Care seeking for childhood illnesses in rural Mtwara, south-east Tanzania: a mixed methods study

BACKGROUND

Care seeking was assessed in preparation for a study of the health impact of novel design houses in rural Mtwara, Tanzania.

METHODS

A total of 578 residents of 60 villages participated in this mixed-methods study from April to August 2020. Among them, 550 participated in a healthcare-seeking survey, 17 in in-depth interviews and 28 in key informant interviews.

RESULTS

The decision to seek care was based on symptom severity (95.4% [370]). Caregivers first visited non-allopathic healthcare providers or were treated at home, which led to delays in seeking care at healthcare facilities. More than one-third (36.0% [140]) of respondents took >12 h seeking care at healthcare facilities. The majority (73.0% [282]) visited healthcare facilities, whereas around one-fifth (21.0% [80]) sought care at drug stores. Treatment costs deterred respondents from visiting healthcare facilities (61.4% [338]). Only 10 (3.6%) of the households surveyed reported that they were covered by health insurance.

CONCLUSIONS

Quality of care, related to institutional factors, impacts timely care seeking for childhood illnesses in Mtwara, Tanzania. Ensuring accessibility of facilities is therefore not sufficient.

Understanding reticence to occupy free, novel-design homes: A qualitative study in Mtwara, Southeast Tanzania

INTRODUCTION

The population of Africa set to reach 2 billion by 2050. There is therefore great demand for housing across the continent. Research on modified novel designs for housing is a priority to ensure that these homes are not sites of infection for diseases transmission such as malaria. One trial to assess the protection afforded by novel design houses is underway in Mtwara Region, southeastern Tanzania. After constructing 110 of such homes across 60 villages, project staff encountered a certain reticence of the target population to occupy the homes and were faced with accusations of having nefarious intentions. This article explores these accusations, their impacts on home occupancy and lessons for future housing studies.

METHODS

This qualitative study drew on in-depth interviews and focus group discussions with ten occupants of the intervention homes, six community leaders and a further 24 community members. Interviews were recorded, transcribed verbatim and translated to English for qualitative content analysis.

RESULTS

In communities around the Star Homes, during construction and handover, project staff were widely associated with 'Freemasons', a term used to practices, secrecy, and other conspiracy theories in rural Tanzania. These connections were attributed to other community members and explained in terms of knowledge deficit or envy, with others hoping to be allocated the home. The stories were embedded in assumptions of reciprocity and suspicions about study motives, linked to limited experience of research. The relationship between the accusations of freemasonry and reticence to occupy the houses was not straightforward, with project staff or relatives playing a role in decisions. The stakes were high, because the recipients of Star Homes were the poorest families in targeted communities.

CONCLUSION

The results indicate the need for long-term and proactive community engagement, which focuses on building relationships and providing information through recognizable voices and formats. Given the stakes at play in housing interventions, research teams should be prepared for the social upheaval the provision of free new housing can cause.

Studying the health benefits of improved housing in rural Tanzania: challenges and progress

Millions of affordable healthy homes are needed for the rapidly expanding population of sub-Saharan Africa. This enormous challenge is an opportunity to address pervasive health issues linked to housing, where diseases that most impact children-malaria, diarrhoea and respiratory tract infections-are often acquired. A pilot project in northern Tanzania demonstrated the potential of novel house designs to reduce infectious disease transmission in homes. To conduct a randomized controlled trial of one novel-design house, the research team moved to the southeast of the country. This article describes the challenges experienced during the construction and initial evaluation of the novel house.

House screening for malaria control: views and experiences of participants in the RooPfs trial

BACKGROUND

The housing stock of rural sub-Saharan Africa is changing rapidly. With millions of new homes required over the coming decades, there is an opportunity to protect residents by screening homes from malaria mosquitoes. This study, undertaken in the Upper River Region of The Gambia, explores local perceptions of what a good house should provide for its inhabitants and responses to living in a house that has been modified as part of a randomized control trial designed to assess whether improved housing provided additional protection against clinical malaria in children (the RooPfs trial).

METHODS

This descriptive, exploratory study was undertaken over 22 months using mixed-methods (informal conversations, observations, focus group discussions, photovoice, and a questionnaire survey) in a parallel convergent design. Analysis was conducted across the data sets using a framework approach. Following coding, the textual data were charted by a priori and emerging themes. These themes were compared with the quantitative survey results. The nature and range of views about housing and the RooPfs study modifications and the relationships among them were identified and described.

RESULTS

The data were derived from a total of 35 sets of observations and informal conversations in 10 villages, 12 discussions with the photovoice photographers, 26 focus group discussions (across 13 villages) and 391 completed questionnaires. The study participants described a 'good house' as one with a corrugate-metal roof, cement walls (preferably cement block, but mud block covered with cement plaster was also an acceptable and cheaper substitute) and well-fitting doors. These features align with local perceptions of a modern house that provides social status and protection from physical harms. The RooPfs modifications were largely appreciated, although poor workmanship caused concerns that houses had become insecure. However, the long-term trusting relationship with the implementing institution and the actions taken to rectify problems provided reassurance and enhanced acceptability.

CONCLUSION

In developing housing to address population needs in Africa, attention should be paid to local perceptions of what is required to make a house secure for its inhabitants, as well as providing a healthy environment.

Assessing the impact of a novel house design on the incidence of malaria in children in rural Africa: study protocol for a household-cluster randomized controlled superiority trial

Background

Traditional rural housing in hot, humid regions of sub-Saharan Africa usually consists of single-level, poorly ventilated dwellings. Houses are mostly poorly screened against malaria mosquitoes and limited airflow discourages the use of bednets resulting in high indoor transmission. This study aims to determine whether living in a novel design house with elevated bedrooms and permeable screened walls reduces malaria, respiratory tract infections, and diarrhoea among children in rural Tanzania.

Methods/study design

This is a household-randomized, controlled study in 60 villages in Mtwara, Tanzania. A total of 550 households are randomly selected, 110 of which are allocated a novel design house and 440 households continue to reside in traditional houses. A dynamic cohort of about 1650 children under 13 years will be enrolled and followed for 3 years, approximately 330 living in novel design houses and 1320 in traditional rural houses. The primary endpoint is the incidence of malaria; secondary endpoints are incidences of acute respiratory tract infections and diarrhoea diseases detected by passive and active surveillance. Exposure to malaria vectors will be assessed using light traps in all study houses. Structural, economic, and social science studies will assess the durability, cost-effectiveness, and acceptability of the new houses compared with traditional housing. Environmental data will be collected indoors and outdoors in study homes to assess the differences between house typologies.

Discussion

This is the first randomized controlled trial to assess the protective efficacy of a new house design targeting malaria in sub-Saharan Africa. The findings of this study could influence the future construction of homes in hot and humid zones of Africa.

Trial registration

ClinicalTrials.govNCT04529434. Registered on August 27, 2020

The effect of light and ventilation on house entry by Anopheles arabiensis sampled using light traps in Tanzania: an experimental hut study

Background

In sub-Saharan Africa, house design and ventilation affects the number of malaria mosquito vectors entering houses. This study hypothesized that indoor light from a CDC-light trap, visible from outside a hut, would increase entry of Anopheles arabiensis, an important malaria vector, and examined whether ventilation modifies this effect.

