Pre-admission ambient air pollution and blood soot particles predict hospitalisation outcomes in COVID-19 patients

BACKGROUND

Air pollution exposure is one of the major risk factors for aggravation of respiratory diseases. We investigated whether exposure to air pollution and accumulated black carbon (BC) particles in blood were associated with coronavirus disease 2019 (COVID-19) disease severity, including the risk for intensive care unit (ICU) admission and duration of hospitalisation.

METHODS

From May 2020 until March 2021, 328 hospitalised COVID-19 patients (29% at intensive care) were recruited from two hospitals in Belgium. Daily exposure levels (from 2016 to 2019) for particulate matter with aerodynamic diameter <2.5 µm and <10 µm (PM2.5 and PM10, respectively), nitrogen dioxide (NO2) and BC were modelled using a high-resolution spatiotemporal model. Blood BC particles (internal exposure to nano-sized particles) were quantified using pulsed laser illumination. Primary clinical parameters and outcomes included duration of hospitalisation and risk of ICU admission.

RESULTS

Independent of potential confounders, an interquartile range (IQR) increase in exposure in the week before admission was associated with increased duration of hospitalisation (PM2.5 +4.13 (95% CI 0.74-7.53) days, PM10 +4.04 (95% CI 1.24-6.83) days and NO2 +4.54 (95% CI 1.53-7.54) days); similar effects were observed for long-term NO2 and BC exposure on hospitalisation duration. These effect sizes for an IQR increase in air pollution on hospitalisation duration were equivalent to the effect of a 10-year increase in age on hospitalisation duration. Furthermore, for an IQR higher blood BC load, the OR for ICU admission was 1.33 (95% CI 1.07-1.65).

CONCLUSIONS

In hospitalised COVID-19 patients, higher pre-admission ambient air pollution and blood BC levels predicted adverse outcomes. Our findings imply that air pollution exposure influences COVID-19 severity and therefore the burden on medical care systems during the COVID-19 pandemic.

Residential green space is associated with a buffering effect on stress responses during the COVID-19 pandemic in mothers of young children, a prospective study

Green spaces are associated with increased well-being and reduced risk of developing psychiatric disorders. In this study, we aimed to investigate how residential proximity to green spaces was associated with stress response buffering during the COVID-19 pandemic in a prospective cohort of young mothers. We collected information on stress in 766 mothers (mean age: 36.6 years) from the ENVIRONAGE birth cohort at baseline of the study (from 2010 onwards), and during the COVID-19 pandemic (from December 2020 until May 2021). Self-reported stress responses due to the COVID-19 pandemic were the outcome measure. Green space was quantified in several radiuses around the residence based on high-resolution (1 m²) data. Using ordinal logistic regression, we estimated the odds of better resistance to reported stress, while controlling for age, socio-economic status, stress related to care for children, urbanicity, and household change in income during the pandemic. In sensitivity analyses we corrected for pre-pandemic stress levels, BMI, physical activity, and changes in health-related habits during the pandemic. We found that for an inter-quartile range contrast in residential green space 300 m and 500 m around the residence, participants were respectively 24% (OR = 1.24, 95%CI: 1.03 to 1.51) and 29% (OR = 1.29, 95%CI: 1.04 to 1.60) more likely to be in a more resistant category, independent of the aforementioned factors. These results remained robust after additionally controlling for pre-pandemic stress levels, BMI, physical activity, smoking status, urbanicity, psychological disorders, and changes in health-related habits during the pandemic. This prospective study in young mothers highlights the importance of proximity to green spaces, especially during challenging times.

Higher surrounding green space is associated with better attention in Flemish adolescents

INTRODUCTION

Previous studies suggested that green space is beneficial for the cognitive development in children. However, evidence in adolescents is limited. Therefore, we aim to investigate green space exposure in association with attention and behaviour in adolescents.

METHODS

This study includes 596 Flemish adolescents between 13 and 17 years old. Attention was assessed with Stroop Test (selective attention) and Continuous Performance Test (sustained and selective attention). Behaviour was determined based on the Strengths and Difficulties Questionnaire. Green space was estimated in several radius distances around their current residence and school based on high-resolution land cover data. Multilevel regression analyses were used adjusting for participant's age, sex, education level of the mother, and area deprivation index.

