigens, either of staphylococcal or streptococcal origin, but has greatest similarity to staphylococcal enterotoxin C (SEC). Based on structural and mutagenesis data, we have mapped several important residues on the toxin molecule, which are involved in the recognition of major histocompatibility complex (MHC) class II molecules and T-cell receptors. Also, the toxin appears to possess a potential zinc-binding site which may have implications in binding to particular MHC class II molecules. Finally, we propose models for SpeA1-MHC class II and SpeA1-T-cell receptor association and the relevance of this phenomenon to the superantigenic action of this toxin is considered.

Psychosocial risks for low back pain: are these related to work?

OBJECTIVES: To examine whether psychosocial risks for low back pain, reported in previous studies, are specific to the working population or are more widely relevant. METHODS: A large population-based survey identified subjects free of low back pain, and obtained information on the degree of satisfaction with work (or not working) and the adequacy of income for their family's needs. New episodes of consulting and non-consulting low back pain were identified prospectively over 12 months. The psychosocial risks for developing a new low back pain episode are examined in employed and non-employed groups separately. RESULTS: Dissatisfaction with work status doubled the risk of reporting a new low back pain episode in both the employed (odds ratio 2.0, 95% confidence intervals 1.2, 3.3) and non-employed (OR 2.0, 1.2, 3.1). Those perceiving their income as inadequate were at a threefold risk of consulting for this symptom regardless of their employment status (employed: OR 3.6, 1.8, 7.2; non-employed: OR 3.6, 1.4, 9.0). CONCLUSION: Psychosocial factors pose similar risks for a new low back pain episode in workers and the non-employed. This suggests that such influences may not be related solely to work but be a function of general aspects of life. The economic and individual impact of psychosocial interventions in the workplace, therefore, are likely to be limited unless account is taken of the influence of broader non-work related aspects.

Outcome of low back pain in general practice: a prospective study.

OBJECTIVES: To investigate the claim that 90% of episodes of low back pain that present to general practice have resolved within one month. DESIGN: Prospective study of all adults consulting in general practice because of low back pain over 12 months with follow up at 1 week, 3 months, and 12 months after consultation. SETTING: Two general practices in south Manchester. 490 subjects (203 men, 287 women) aged 18-75 years. MAIN OUTCOME MEASURES: Proportion of patients who have ceased to consult with low back pain after 3 months; proportion of patients who are free of pain and back related disability at 3 and 12 months. RESULTS: Annual cumulative consultation rate among adults in the practices was 6.4%. Of the 463 patients who consulted with a new episode of low back pain, 275 (59%) had only a single consultation, and 150 (32%) had repeat consultations confined to the 3 months after initial consultation. However, of those interviewed at 3 and 12 months follow up, only 39/188 (21%) and 42/170 (25%) respectively had completely recovered in terms of pain and disability. CONCLUSIONS: The results are consistent with the interpretation that 90% of patients with low back pain in primary care will have stopped consulting with symptoms within three months. However most will still be experiencing low back pain and related disability one year after consultation.

Crystal structure of microbial superantigen staphylococcal enterotoxin B at 1.5 A resolution: implications for superantigen recognition by MHC class II molecules and T-cell receptors.

Staphylococcal enterotoxin B is a member of a family of toxins known as superantigens that activate a large number of T-cells (up to 20%) by cross-linking MHC class II molecules with T-cell receptors in a Vbeta-restricted fashion. The crystal structure of staphylococcal enterotoxin B presented here has been determined at 1.5 A resolution, the highest resolution so far for a superantigen. The final model contains 1948 protein atoms and 177 water molecules and has excellent geometry with root-mean-square (rms) deviation of 0.007 A and 1.73 degrees in bond lengths and bond angles, respectively. The overall fold is similar to that of other microbial superantigens, but as it lacks the zinc-binding site found in other members of this family, such as staphylococcal enterotoxin A, C2 and D, this enterotoxin possesses only one MHC class II binding site. Comparison of the crystal structure of free SEB and in complex with an MHC class II molecule revealed no major changes in the MHC-binding site upon complex formation. However, a number of water molecules found in the free SEB may be displaced in the complex or contribute further to its stability. Detailed analysis of the TcR-binding site of SEB, SEA and SEC2 shows significant differences which may account for the ability of each superantigen to bind specific Vbeta sequences.