Methods

Four inhabited experimental huts, each situated within a large chamber, were used to assess how light and ventilation affect the number of hut-entering mosquitoes in Tanzania. Each night, 300 female laboratory-reared An. arabiensis were released inside each chamber for 72 nights. Nightly mosquito collections were made using light traps placed indoors. Temperature and carbon dioxide concentrations were measured using data loggers. Treatments and sleepers were rotated between huts using a randomized block design.

Results

When indoor light was visible outside the huts, there was an 84% increase in the odds of collecting mosquitoes indoors (Odds ratio, OR = 1.84, 95% confidence intervals, 95% CI 1.74–1.95, p < 0.001) compared with when it was not. Although the odds of collecting mosquitoes in huts with closed eaves (OR = 0.54, 95% CI 0.41–0.72, p < 0.001) was less than those with open eaves, few mosquitoes entered either type of well-ventilated hut. The odds of collecting mosquitoes was 99% less in well-ventilated huts, compared with poorly-ventilated traditional huts (OR = 0.01, 95% CI 0.01–0.03, p < 0.001). In well-ventilated huts, indoor temperatures were 1.3 °C (95% CI 0.9–1.7, p < 0.001) cooler, with lower carbon dioxide (CO2) levels (mean difference = 97 ppm, 77.8–116.2, p < 0.001) than in poorly-ventilated huts.

Conclusion

Although light visible from outside a hut increased mosquito house entry, good natural ventilation reduces indoor carbon dioxide concentrations, a major mosquito attractant, thereby reducing mosquito-hut entry.

Effect of roof colour on indoor temperature and human comfort levels, with implications for malaria control: a pilot study using experimental houses in rural Gambia

Background

In rural sub-Saharan Africa, thatch roofs are being replaced by metal roofs. Metal roofing, however, increases indoor temperatures above human comfort levels, and thus makes it more likely that residents will not use an insecticide-treated bed net (ITN) at night. Whether the colour of a metal roof affects indoor temperature and human comfort was assessed.

Methods

Two identical, experimental houses were constructed with metal roofs in rural Gambia. Roof types were: (1) original bare-metal, (2) painted with red oxide primer or (3) white gloss, to reflect solar radiation. Pairwise comparisons were run in six, five-night blocks during the malaria season 2018. Indoor climate was measured in each house and multivariate analysis used to compare indoor temperatures during the day and night.

Results

From 21.00 to 23.59 h, when most residents decide whether to use an ITN or not, the indoor temperature of a house with a bare metal roof was 31.5 °C (95% CI  31.2–31.8 °C), a red roof, 30.3 °C (95% CI 30.0–30.6) and a white roof, 29.8 °C (95% CI 29.4–30.1). During the same period, red-roofed houses were 1.23 °C cooler (95% CI 1.22–1.23) and white roofs 1.74 °C cooler (95% CI 1.70–1.79) than bare-metal roofed houses (p  < 0.001). Similar results were found from 00.00 to 06.00 h. Maximum daily temperatures were 0.93 °C lower in a white-roofed house (95% CI  0.10–0.30, p  < 0.001), but not a red roof (mean maximum temperature difference  = 0.44 °C warmer, 95% CI  0.43–0.45, p  = 0.081), compared with the bare-metal roofed houses. Human comfort analysis showed that from 21.00 to 23.59 h houses with white roofs (comfortable for 87% time) were more comfortable than bare-metal roofed houses (comfortable for 13% time; odds ratio  = 43.7, 95% CI 27.5–69.5, p  < 0.001). The cost of painting a metal roof white is approximately 31–68 USD.

Conclusions

Houses with a white roof were consistently cooler and more comfortable than those with a bare metal roof. Painting the roofs of houses white is a cheap way of making a dwelling more comfortable for the occupants and could potentially increase bed net use in hot humid countries.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12936-021-03951-4.

Impact of increased ventilation on indoor temperature and malaria mosquito density: an experimental study in The Gambia

In sub-Saharan Africa, cooler houses would increase the coverage of insecticide-treated bednets, the primary malaria control tool. We examined whether improved ventilation, using windows screened with netting, cools houses at night and reduces malaria mosquito house entry in The Gambia. Identical houses were constructed, with badly fitting doors the only mosquito entry points. Two men slept in each house and mosquitoes captured using light traps. First, temperature and mosquito density were compared in four houses with 0, 1, 2 and 3 screened windows. Second, carbon dioxide (CO2), a major mosquito attractant, was measured in houses with (i) no windows, (ii) screened windows and (iii) screened windows and screened doors. Computational fluid dynamic modelling captured the spatial movement of CO2. Increasing ventilation made houses cooler, more comfortable and reduced malaria mosquito house entry; with three windows reducing mosquito densities by 95% (95%CI = 90-98%). Screened windows and doors reduced the indoor temperature by 0.6°C (95%CI = 0.5-0.7°C), indoor CO2 concentrations by 31% between 21.00 and 00.00 h and malaria mosquito entry by 76% (95%CI = 69-82%). Modelling shows screening reduces CO2 plumes from houses. Under our experimental conditions, cross-ventilation not only reduced indoor temperature, but reduced the density of house-entering malaria mosquitoes, by weakening CO2 plumes emanating from houses.

Improved housing versus usual practice for additional protection against clinical malaria in The Gambia (RooPfs): a household-randomised controlled trial

BACKGROUND

In malaria-endemic areas, residents of modern houses have less malaria than those living in traditional houses. We aimed to assess whether children in The Gambia received an incremental benefit from improved housing, where current best practice of insecticide-treated nets, indoor residual spraying, seasonal malaria chemoprevention in children younger than 5 years, and prompt treatment against clinical malaria was in place.

METHODS

In this randomised controlled study, 800 households with traditional thatched-roofed houses were randomly selected from 91 villages in the Upper River Region of The Gambia. Within each village, equal numbers of houses were randomly allocated to the control and intervention groups using a sampling frame. Houses in the intervention group were modified with metal roofs and screened doors and windows, whereas houses in the control group received no modifications. In each group, clinical malaria in children aged 6 months to 13 years was monitored by active case detection over 2 years (2016-17). We did monthly collections from indoor light traps to estimate vector densities. Primary endpoints were the incidence of clinical malaria in study children with more than 50% of observations each year and household vector density. The trial is registered at ISRCTN02622179.

FINDINGS

In June, 2016, 785 houses had one child each recruited into the study (398 in unmodified houses and 402 in modified houses). 26 children in unmodified houses and 28 children in modified houses did not have at least 50% of visits in a year and so were excluded from analysis. 38 children in unmodified houses were recruited after study commencement, as were 21 children in modified houses, meaning 410 children in unmodified houses and 395 in modified houses were included in the parasitological analyses. At the end of the study, 659 (94%) of 702 children were reported to have slept under an insecticide-treated net; 662 (88%) of 755 children lived in houses that received indoor residual spraying; and 151 (90%) of 168 children younger than 5 years had seasonal malaria chemoprevention. Incidence of clinical malaria was 0·12 episodes per child-year in children in the unmodified houses and 0·20 episodes per child-year in the modified houses (unadjusted incidence rate ratio [RR] 1·68 [95% CI 1·11-2·55], p=0·014). Household vector density was 3·30 Anopheles gambiae per house per night in the unmodified houses compared with 3·60 in modified houses (unadjusted RR 1·28 [0·87-1·89], p=0·21).

INTERPRETATION

Improved housing did not provide protection against clinical malaria in this area of low seasonal transmission with high coverage of insecticide-treated nets, indoor residual spraying, and seasonal malaria chemoprevention.