RESULTS

Surrounding green space in a 2000 m radius is associated with a faster reaction time in adolescents. An IQR (13%) increment in total green space within 2000 m of the residence and school combined, is associated with a 32.7 ms (95% CI: -58.9 to -6.5; p = 0.02) and a 7.28 ms (95% CI: -11.7 to -2.8; p = 0.001) shorter mean reaction time between the presentation of a stimulus and the response based on the Stroop Test and the Continuous Performance Test. Subdividing green space based on vegetation height, shows that green space higher than 3 m is associated with a faster reaction time of the Continuous Performance Test (-6.50 ms; 95% CI: -10.9 to -2.2; p = 0.004), while low green is not. We did not find an association between green space and behavioural development in adolescents.

CONCLUSIONS

Our study shows that green space, especially trees, surrounding the residence and school combined is associated with better sustained and selected attention in adolescents. These findings indicate that the availability of green is important for adolescents that are growing up in a rapidly urbanizing world.

Determinants of Chronic Biological Stress, Measured as Hair Cortisol Concentration, in a General Population of Adolescents: From Individual and Household Characteristics to Neighborhood Urbanicity

Chronic biological stress may adversely affect adolescents' physical and mental health, but insight in the personal and environmental factors that determine chronic stress is limited. We measured 3-month cumulative hair cortisol concentration (HCC) in 419 adolescents, participating in the Flemish Environment and Health Study. Adolescents' health and lifestyle characteristics, household and neighborhood socio-economic status as well as neighborhood urbanicity were assessed as potential determinants of HCC, using multiple linear regression models. We additionally explored heterogeneity of our results by sex. HCC were significantly higher in boys from densely populated neighborhoods, the association was not significant in girls. Accordingly, boys living outside cities had significantly lower HCC than boys, living in cities. HCC was significantly lower in adolescents with an optimal vitality, a measure of a positive mental health status. In adolescent girls, menarcheal status (pre-/postmenarche) was a significant determinant of HCC. Our findings are the first to suggest that residential urbanicity may have an impact on chronic biological stress in a general population of adolescent boys.

Urinary Polycyclic Aromatic Hydrocarbon Metabolites Are Associated with Biomarkers of Chronic Endocrine Stress, Oxidative Stress, and Inflammation in Adolescents: FLEHS-4 (2016-2020)

Polycyclic aromatic hydrocarbons (PAHs) are environmental pollutants of public health concern. Multiple biological mechanisms have been hypothesized to contribute to PAHs-associated adverse health effects. Little is known about the impact of PAHs on endocrine stress and inflammation in adolescence. We examined 393 Flemish adolescents (14-15 years) cross-sectionally, measured urinary concentrations of hydroxylated naphthalene, fluorene, phenanthrene and pyrene metabolites, and calculated the sum of all measured metabolites. We determined hair cortisol concentration (HCC) as endocrine stress biomarker, leucocyte counts and neutrophil-lymphocyte ratio (NLR) in peripheral blood as inflammatory biomarkers, and urinary 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG) concentration as oxidative stress biomarker. Exposure-response associations were analyzed by multiple regression, adjusted for a priori selected covariates. A doubling of 1-hydroxypyrene concentration was associated with a factor of 1.13 (95% CI: 1.03, 1.24) increase in HCC and a factor of 1.07 (95% CI: 1.02, 1.13) increase in 8-oxodG. Doublings of 2- and 3-hydroxyphenanthrene concentrations were associated with a factor of 1.08 (95% CI: 1.02, 1.14) and 1.06 (95% CI: 1.00, 1.12) increase in 8-oxodG, respectively. Doubling of 2-hydroxyphenanthrene and of the sum of 2- and 3-hydroxyfluorene was associated with, respectively, a factor of 1.08 (95% CI: 1.02, 1.14) and 1.06 (95% CI: 1.01, 1.13) increase in NLR. Our results indicate the glucocorticoid pathway as a potential target for PAH exposure in adolescents and suggest oxidative stress, endocrine stress, and inflammation in adolescence as underlying mechanisms and early markers for PAH-related adverse health effects.

Long-term residential exposure to air pollution is associated with hair cortisol concentration and differential leucocyte count in Flemish adolescent boys

BACKGROUND

Exposure to air pollution and traffic noise are associated with adverse health outcomes in adolescents. Chronic endocrine stress and systemic inflammation have been hypothesized to underlie the adverse health effects. Simultaneous assessment of inflammation and chronic endocrine stress in epidemiological studies is lacking. The aim of the study was to investigate biomarkers of chronic endocrine stress and inflammation in relation to long-term residential exposure to air pollution and traffic noise in adolescents.

METHODS

In Flemish adolescents (14-15 years), we determined hair cortisol concentration (HCC) as a chronic stress biomarker in 3-cm scalp-near hair sections (n = 395), and leucocyte and leucocyte subtype counts (neutrophils, monocytes, lymphocytes) as inflammatory biomarkers in peripheral blood (n = 385). Daily particulate matter (PM_2.5, PM₁₀), nitrogen dioxide (NO₂) and black carbon (BC) concentrations were modelled at the residential address and averaged over 3-month and 1-year periods prior to sampling. Residential traffic noise level was estimated and classified in 5 dB intervals. Sex-specific associations between residential exposures and effect biomarkers were studied using linear regression models, adjusted for a priori selected covariates.

RESULTS

In boys, HCC increased with a factor 1.30 (95% CI: 1.10, 1.54) for an increase in 1-year mean NO₂ from the 25th to 75th percentile (p75/p25), after adjustment for age, BMI, personal and neighborhood socioeconomic status. The corresponding estimate for PM₁₀ was 1.24 (95% CI: 1.02, 1.51). Total leucocyte count in boys, adjusted for the aforementioned covariates and recent health complaints, was positively associated with PM_2.5, PM₁₀, NO₂ and BC. In particular, the neutrophil count increased with a factor 1.11 (95% CI: 1.03, 1.19) for a (p75/p25)-factor increase in 1-year mean BC, corresponding estimates for PM_2.5, PM₁₀ and NO₂ were 1.10 (95% CI: 1.01, 1.19), 1.10 (95% CI: 1.01, 1.20) and 1.08 (95% CI: 1.00, 1.16). Lymphocyte count increased with a factor 1.05 (95% CI: 1.01, 1.10) for a (p75/p25)-factor increase in 1-year mean NO₂. Similar results were observed for 3-month mean exposures. Results were robust to adjustment for recent air pollution exposure. In girls, air pollutants were not associated with HCC or differential leucocyte count. Residential traffic noise level was not associated with HCC or leucocyte counts in boys nor girls.

CONCLUSIONS

Long-term residential exposure to air pollutants was positively associated with chronic endocrine stress and inflammation in adolescent boys, not in girls. This study may contribute to a better understanding of the early pathophysiological changes that may underlie adverse health effects of air pollution exposure in adolescents.

Mitochondrial DNA methylation in placental tissue: a proof of concept study by means of prenatal environmental stressors

While previous studies have demonstrated that prenatal exposure to environmental stressors is associated with mitochondrial DNA (mtDNA) methylation, more recent investigations are questioning the accuracy of the methylation assessment and its biological relevance. In this study, we investigated placental mtDNA methylation while accounting for methodological issues such as nuclear contamination, bisulphite conversion, and PCR bias. From the ENVIRONAGE birth cohort, we selected three groups of participants (n = 20/group). One group with mothers who smoked during pregnancy (average 13.2 cig/day), one group with high air pollutant exposure (PM_2.5: 16.0 ± 1.4 µg/m³, black carbon: 1.8 ± 0.3 µg/m³) and one control group (non-smokers, PM_2.5: 10.6 ± 1.7 µg/m³, black carbon: 0.9 ± 0.1 µg/m³) with low air pollutant exposure. DNA methylation levels were quantified in two regions of the displacement loop control region (D-loop and LDLR2) by bisulphite pyrosequencing. Additionally, we measured DNA methylation on nuclear genes involved in mitochondrial maintenance (PINK1, DNA2, and POLG1) and assessed mtDNA content using qPCR. Absolute D-loop methylation levels were higher for mothers that smoked extensively (+0.36%, 95% CI: 0.06% to 0.66%), and for mothers that were highly exposed to air pollutants (+0.47%, 95% CI: 0.20% to 0.73%). The relevance of our findings is further supported, as D-loop methylation levels were correlated with placental mtDNA content (r = −0.40, p = 0.002) and associated with birth weight (−106.98 g, 95% CI: −209.60 g to −4.36 g for an IQR increase in D-loop methylation). Most notably, our data demonstrates relevant levels of mtDNA methylation in placenta tissue, with significant associations between prenatal exposure to environmental stressors and D-loop methylation.