FUNDING

Global Health Trials funded by Medical Research Council, UK Department for International Development, and Wellcome Trust.

Crowding has consequences: Prevention and management of COVID-19 in informal urban settlements

COVID-19 spreads via aerosols, droplets, fomites and faeces. The built environment that facilitates crowding increases exposure and hence transmission of COVID-19 as evidenced by outbreaks in both cool-dry and hot-humid climates, such as in the US prison system and dormitories in Singapore, respectively. This paper explores how the built environment influences crowding and COVID-19 transmission, focusing on informal urban settlements (slums). We propose policy and practice changes that could reduce COVID-19 transmission. There are several issues on how COVID-19 affects informal urban settlements. Slum populations tend to be younger than the overall population. Lower numbers of older people lessen the morbidity and mortality of the pandemic in slum areas. Second, many slum populations are highly mobile. By returning to their ancestral villages residents can avoid the risks of overcrowding and reduce the population density in a given area but may spread COVID-19 to other areas. Third, detection and registration of COVID-19 cases depends on patients presenting to health care providers. If the risk of visiting a health care centre outweighs the potential benefits patients may prefer not to seek treatment. The control and prevention of COVID-19 in informal urban settlements starts with organizing community infrastructure for diagnosis and treatment and assuring that basic needs (food, water, sanitation, health care and public transport) are met during quarantine. Next, community members at highest risk need to be identified and protected. Low-income, informal settlements need to be recognized as a reservoir and source for persistent transmission. Solutions to overcrowding must be developed for this and future pandemics. In view of the constant risk that slums present to the entire population decisive steps need to be taken to rehabilitate and improve informal settlements, while avoiding stigmatization.

Recommendations for building out mosquito-transmitted diseases in sub-Saharan Africa: the DELIVER mnemonic

In sub-Saharan Africa, most transmission of mosquito-transmitted diseases, such as malaria or dengue, occurs within or around houses. Preventing mosquito house entry and reducing mosquito production around the home would help reduce the transmission of these diseases. Based on recent research, we make key recommendations for reducing the threat of mosquito-transmitted diseases through changes to the built environment. The mnemonic, DELIVER, recommends the following best practices: (i) Doors should be screened, self-closing and without surrounding gaps; (ii) Eaves, the space between the wall and roof, should be closed or screened; (iii) houses should be Lifted above the ground; (iv) Insecticide-treated nets should be used when sleeping in houses at night; (v) houses should be Ventilated, with at least two large-screened windows to facilitate airflow; (vi) Environmental management should be conducted regularly inside and around the home; and (vii) Roofs should be solid, rather than thatch. DELIVER is a package of interventions to be used in combination for maximum impact. Simple changes to the built environment will reduce exposure to mosquito-transmitted diseases and help keep regions free from these diseases after elimination. This article is part of the theme issue 'Novel control strategies for mosquito-borne diseases'.

Old age is associated with decreased wealth in rural villages in Mtwara, Tanzania: findings from a cross-sectional survey

Objective

In many countries, housing is used for wealth accumulation and provides financial security in old age. We tested the hypothesis that household wealth, measured by housing quality and ownership of durable assets, would increase with age of the household head.

Methods

We conducted a survey of household heads in 68 villages surrounding Mtwara town, Tanzania and recorded relevant demographic, housing and social characteristics for each household. The primary analysis assessed the relationship between age of the household head, quality of the house structure and socio‐economic score (SES) using multivariate analysis. Principal Components Analysis (PCA) was used as a data reduction tool to estimate the social‐economic status of subjects based on relevant variables that are considered as proxy for SES.

Results

Of 13 250 household heads were surveyed of whom 49% were male. Those at least 50 years old were more likely to live in homes with an earth floor (86%) compared to younger household heads (80%; P < 0.0001), wattle and daub walls (94% vs. 90%; P < 0.0001) and corrugated iron roofs (56% vs. 52%; P < 0.0001). Wealth accumulation in the villages included in the study tends to be an inverted V‐relationship with age. Housing quality and SES rose to a peak by 50 years and then rapidly decreased. Households with a large number of members were more likely to have better housing than smaller households.

Conclusions

Housing plays a critical role in wealth accumulation and socio‐economic status of a household in rural villages in Tanzania. Households with a head under 50 years were more likely to live in improved housing and enjoyed a higher SES, than households with older heads. Larger families may provide protection against old age poverty in rural areas. Assuring financial security in old age, specifically robust and appropriate housing would have wide‐ranging benefits.

Housing and child health in sub-Saharan Africa: A cross-sectional analysis

BACKGROUND

Housing is essential to human well-being but neglected in global health. Today, housing in Africa is rapidly improving alongside economic development, creating an urgent need to understand how these changes can benefit health. We hypothesised that improved housing is associated with better health in children living in sub-Saharan Africa (SSA). We conducted a cross-sectional analysis of housing conditions relative to a range of child health outcomes in SSA.

METHODS AND FINDINGS

Cross-sectional data were analysed for 824,694 children surveyed in 54 Demographic and Health Surveys, 21 Malaria Indicator Surveys, and two AIDS Indicator Surveys conducted in 33 countries between 2001 and 2017 that measured malaria infection by microscopy or rapid diagnostic test (RDT), diarrhoea, acute respiratory infections (ARIs), stunting, wasting, underweight, or anaemia in children aged 0-5 years. The mean age of children was 2.5 years, and 49.7% were female. Housing was categorised into a binary variable based on a United Nations definition comparing improved housing (with improved drinking water, improved sanitation, sufficient living area, and finished building materials) versus unimproved housing (all other houses). Associations between house type and child health outcomes were determined using conditional logistic regression within surveys, adjusting for prespecified covariables including age, sex, household wealth, insecticide-treated bed net use, and vaccination status. Individual survey odds ratios (ORs) were pooled using random-effects meta-analysis. Across surveys, improved housing was associated with 8%-18% lower odds of all outcomes except ARI (malaria infection by microscopy: adjusted OR [aOR] 0.88, 95% confidence intervals [CIs] 0.80-0.97, p = 0.01; malaria infection by RDT: aOR 0.82, 95% CI 0.77-0.88, p < 0.001; diarrhoea: aOR 0.92, 95% CI 0.88-0.97, p = 0.001; ARI: aOR 0.96, 95% CI 0.87-1.07, p = 0.49; stunting: aOR 0.83, 95% CI 0.77-0.88, p < 0.001; wasting: aOR 0.90, 95% CI 0.83-0.99, p = 0.03; underweight: aOR 0.85, 95% CI 0.80-0.90, p < 0.001; any anaemia: aOR 0.87, 95% CI 0.82-0.92, p < 0.001; severe anaemia: aOR 0.89, 95% CI 0.84-0.95, p < 0.001). In comparison, insecticide-treated net use was associated with 16%-17% lower odds of malaria infection (microscopy: aOR 0.83, 95% CI 0.78-0.88, p < 0.001; RDT: aOR 0.84, 95% CI 0.79-0.88, p < 0.001). Drinking water source and sanitation facility alone were not associated with diarrhoea. The main study limitations are the use of self-reported diarrhoea and ARI, as well as potential residual confounding by socioeconomic position, despite adjustments for household wealth and education.

CONCLUSIONS

In this study, we observed that poor housing, which includes inadequate drinking water and sanitation facility, is associated with health outcomes known to increase child mortality in SSA. Improvements to housing may be protective against a number of important childhood infectious diseases as well as poor growth outcomes, with major potential to improve children's health and survival across SSA.