Does Social Capital Benefit Older Adults' Health and Well-Being? The Mediating Role of Physical Activity

Objectives: To assess whether social capital benefits older adults' self-rated health and well-being and whether physical activity mediates this relation. Methods: A survey study was conducted among members of a sociocultural organization (age ≥55 years), both cross-sectionally (baseline Time 1; N = 959) and longitudinally (3-year follow-up Time 2; N = 409). Results: Specific indicators of social capital were positively, though modestly, related to health and well-being at Time 1 and Time 2. Experienced connectedness with age peers emerged as the strongest predictor. Physical activity only mediated the relation with experienced safety in society. Discussion: The relative importance of older adults' experienced connectedness with their age peers underlines the importance of internalized group membership as a determinant of their health and well-being. Physical activity seems to play only a minor mediating role.

P35 Ability to quantify stereoelectroencephalography (SEEG) electrode trajectory proximity to vessels across imaging protocols

Objectives

Automated planning of stereoelectroencephalography (SEEG) electrode trajectories is dependent on vessel segmentation.1 We quantify imaging protocols ability to measure trajectory-to-vessel distance.

Design

Retrospective analysis.

Subjects

Ten consecutive patients were selected whom had SEEG implantation (95 electrodes) and Digital Catheter Subtraction Angiography (DSA) with catheterization of carotid or vertebral arteries, post-gadolinium T1-weighted (GAD), phase-contrast MR angiography and MR venography (MR) acquired.

Methods

SEEG trajectories were planned manually with DSA. Minimum distance to vessels and risk1 were computed for each trajectory using vessel segmentation from GAD, MR, or DSA. Vessel size was considered by including DSA vessels diameters above 1, 2, 3, or 4 mm.

Results

Minimum distance to a vessel was 6.2±3.9 mm (GAD), 2.5±1.6 mm (MR), and 1.5±1.2 mm (DSA). Based on DSA vessel size minimum distances were 2.0±1.5 mm (DSA >1 mm), 3.4±2.6 (DSA >2 mm), 6.6±4.6 mm (DSA >3 mm), and 11.8±7.9 mm (DSA >4 mm). Risk was 0.4±0.4 (GAD), 0.8±0.4 (MR), and 1.1±0.2 (all DSA), 1.0±0.2 (DSA >1 mm), 0.7±0.4 (DSA >2 mm), 0.4±0.5 (DSA >3 mm), and 0.2±0.3 (DSA >4 mm).

Conclusions

DSA is best able to segment vessels. MR has metrics similar to DSA vessels above 2 mm. GAD has metrics similar to DSA vessels above 3 mm.

Variety in diagnosis and treatment of periprosthetic joint infections in Belgium and the Netherlands

Recently, guidelines regarding diagnosis and treatment of periprosthetic joint infection (PJI) have been published, but it is unknown how well these are -followed in the Netherlands and Belgium. Therefore, a survey study was performed in the Netherlands and Belgium. 81 orthopedic departments responded (54% in the Netherlands, 52% in Belgium). The majority used protocols for antibiotic and surgical treatment. To discriminate between early and late infection, differences in periods used were seen between respondents, and between countries. Empirical antibiotic treatment varied greatly. Debridement, antibiotics, irrigation and retention of the prosthesis (DAIR) is the -almost unanimous treatment of choice for early PJI. Guidelines are available, but seem not (yet) to be -followed accurately, and do not have answers to all possible treatment options. Perhaps, national guidelines might produce more standardized care, and -consequentially, easier comparison for research, more transparency for patients, and less health care costs.

Direct anterior approach versus posterolateral approach in total hip arthroplasty : one surgeon, two approaches

Early research shows several advantages of the Direct Anterior Approach (DAA) in total hip arthroplasty (THA), although no studies evaluated the DAA on a regular operating table without using fluoroscopy. We performed a retrospective cohort study on the outcome of this variation of the DAA compared with the posterolateral approach (PLA) with one year follow-up. All procedures were uncemented THA performed in 2012 by a single surgeon. Patients in the DAA group (N = 45) had a lower Body Mass Index (p > .001) than the PLA group (N = 38). Functional outcome, pain scores and complications were comparable between the two approaches. Compared with PLA, the DAA was associated with longer operation time (p > 0.001), more blood loss (p > 0.001), shorter length of stay (p = .009), and more adequate acetabular cup inclination (p = .004). This study shows that the DAA on a regular operating table without using fluoroscopy has several advantages compared to the PLA.

Abstract P5-01-06: Differences in FGF1 and FGFR2 expression in BRCA1-associated, BRCA2-associated, and sporadic breast carcinomas

Introduction. In contrast to BRCA1-associated breast cancer, a distinctive phenotype for BRCA2-associated carcinomas has not been identified yet as there is no clear distinction between BRCA2- and non-BRCA mutation related or sporadic carcinomas. Recently, studies suggest overexpression of fibroblast growth factor 1 (FGF1) and fibroblast growth factor receptor 2 (FGFR2) in BRCA2 related cancers. The aim of the study was therefore to investigate whether there is differential expression of FGF1 and/or FGFR2 between BRCA2 related and sporadic and BRCA1 related cancers. This would reveal the usefulness of FGF1 and FGFR2 immunohistochemistry in daily pathology practise.

Method. Invasive breast carcinomas of 33 BRCA1 and 22 BRCA2 germline mutation carriers and a tissue microarray containing 104 sporadic invasive breast carcinomas were immunohistochemically stained for FGF1, FGFR2, estrogen receptor (ER), progesterone receptor (PR), HER2, epidermal growth factor receptor 1 (EGFR), cytokeratin (CK) 5/6 and CK14.

Results. FGFR2 expression was seen in 68.2% and 79.0% of BRCA2-associated and sporadic carcinomas respectively, in contrast to 22.6% of BRCA1-associated tumors (p = 0.000). FGF1 expression was seen in 72.7% of BRCA2-associated carcinomas and in 45.2% and 41.8% in BRCA1-associated and sporadic carcinomas, respectively (p = 0.032).

Conclusion. FGFR2 expression differs significantly between BRCA1- and BRCA2 associated breast carcinomas but not between BRCA2 and sporadic cancers. FGF1 expression differs significantly between BRCA2-associated and sporadic carcinomas and could be used as a BRCA2-specific biomarker.

Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr P5-01-06.

Quality of life with heart failure: psychosocial determinants to be considered by cardiologists

BACKGROUND

Independent determinants of QOL (quality of life) with heart disease have been recognised and include factors such as severity of medical condition, comorbidity, and concomitant medication. Psychosocial factors, as 'ability to cope with the unpleasantness of the medical condition', 'want of information', and 'social identification' have an important influence on self-perceived wellbeing, but their influence on health-related QOL domains and self-perceived QOL in patients with heart failure has not been systematically studied.

OBJECTIVE

To assess correlation between such psychosocial factors and QOL in patients with heart failure.