Knowledge gaps in the construction of rural healthy homes: A research agenda for improved low-cost housing in hot-humid Africa

Lorenz von Seidlein and colleagues discuss improving house designs in rural Africa to benefit health.

New Prototype Screened Doors and Windows for Excluding Mosquitoes from Houses: A Pilot Study in Rural Gambia

Despite compelling evidence that modern housing protects against malaria, houses in endemic areas are still commonly porous to mosquitoes. The protective efficacy of four prototype screened doors and two windows designs against mosquito house entry, their impact on indoor climate, as well as their use, durability and acceptability was assessed in a Gambian village. A baseline survey collected data on all the houses and discrete household units, each consisting of a front and back room, were selected and randomly allocated to the study arms. Each prototype self-closing screened door and window was installed in six and 12 units, respectively, with six unaltered units serving as controls. All prototype doors reduced the number of house-entering mosquitoes by 59–77% in comparison with the control houses. The indoor climate of houses with screened doors was similar to control houses. Seventy-nine percentage of door openings at night occurred from dusk to midnight, when malaria vectors begin entering houses. Ten weeks after installation the doors and windows were in good condition, although 38% of doors did not fully self-close and latch (snap shut). The new doors and windows were popular with residents. The prototype door with perforated concertinaed screening was the best performing door because it reduced mosquito entry, remained fully functional, and was preferred by the villagers. Screened doors and windows may be useful tools for reducing vector exposure and keeping areas malaria-free after elimination, when investment in routine vector control becomes difficult to maintain.

Reduced mosquito survival in metal-roof houses may contribute to a decline in malaria transmission in sub-Saharan Africa

In The Gambia, metal-roof houses were hotter during the day than thatched-roof houses. After 24 h, the mortality of Anopheles gambiae, the principal African malaria vector, was 38% higher in metal-roof houses than thatched ones. During the day, mosquitoes in metal-roof houses moved from the hot roof to cooler places near the floor, where the temperature was still high, reaching 35 °C. In laboratory studies, at 35 °C few mosquitoes survived 10 days, the minimum period required for malaria parasite development. Analysis of epidemiological data showed there was less malaria and lower vector survival rates in Gambian villages with a higher proportion of metal roofs. Our findings are consistent with the hypothesis that the indoor climate of metal-roof houses, with higher temperatures and lower humidity, reduces survivorship of indoor-resting mosquitoes and may have contributed to the observed reduction in malaria burden in parts of sub-Saharan Africa.

Mapping changes in housing in sub-Saharan Africa from 2000 to 2015

Access to adequate housing is a fundamental human right, essential to human security, nutrition and health, and a core objective of the United Nations Sustainable Development Goals1,2. Globally, the housing need is most acute in Africa, where the population will more than double by 2050. However, existing data on housing quality across Africa are limited primarily to urban areas and are mostly recorded at the national level. Here we quantify changes in housing in sub-Saharan Africa from 2000 to 2015 by combining national survey data within a geostatistical framework. We show a marked transformation of housing in urban and rural sub-Saharan Africa between 2000 and 2015, with the prevalence of improved housing (with improved water and sanitation, sufficient living area and durable construction) doubling from 11% (95% confidence interval, 10-12%) to 23% (21-25%). However, 53 (50-57) million urban Africans (47% (44-50%) of the urban population analysed) were living in unimproved housing in 2015. We provide high-resolution, standardized estimates of housing conditions across sub-Saharan Africa. Our maps provide a baseline for measuring change and a mechanism to guide interventions during the era of the Sustainable Development Goals.

In situ NAP-XPS spectroscopy during methane dry reforming on ZrO2/Pt(1 1 1) inverse model catalyst

Due to the need of sustainable energy sources, methane dry reforming is a useful reaction for conversion of the greenhouse gases CH₄ and CO₂ to synthesis gas (CO  +  H₂). Syngas is the basis for a wide range of commodity chemicals and can be utilized for fuel production via Fischer-Tropsch synthesis. The current study focuses on spectroscopic investigations of the surface and reaction properties of a ZrO₂/Pt inverse model catalyst, i.e. ZrO₂ particles (islands) grown on a Pt(1 1 1) single crystal, with emphasis on in situ near ambient pressure x-ray photoelectron spectroscopy (NAP-XPS) during MDR reaction. In comparison to technological systems, model catalysts facilitate characterization of the surface (oxidation) state, surface adsorbates, and the role of the metal-support interface. Using XPS and infrared reflection absorption spectroscopy we demonstrated that under reducing conditions (UHV or CH₄) the ZrO₂ particles transformed to an ultrathin ZrO₂ film that started to cover (wet) the Pt surface in an SMSI-like fashion, paralleled by a decrease in surface/interface oxygen. In contrast, (more oxidizing) dry reforming conditions with a 1:1 ratio of CH₄ and CO₂ were stabilizing the ZrO₂ particles on the model catalyst surface (or were even reversing the strong metal support interaction (SMSI) effect), as revealed by in situ XPS. Carbon deposits resulting from CH₄ dissociation were easily removed by CO₂ or by switching to dry reforming conditions (673-873 K). Thus, at these temperatures the active Pt surface remained free of carbon deposits, also preserving the ZrO₂/Pt interface.

Ambient pressure phase transitions over Ir(1 1 1): at the onset of CO oxidation

In this study we report on the adsorbate structures on an Ir(1 1 1) surface during the phase transition from the inactive to the active state during CO oxidation. The CO oxidation over Pt(1 1 1) is used as a reference case. Where Pt(1 1 1) either is inactive and CO covered or active and O covered, Ir(1 1 1) exhibits a transition state with co-existing chemisorbed O and CO. The observed structural differences are explained in terms of DFT-calculated adsorption energies. For Pt(1 1 1) the repulsive CO-O interaction makes co-existing chemisorbed CO and O unfavourable, while for Ir(1 1 1) the stronger O and CO adsorption allows for overcoming the repulsive interaction. At the onset of CO oxidation over Ir(1 1 1), a CO structure containing defects forms, which enables O₂ to dissociatively adsorb on the Ir(1 1 1) surface, thus enabling the CO oxidation reaction. At the mass transfer limit, the Ir(1 1 1) surface is covered by a chemisorbed O structure with defects; hence, the active surface is predominately chemisorbed O covered at a total pressure of 0.5 mbar and no oxide formation is observed.

Sonogashira cross-coupling over Au(1 1 1): from UHV to ambient pressure

We have studied the reaction of phenylacetylene (PA) with chloro-, bromo-, and iodobenzene on the Au(1 1 1) surface as a model system for the gold-catalysed Sonogashira cross-coupling. Both ultrahigh vacuum-based and ambient pressure x-ray photoelectron spectroscopy show that iodo- and chlorobenzene (IB and CB) undergo the cross-coupling reaction towards diphenylacetylene. Bromobenzene (BB), in contrast, does not react in the UHV experiments. Further, at ambient pressure signs are found for poisoning of the Au(1 1 1) surface by a carbon species formed in the reaction. The understanding obtained in the reaction experiments are based on a thorough investigation of the adsorption of PA, IB, CB, and BB on the Au(1 1 1) surface by soft x-ray absorption spectroscopy and temperature-dependent x-ray photoelectron spectroscopy. In particular, the experiments provide the orientation of the intact adsorbates with respect to the surfaces at liquid nitrogen temperature. Dissociation in the temperature regime between  -80 and  -15 °C is observed for iodo- and chlorobenzene, but not for BB, in agreement with that only IB and CB, but not BB, react with PA to form diphenylacetylene. The difference is tentatively attributed to a difference in surface orientation of the different halobenzenes.

Preventing sintering of nanoclusters on graphene by radical adsorption

Metal nanoclusters, supported on inert substrates, exhibiting well-defined shapes and sizes in a broad range of temperatures are a major object of desire in nanotechnology. Here, a technique is presented that improves the thermal stability of monodisperse and crystalline transition metal nanoclusters grown in a regular array on metal-supported graphene. To stabilize the clusters after growth under ultrahigh vacuum the system composed of the aggregates and the graphene/metal interface is exposed to radicals resulting from the dissociation of diatomic gases. As a model system we have used Pt as the metal element for cluster growth and the template consisting of the moiré pattern resulting from the lattice mismatch between graphene and the Ir(111) surface. The study has been performed for deuterium and oxygen radicals, which interact very differently with graphene. Our results reveal that after radical exposure the thermally activated motion of Pt nanoclusters to adjacent moiré cells and the subsequent sintering of neighbor aggregates are avoided, most pronounced for the case of atomic O. For the case of D the limits of the improvement are given by radical desorption, whereas for the case of O they are defined by an interplay between coalescence and graphene etching followed by Pt intercalation, which can be controlled by the amount of exposure. Finally, we determined the mechanism of how radical adsorption improves the thermal stability of the aggregates.

The RooPfs study to assess whether improved housing provides additional protection against clinical malaria over current best practice in The Gambia: study protocol for a randomized controlled study and ancillary studies

BACKGROUND

In malaria-endemic areas, residents of modern houses have less malaria than those living in traditional houses. This study will determine if modern housing provides incremental protection against clinical malaria over the current best practice of long-lasting insecticidal nets (LLINs) and prompt treatment in The Gambia, determine the incremental cost-effectiveness of the interventions, and analyze the housing market in The Gambia.

METHODS/DESIGN

A two-armed, household, cluster-randomized, controlled study will be conducted to assess whether improved housing and LLINs combine to provide better protection against clinical malaria in children than LLINs alone in The Gambia. The unit of randomization will be the household, defined as a house and its occupants. A total of 800 households will be enrolled and will receive LLINs, and 400 will receive improved housing before clinical follow-up. One child aged 6 months to 13 years will be enrolled from each household and followed for clinical malaria using active case detection to estimate malaria incidence for two malaria transmission seasons. Episodes of clinical malaria will be the primary endpoint. Study children will be surveyed at the end of each transmission season to estimate the prevalence of Plasmodium falciparum infection, parasite density, and the prevalence of anemia. Exposure to malaria parasites will be assessed using light traps, followed by detection of Anopheles gambiae species and sporozoite infection. Ancillary economic and social science studies will undertake a cost-effectiveness analysis and use qualitative and participatory methods to explore the acceptability of the housing modifications and to design strategies for scaling-up housing interventions.

DISCUSSION

The study is the first of its kind to measure the efficacy of housing on reducing clinical malaria, assess the incremental cost-effectiveness of improved housing, and identify mechanisms for scaling up housing interventions. Trial findings will help inform policy makers on improved housing for malaria control in sub-Saharan Africa.

TRIAL REGISTRATION

ISRCTN Registry, ISRCTN02622179 . Registered on 23 September 2014.

Malaria Epidemiology in Kilifi, Kenya during the 21st Century: What Next?

Lorenz von Seidlein and Jakob Knudsen discuss the changes in malaria incidence recorded at a single site in Africa over 25 years, along with future implications for disease prevention.

A novel deletion partly removing the AVP gene causes autosomal recessive inheritance of early-onset neurohypophyseal diabetes insipidus

Familial neurohypophyseal diabetes insipidus (FNDI) typically presents with age-dependent penetrance and autosomal dominant inheritance caused by missense variations in one allele of the AVP gene encoding the arginine vasopressin (AVP) prohormone. We present the molecular genetic characteristics underlying an unusual form of FNDI occurring with very early onset and seemingly autosomal recessive inheritance. By DNA amplification and sequencing, we identified a novel variant allele of the AVP gene carrying a 10,396 base pair deletion involving the majority of the AVP gene as well as its regulatory sequences in the intergenic region between the AVP and the OXT gene, encoding the oxytocin prohormone. We found two chromosomes carrying the deletion in affected family members and one in unaffected family members suspected to transmit the deleted allele. Whole-genome array analysis confirmed the results and excluded the presence of any additional major pathogenic abnormalities. The deletion is predicted to abolish the transcription of the AVP gene, thus the fact that family members heterozygous for the deletion remain healthy argues, in general, against haploinsufficiency as the pathogenic mechanism FNDI. Accordingly, our data is strong support to the prevailing idea that dominant inheritance of FNDI is due to a dominant-negative effect exerted by variant AVP prohormone.

Tuning the spin state of iron phthalocyanine by ligand adsorption

The future use of single-molecule magnets in applications will require the ability to control and manipulate the spin state and magnetization of the magnets by external means. There are different approaches to this control, one being the modification of the magnets by adsorption of small ligand molecules. In this paper we use iron phthalocyanine supported by an Au(111) surface as a model compound and demonstrate, using x-ray photoelectron spectroscopy and density functional theory, that the spin state of the molecule can be tuned to different values (S ∼ 0, [Formula: see text], 1) by adsorption of ammonia, pyridine, carbon monoxide or nitric oxide on the iron ion. The interaction also leads to electronic decoupling of the iron phthalocyanine from the Au(111) support.

Extended one-dimensional supramolecular assembly on a stepped surface

2,6-naphthalene-dicarboxylic acid was adsorbed on a Ag110 surface with an average terrace width of only some tens of a nm. Scanning tunneling microscopy shows that the adsorbates self-assemble into one-dimensional mesoscale length chains. These extend over several hundred nanometers and thus the structure exhibits an unprecedented tolerance to monatomic surface steps. Density functional theory and x-ray photoelectron spectroscopy explain the behavior by a strong intermolecular hydrogen bond plus a distinct template-mediated directionality and a high degree of molecular backbone flexibility.

STAT5 activity in pancreatic beta-cells influences the severity of diabetes in animal models of type 1 and 2 diabetes

Pancreatic beta-cell growth and survival and insulin production are stimulated by growth hormone and prolactin through activation of the transcription factor signal transducer and activator of transcription (STAT)5. To assess the role of STAT5 activity in beta-cells in vivo, we generated transgenic mice that expressed a dominant-negative mutant of STAT5a (DNSTAT5) or constitutive active mutant of STAT5b (CASTAT5) under control of the rat insulin 1 promoter (RIP). When subjected to a high-fat diet, RIP-DNSTAT5 mice showed higher body weight, increased plasma glucose levels, and impairment of glucose tolerance, whereas RIP-CASTAT5 mice were more glucose tolerant and less hyperleptinemic than wild-type mice. Although the pancreatic insulin content and relative beta-cell area were increased in high-fat diet-fed RIP-DNSTAT5 mice compared with wild-type or RIP-CASTAT5 mice, RIP-DNSTAT5 mice showed reduced beta-cell proliferation at 6 months of age. The inhibitory effect of high-fat diet or leptin on insulin secretion was diminished in isolated islets from RIP-DNSTAT5 mice compared with wild-type islets. Upon multiple low-dose streptozotocin treatment, RIP-DNSTAT5 mice exhibited higher plasma glucose levels, lower plasma insulin levels, and lower pancreatic insulin content than wild-type mice, whereas RIP-CASTAT5 mice maintained higher levels of plasma insulin. In conclusion, our results indicate that STAT5 activity in beta-cells influences the susceptibility to experimentally induced type 1 and type 2 diabetes.