METHODS

Patients from the outpatient heart failure clinic of the Martini Hospital, a 1000-bed community hospital in the city of Groningen, the Netherlands, were included if their ejection fractions were <40% and their medical diagnosis according to their cardiologists was stable chronic congestive heart failure. The following QOL estimators were applied: Pearlin's Mastery Scale, Stewart's Short Form 36 Quality of Life Questionnaire, Dupuy's Index of Wellbeing, Cantrill's Self-perceived Quality of Life Scale, Mester's Want of Information Scale. Internal consistency of the multi-item scales was estimated by Cronbach's alphas. Linear and multiple linear regression analyses were performed of the data.

RESULTS

Sixty patients were enrolled, 41 males and 19 females, average age 68 years (range 51 to 84 years). 'Ability to cope with the unpleasantness of the medical condition' was not only an independent determinant of self-perceived and health-related QOL (both p<0.001), but also of each domain of health-related QOL separately (p<0.001 for each domain). Lack of 'adequate medical information' and 'negative social identification' (identification with fellow-sufferers who are doing worse) were negative predictors of 'ability to cope' (p<0.01 and <0.001 respectively). 'Negative social identification' was also an independent determinant of self-perceived QOL, both unadjusted and after adjustment for 'ability to cope' and 'adequate medical information'.

CONCLUSION

Relevant recommendations from this paper to be considered by cardiologists during everyday office hours could include: 1. Patients who express having difficulties in coping with the unpleasant aspects of their underlying heart condition have low health-related QOL as well as low self-perceived QOL. 2. Providing adequate medical information is a significant contributor to both better 'ability to cope' and better self-perceived QOL. 3. Avoiding identifying with fellow-sufferers who are doing worse and, instead, starting to identify with those who are doing better, are significant contributors to both better 'ability to cope' and better self-perceived QOL.

Baccatin III induces assembly of purified tubulin into long microtubules

Baccatin III is widely considered to be an inactive derivative of Taxol. We have reexamined its effect on in vitro assembly of tubulin under a variety of conditions. We found baccatin III to be active in all circumstances in which Taxol is active: it assembled GTP-tubulin, GDP-tubulin, and microtubule protein into normal microtubules and stabilized these polymers against cold-induced disassembly. The effect of baccatin III on in vitro microtubule assembly was quantitatively assessed through determination of critical concentrations, which can be used to obtain the apparent equilibrium constants for the addition of tubulin subunits to growing microtubules. The apparent equilibrium constants for the growth reaction for baccatin III-induced GTP-tubulin and GDP-tubulin assembly measured at 37 degrees C were 4.2-4.6-fold less than those measured for Taxol-induced GTP-tubulin and GDP-tubulin assembly. These data indicate that the entire Taxol side chain contributes only about -1 kcal/mol to the apparent standard free energy of microtubule growth at 37 degrees C regardless of the nature of the E site nucleotide. These data also support the idea that the majority of the interactions between Taxol and tubulin that affect this equilibrium occur between the baccatin portion of the molecule and the binding site. We have also observed a structural difference in microtubules formed using baccatin III and Taxol. Baccatin III-induced microtubules were routinely much longer than those assembled by Taxol, even when very high concentrations of baccatin III were employed. One interpretation of these data is that baccatin III and Taxol differ in their abilities to nucleate GTP-tubulin. This difference in activity may have bearing on the large disparity in cytotoxicity of the two molecules.

Structures of free and complexed forms of Escherichia coli xanthine-guanine phosphoribosyltransferase

Structures of free, substrate-bound and product-bound forms of Escherichia coli xanthine-guanine phosphoribosyltransferase (XGPRT) have been determined by X-ray crystallography. These are compared with the previously determined structure of magnesium and sulphate-bound XPRT. The structure of free XGPRT at 2.25 A resolution confirms the flexibility of residues in and around a mobile loop identified in other PRTases and shows that the cis-peptide conformation of Arg37 at the active site is maintained in the absence of bound ligands. The structures of XGPRT complexed with the purine base substrates guanine or xanthine in combination with cPRib-PP, an analog of the second substrate PRib-PP, have been solved to 2.0 A resolution. In these two structures the disordered phosphate-binding loop of uncomplexed XGPRT becomes ordered through interactions with the 5'-phosphate group of cPRib-PP. The cyclopentane ring of cPRib-PP has the C3 exo pucker conformation, stabilised by the cPRib-PP-bound Mg2+. The purine base specificity of XGPRT appears to be due to water-mediated interactions between the 2-exocyclic groups of guanine or xanthine and side-chains of Glu136 and Asp140, as well as the main-chain oxygen atom of Ile135. Asp92, together with Lys115, could help stabilise the N7-protonated tautomer of the incoming base and could act as a general base to remove the proton from N7 when the nucleotide product is formed. The 2.6 A resolution structure of XGPRT complexed with product GMP is similar to the substrate-bound complexes. However, the ribose ring of GMP is rotated by approximately 24 degrees compared with the equivalent ring in cPRib-PP. This rotation results in the loss of all interactions between the ribosyl group and the enzyme in the product complex.