Revisiting the structure of the p(4 x 4) surface oxide on Ag(111)

Scanning tunneling microscopy (STM) and density-functional theory are used to reexamine the structure of the renowned p(4 x 4)-O/Ag(111) surface oxide. The accepted structural model [C. I. Carlisle, Phys. Rev. Lett. 84, 3899 (2000)10.1103/PhysRevLett.84.3899] is incompatible with the enhanced resolution of the current STM measurements. An "Ag6 model" is proposed that is more stable than its predecessor and accounts for the coexistence of the p(4 x 4) and a novel c(3 x 5log3)rect phase. This coexistence is an indication of the dynamic complexity of the system that until now has not been appreciated.

Breakdown of disordered media by surface loads

We model an interface layer connecting two parts of a solid body by N parallel elastic springs connecting two rigid blocks. We load the system by a shear force acting on the top side. The springs have equal stiffness but are ruptured randomly when the load reaches a critical value. For the considered system, we calculate the shear modulus G as a function of the order parameter phi describing the state of damage, and also the "spalled"; material (burst) size distribution. In particular, we evaluate the relation between the damage parameter and the applied force and explore the behavior in the vicinity of material breakdown. Using this simple model for material breakdown, we show that damage, caused by applied shear forces, is analogous to a first-order phase transition. The scaling behavior of G with phi is explored analytically and numerically, close to phi=0 and phi=1 and in the vicinity of phi(c), when the shear load is close to but below the threshold force that causes material breakdown. Our model calculation represents a first approximation of a system subject to wear induced loads.

Acyl-coenzyme A organizes laterally in membranes and is recognized specifically by acyl-coenzyme A binding protein

Long chain acyl-coenzyme A (acyl-CoA) is a biochemically important amphiphilic molecule that is known to partition strongly into membranes by insertion of the acyl chain. At present, microscopically resolved evidence is lacking on how acyl-CoA influences and organizes laterally in membranes. By atomic force microscopy (AFM) imaging of membranes exposed to acyl-CoA in microM concentrations, it is shown that aggregate formation takes place within the membrane upon long-time exposure. It is known that acyl-CoA is bound by acyl-CoA binding protein (ACBP) with high affinity and specificity and that ACBP may bind and desorb membrane-bound acyl-CoA via a partly unknown mechanism. Following incubation with acyl-CoA, it is shown that ACBP is able to reverse the formation of acyl-CoA aggregates and to associate peripherally with acyl-CoA on the membrane surface. Our microscopic results point to the role of ACBP as an intermembrane transporter of acyl-CoA and demonstrate the ability of AFM to reveal the remodelling of membranes by surfactants and proteins.

Imiquimod 5% cream in the treatment of anogenital warts in female patients

OBJECTIVE

To investigate the efficacy and safety of imiquimod 5% cream in the treatment of anogenital warts in a female population.

METHODS

In two open-label studies, female patients with anogenital warts applied imiquimod 5% cream three times a week for up to 16 weeks. Patients who cleared their warts were monitored for a 6-month follow-up period. Patients could be re-treated with imiquimod 5% cream for up to an additional 16 weeks if their warts recurred or new warts developed during the follow-up period. The treatment period could also be extended for up to an additional 16 weeks if patients only experienced partial clearance during the initial 16-week treatment period.

RESULTS

Of the female patients who applied imiquimod 5% cream, 75% (449/600) experienced complete clearance of their warts (treatment failure analysis). This includes 46 patients who experienced total clearance when they applied imiquimod for longer than 16 weeks as their warts had only partially cleared in the initial 16 weeks of therapy. During the 6 months of follow-up after the initial treatment period, 15% of patients had recurrent warts. Thirty-nine (75%) of those patients experienced total clearance again after they re-applied imiquimod for up to an additional 16 weeks. The most frequently observed local skin reaction was erythema.

CONCLUSION

In these studies, imiquimod 5% cream was an effective and well-tolerated treatment for anogenital warts in females and continued to be safe and effective in the small proportion of patients who needed to re-apply imiquimod after wart recurrence.

The Acyl-CoA synthetases encoded within FAA1 and FAA4 in Saccharomyces cerevisiae function as components of the fatty acid transport system linking import, activation, and intracellular Utilization

Exogenous long-chain fatty acids are activated to coenzyme A derivatives prior to metabolic utilization. In the yeast Saccharomyces cerevisiae, the activation of these compounds prior to metabolic utilization proceeds through the fatty acyl-CoA synthetases Faa1p and Faa4p. Faa1p or Faa4p are essential for long-chain fatty acid import, suggesting that one or both of these enzymes are components of the fatty acid transport system, which also includes Fat1p. By monitoring the intracellular accumulation of the fluorescent long-chain fatty acid analogue 4,4-difluoro-5-methyl-4-bora-3a,4a-diaza-s-indacene-3-dodecanoic acid, long-chain fatty acid transport was shown to be severely restricted in a faa1 Delta faa4 Delta strain. These data established for the first time a mechanistic linkage between the import and activation of exogenous fatty acids in yeast. To investigate this linkage further, oleoyl CoA levels were defined following incubation of wild type and mutant cells with limiting concentrations of exogenous oleate. These studies demonstrated oleoyl CoA levels were reduced to less than 10% wild-type levels in faa1 Delta and faa1 Delta faa4 Delta strains. Defects in metabolic utilization and intracellular trafficking were also found in the fatty acyl-CoA synthetase-deficient strains. The faa1 Delta faa4 Delta strain had a marked reduction in endogenous acyl-CoA pools, suggesting these enzymes play a role in maintenance of endogenous acyl-CoA pools, metabolism and trafficking. In addition, this strain had levels of in vivo beta-oxidation of exogenous oleate reduced 3-fold when compared with the isogenic parent. Northern analyses demonstrated an additional defect in fatty acid trafficking as FAA1 or FAA4 were required for the transcriptional regulation of the genes encoding the peroxisomal enzymes acyl-CoA oxidase (POX1) and medium-chain acyl-CoA synthetase (FAA2). These data support the hypothesis that fatty acyl-CoA synthetase (Faa1p or Faa4p) functions as a component of the fatty acid import system by linking import and activation of exogenous fatty acids to intracellular utilization and signaling.

The interaction of acyl-CoA with acyl-CoA binding protein and carnitine palmitoyltransferase I

The affinity of recombinant rat acyl-CoA binding protein (ACBP) towards acyl-CoAs was investigated using both fluorimetric analysis and isothermal titration microcalorimetry, neither of which requires the physical separation of bound and free ligand for determining the dissociation constants (K(d)). The displacement of 11-(dansylamino)undecanoyl-CoA (DAUDA-CoA) from ACBP yielded binding parameters for the competing acyl-CoAs that compared favourably with those obtained using ultra-sensitive microcalorimetric titration. The K(d) values of ACBP for oleoyl-CoA and docosahexaenoyl-CoA are 0.014 and 0.016 microM, respectively. Under identical experimental conditions, carnitine palmitoyltransferase I (CPT I) of purified rat liver mitochondria has K(d) values of 2.4 and 22.7 microM for oleoyl-CoA and docosahexaenoyl-CoA, respectively. Given that CPT I was not only present at a much lower concentration but also has an appreciably lower affinity for acyl-CoAs than ACBP, it is proposed that CPT I is capable of interacting directly with ACBP-acyl-CoA binary complexes. This is supported by the fact that the enzyme activity correlated with the concentration of ACBP-bound acyl-CoA but not the free acyl-CoA. A transfer of acyl-CoA from ACBP-acyl-CoA binary complexes to CPT I could be a result of the enzyme inducing a conformational alteration in the ACBP leading to the release of acyl-CoA.

Acyl-CoA esters antagonize the effects of ligands on peroxisome proliferator-activated receptor alpha conformation, DNA binding, and interaction with Co-factors

The peroxisome proliferator-activated receptor alpha (PPARalpha) is a ligand-activated transcription factor and a key regulator of lipid homeostasis. Numerous fatty acids and eicosanoids serve as ligands and activators for PPARalpha. Here we demonstrate that S-hexadecyl-CoA, a nonhydrolyzable palmitoyl-CoA analog, antagonizes the effects of agonists on PPARalpha conformation and function in vitro. In electrophoretic mobility shift assays, S-hexadecyl-CoA prevented agonist-induced binding of the PPARalpha-retinoid X receptor alpha heterodimer to the acyl-CoA oxidase peroxisome proliferator response element. PPARalpha bound specifically to immobilized palmitoyl-CoA and Wy14643, but not BRL49653, abolished binding. S-Hexadecyl-CoA increased in a dose-dependent and reversible manner the sensitivity of PPARalpha to chymotrypsin digestion, and the S-hexadecyl-CoA-induced sensitivity required a functional PPARalpha ligand-binding pocket. S-Hexadecyl-CoA prevented ligand-induced interaction between the co-activator SRC-1 and PPARalpha but increased recruitment of the nuclear receptor co-repressor NCoR. In cells, the concentration of free acyl-CoA esters is kept in the low nanomolar range due to the buffering effect of high affinity acyl-CoA-binding proteins, especially the acyl-CoA-binding protein. By using PPARalpha expressed in Sf21 cells for electrophoretic mobility shift assays, we demonstrate that S-hexadecyl-CoA was able to increase the mobility of the PPARalpha-containing heterodimer even in the presence of a molar excess of acyl-CoA-binding protein, mimicking the conditions found in vivo.

Binding site differences revealed by crystal structures of Plasmodium falciparum and bovine acyl-CoA binding protein

Acyl-CoA binding protein (ACBP) maintains a pool of fatty acyl-CoA molecules in the cell and plays a role in fatty acid metabolism. The biochemical properties of Plasmodium falciparum ACBP are described together with the 2.0 A resolution crystal structures of a P. falciparum ACBP-acyl-CoA complex and of bovine ACBP in two crystal forms. Overall, the bovine ACBP crystal structures are similar to the NMR structures published previously; however, the bovine and parasite ACBP structures are less similar. The parasite ACBP is shown to have a different ligand-binding pocket, leading to an acyl-CoA binding specificity different from that of bovine ACBP. Several non-conservative differences in residues that interact with the ligand were identified between the mammalian and parasite ACBPs. These, together with measured binding-specificity differences, suggest that there is a potential for the design of molecules that might selectively block the acyl-CoA binding site.

Depletion of acyl-coenzyme A-binding protein affects sphingolipid synthesis and causes vesicle accumulation and membrane defects in Saccharomyces cerevisiae

Deletion of the yeast gene ACB1 encoding Acb1p, the yeast homologue of the acyl-CoA-binding protein (ACBP), resulted in a slower growing phenotype that adapted into a faster growing phenotype with a frequency >1:10(5). A conditional knockout strain (Y700pGAL1-ACB1) with the ACB1 gene under control of the GAL1 promoter exhibited an altered acyl-CoA profile with a threefold increase in the relative content of C18:0-CoA, without affecting total acyl-CoA level as previously reported for an adapted acb1Delta strain. Depletion of Acb1p did not affect the general phospholipid pattern, the rate of phospholipid synthesis, or the turnover of individual phospholipid classes, indicating that Acb1p is not required for general glycerolipid synthesis. In contrast, cells depleted for Acb1p showed a dramatically reduced content of C26:0 in total fatty acids and the sphingolipid synthesis was reduced by 50-70%. The reduced incorporation of [(3)H]myo-inositol into sphingolipids was due to a reduced incorporation into inositol-phosphoceramide and mannose-inositol-phosphoceramide only, a pattern that is characteristic for cells with aberrant endoplasmic reticulum to Golgi transport. The plasma membrane of the Acb1p-depleted strain contained increased levels of inositol-phosphoceramide and mannose-inositol-phosphoceramide and lysophospholipids. Acb1p-depleted cells accumulated 50- to 60-nm vesicles and autophagocytotic like bodies and showed strongly perturbed plasma membrane structures. The present results strongly suggest that Acb1p plays an important role in fatty acid elongation and membrane assembly and organization.

Acyl-CoA-binding protein in the armadillo Harderian gland: its primary structure and possible role in lipid secretion

Similar to those of other species, the Harderian glands of armadillo produce an abundant lipid secretion, most of which is composed of 1-alkyl-2,3-diacylglycerol. Biosynthesis of this component is apparently performed with the participation of one cytosolic pool of acyl-CoA and another of free fatty acids. The acyl-CoA-binding protein (ACBP) is present at a concentration at least 7-fold that of the heart-type fatty acid-binding protein (H-FABP), though lower than that in other armadillo organs such as liver and brain. The ACBP complete amino acid sequence was determined by Edman degradation of peptides generated by cleavage of the protein with cyanogen bromide, endopeptidase Glu-C, and trypsin. ACBP consists of 86 residues and has a calculated molecular mass of 9783 Da, taking into account that an acetyl group is blocking the N-terminus. Identity percentages between armadillo Harderian gland ACBP and other known ACBPs show that the protein belongs to the liver-specific ACBP isoform (L-ACBP). The fact that the ACBP concentration is higher than that of FABP suggests that the Harderian gland is able to store acyl-CoA amounts in ACBP larger than those of fatty acids in H-FABP for 1-alkyl-2,3-diacylglycerol synthesis.

Affinity labeling fatty acyl-CoA synthetase with 9-p-azidophenoxy nonanoic acid and the identification of the fatty acid-binding site

Fatty acyl-CoA synthetase (FACS, fatty acid:CoA ligase, AMP-forming, EC ) catalyzes the esterification of fatty acids to CoA thioesters for further metabolism and is hypothesized to play a pivotal role in the coupled transport and activation of exogenous long-chain fatty acids in Escherichia coli. Previous work on the bacterial enzyme identified a highly conserved region (FACS signature motif) common to long- and medium-chain acyl-CoA synthetases, which appears to contribute to the fatty acid binding pocket. In an effort to further define the fatty acid-binding domain within this enzyme, we employed the affinity labeled long-chain fatty acid [(3)H]9-p-azidophenoxy nonanoic acid (APNA) to specifically modify the E. coli FACS. [(3)H]APNA labeling of the purified enzyme was saturable and specific for long-chain fatty acids as shown by the inhibition of modification with increasing concentrations of palmitate. The site of APNA modification was identified by digestion of [(3)H]APNA cross-linked FACS with trypsin and separation and purification of the resultant peptides using reverse phase high performance liquid chromatography. One specific (3)H-labeled peptide, T33, was identified and following purification subjected to NH(2)-terminal sequence analysis. This approach yielded the peptide sequence PDATDEIIK, which corresponded to residues 422 to 430 of FACS. This peptide is immediately adjacent to the region of the enzyme that contains the FACS signature motif (residues 431-455). This work represents the first direct identification of the carboxyl-containing substrate-binding domain within the adenylate-forming family of enzymes. The structural model for the E. coli FACS predicts this motif lies within a cleft separating two distinct domains of the enzyme and is adjacent to a region that contains the AMP/ATP signature motif, which together are likely to represent the catalytic core of the enzyme.