Smoking and schizophrenia

Individuals with schizophrenia have a high prevalence of smoking compared with the general population and little is known about why so many people with schizophrenia smoke. This paper reviews suggestions of differences in motivation for smoking. Possible explanations for smoking include psychological reasons, together with possible effects on positive and negative symptoms of schizophrenia and reduced side-effects of neuroleptics. Understanding complex issues related to smoking and schizophrenia is important prior to developing health promotion strategies.

Crystal structure of Escherichia coli xanthine phosphoribosyltransferase

Xanthine phosphoribosyltransferase (XPRT; EC 2.4.2.22) from Escherichia coli is a tetrameric enzyme having 152 residues per subunit. XPRT catalyzes the transfer of the phosphoribosyl group from 5-phospho-alpha-D-ribosyl 1-pyrophosphate (PRib-PP) to the 6-oxopurine bases guanine, xanthine, and hypoxanthine to form GMP, XMP, and IMP, respectively. Crystals grown in the absence of substrate or product were used to determine the structure of XPRT at a resolution of 1.8 A, by multiple isomorphous replacement. The core structure of XPRT includes a five-stranded parallel beta-sheet surrounded by three alpha-helices, which is similar to that observed in other known phosphoribosyltransferase (PRTase) structures. The XPRT structure also has several interesting features. A glutamine residue in the purine binding site may be responsible for the altered 6-oxopurine base specificity seen in this enzyme compared to other 6-oxopurine PRTases. Also, we observe both a magnesium ion and a sulfate ion bound at the PRib-PP binding site of XPRT. The sulfate ion interacts with Arg-37 which has a cis-peptide conformation, and the magnesium ion interacts with Asp-89, a highly conserved acidic residue in the PRib-PP binding site motif. The XPRT structure also incorporates a feature which has not been observed in other PRTase structures. The C-terminal 12 residues of XPRT adopt an unusual extended conformation and make interactions with a neighboring subunit. The very last residue, Arg-152, could form part of the active site of a symmetry-related subunit in the XPRT tetramer.

Crystallization and preliminary X-ray crystallographic studies of Escherichia coli xanthine phosphoribosyltransferase

Xanthine phosphoribosyltransferase (XPRT; EC 2.4.2.22) from Escherichia coli is a purine salvage enzyme which synthesizes the nucleotides GMP, XMP, and IMP. A mutant C59A, which is more stable than wild-type XPRT while retaining high activity, has been prepared and crystallized to give three different crystal forms (A, B, and C). Form A crystals are orthorhombic (P21212), with unit cell dimensions a = 59.2 A, b = 92.9 A, c = 53.2 A. Form B crystals are monoclinic (C2) with unit cell dimensions a = 84.4 A, b = 70.8 A, c = 54.1 A, and beta = 113.4 degrees, and form C crystals are tetragonal (P41212 or P43212) with unit cell dimensions a,b = 94 A, c = 167.5 A. Wild-type XPRT and a selenomethionine derivative of C59A XPRT have also been crystallized in the orthorhombic form. The selenomethionine derivative was prepared by expressing XPRT in the usual E. coli strain without the need for a methionine auxotroph. Cells were grown in a methionine-deficient medium supplemented with selenomethionine which gave >95% incorporation. Both the wild-type and selenomethionine C59A XPRT crystals are isomorphous with C59A form A crystals.