Crystal structure of FadR, a fatty acid-responsive transcription factor with a novel acyl coenzyme A-binding fold

FadR is a dimeric acyl coenzyme A (acyl CoA)-binding protein and transcription factor that regulates the expression of genes encoding fatty acid biosynthetic and degrading enzymes in Escherichia coli. Here, the 2.0 A crystal structure of full-length FadR is described, determined using multi-wavelength anomalous dispersion. The structure reveals a dimer and a two-domain fold, with DNA-binding and acyl-CoA-binding sites located in an N-terminal and C-terminal domain, respectively. The N-terminal domain contains a winged helix-turn-helix prokaryotic DNA-binding fold. Comparison with known structures and analysis of mutagenesis data delineated the site of interaction with DNA. The C-terminal domain has a novel fold, consisting of a seven-helical bundle with a crossover topology. Careful analysis of the structure, together with mutational and biophysical data, revealed a putative hydrophobic acyl-CoA-binding site, buried in the core of the seven-helical bundle. This structure aids in understanding FadR function at a molecular level, provides the first structural scaffold for the large GntR family of transcription factors, which are keys in the control of metabolism in bacterial pathogens, and could thus be a possible target for novel chemotherapeutic agents.

Formation of hydrogen bonds precedes the rate-limiting formation of persistent structure in the folding of ACBP

A burst phase in the early folding of the four-helix two-state folder protein acyl-coenzyme A binding protein (ACBP) has been detected using quenched-flow in combination with site-specific NMR-detected hydrogen exchange. Several of the burst phase structures coincide with a structure consisting of eight conserved hydrophobic residues at the interface between the two N and C-terminal helices. Previous mutation studies have shown that the formation of this structure is rate limiting for the final folding of ACBP. The burst phase structures observed in ACBP are different from the previously reported collapsed types of burst phase intermediates observed in the folding of other proteins.

Structure and expression of the mouse gene encoding the endozepine-like peptide from haploid male germ cells

The endozepine-like peptide (ELP) represents a testis-specific isoform of the ubiquitous acyl-CoA binding protein (ACBP) and is highly expressed in late haploid stages of male germ cell development. The genomic sequence of the functional ELP gene as well as that of a pseudogene were analysed from independent bacteriophage clones of a 129sv mouse genomic library. Unlike the ACBP gene, which comprises four exons, the ELP gene has only a single intron within the region of the 5' untranslated region, suggesting that, like some other haploid expressed genes, the ELP gene might have evolved by retroposon-mediated gene duplication. Primer extension analysis was used to define the start site for transcription and hence the 5' promoter region. Electrophoretic mobility shift analysis was carried out on this region comparing nuclear extracts from adult mouse testis with those from mouse liver. Several testis-specific DNA-protein complexes were observed throughout 700 bp upstream of the transcription start site. One of these could be identified as corresponding to a steroidogenic factor-1 (SF-1) binding element. Further analysis using pure transcription factors showed that this element at position -340 was able to bind specifically to both SF-1 and to the germ cell nuclear factor (GCNF). Immunohistochemical analysis using an ELP-specific antibody showed that expression was very restricted within the testis to the postmeiotic germ cells, and in the ovary to interstitial/luteal cells, cell-types known to express GCNF and SF-1, respectively. Testes of CREM-tau knockout mice, lacking all spermatogenic stages later than round spermatids, were devoid of ELP immunoreactivity, whereas in RAD6 knockout mice the few remaining elongated spermatids were clearly defined by this excellent late haploid marker product. The ELP gene and its product thus offer an ideal system with which to investigate the differentiation of late haploid stages of spermatogenesis.

Murine FATP alleviates growth and biochemical deficiencies of yeast fat1Delta strains

Saccharomyces cerevisiae is an ideal model eukaryote for studying fatty-acid transport. Yeast are auxotrophic for unsaturated fatty acids when grown under hypoxic conditions or when the fatty-acid synthase inhibitor cerulenin is included in the growth media. The FAT1 gene encodes a protein, Fat1p, which is required for maximal levels of fatty-acid import and has an acyl CoA synthetase activity specific for very-long-chain fatty acids suggesting this protein plays a pivotal role in fatty-acid trafficking. In the present work, we present evidence that Fat1p and the murine fatty-acid transport protein (FATP) are functional homologues. FAT1 is essential for growth under hypoxic conditions and when cerulenin was included in the culture media in the presence or absence of unsaturated fatty acids. FAT1 disruptants (fat1Delta) fail to accumulate the fluorescent long-chain fatty acid fatty-acid analogue 4, 4-difluoro-5-methyl-4-bora-3a,4a-diaza-s-indacene-3-do decanoic acid (C1-BODIPY-C12), have a greatly diminished capacity to transport exogenous long-chain fatty acids, and have very long-chain acyl CoA synthetase activities that were 40% wild-type. The depression in very long-chain acyl CoA synthetase activities were not apparent in cells grown in the presence of oleate. Additionally, beta-oxidation of exogenous long-chain fatty acids is depressed to 30% wild-type levels. The reduction of beta-oxidation was correlated with a depression of intracellular oleoyl CoA levels in the fat1Delta strain following incubation of the cells with exogenous oleate. Expression of either Fat1p or murine FATP from a plasmid in a fat1Delta strain restored these phenotypic and biochemical deficiencies. Fat1p and FATP restored growth of fat1Delta cells in the presence of cerulenin and under hypoxic conditions. Furthermore, fatty-acid transport was restored and was found to be chain length specific: octanoate, a medium-chain fatty acid was transported in a Fat1p- and FATP-independent manner while the long-chain fatty acids myristate, palmitate, and oleate required either Fat1p or FATP for maximal levels of transport. Lignoceryl CoA synthetase activities were restored to wild-type levels in fat1Delta strains expressing either Fat1p or FATP. Fat1p or FATP also restored wild-type levels of beta-oxidation of exogenous long-chain fatty acids. These data show that Fat1p and FATP are functionally equivalent when expressed in yeast and play a central role in fatty-acid trafficking.

Crystallization and X-ray diffraction studies of the fatty-acid responsive transcription factor FadR from Escherichia coli

FadR, an acylCoA-dependent Escherichia coli transcription factor controlling the expression of genes involved in fatty-acid degradation and synthesis, has been crystallized. Crystals of two binary complexes were obtained. The FadR-CoA complex crystallized in space group C222(1), with unit-cell parameters a = 61.3, b = 102.0, c = 91.3 A. The FadR-octanoyl-CoA complex crystallized in space group P6(5)22, with unit-cell parameters a = b = 59.7, c = 296.2 A. Both crystal forms diffracted to 3.5 A on a rotating-anode generator. In both crystal forms, the asymmetric unit contains one subunit. The protein is known to be a homodimer; each subunit consists of two domains of unknown fold. For the acyl-CoA-binding domain, a previously undetected sequence homology to PAS domains, in particular the photoactive yellow protein, is reported.