TRAPs: the 'elevator-with-an-operator' mechanism.

Tripartite ATP-independent periplasmic (TRAP) transporters are nutrient-uptake systems found in bacteria and archaea. These evolutionary divergent transporter systems couple a substrate-binding protein (SBP) to an elevator-type secondary transporter, which is a first-of-its-kind mechanism of transport. Here, we highlight breakthrough TRAP transporter structures and recent functional data that probe the mechanism of transport. Furthermore, we discuss recent structural and biophysical studies of the ion transporter superfamily (ITS) members and highlight mechanistic principles that are relevant for further exploration of the TRAP transporter system.

Structures and General Transport Mechanisms by the Major Facilitator Superfamily (MFS).

The major facilitator superfamily (MFS) is the largest known superfamily of secondary active transporters. MFS transporters are responsible for transporting a broad spectrum of substrates, either down their concentration gradient or uphill using the energy stored in the electrochemical gradients. Over the last 10 years, more than a hundred different MFS transporter structures covering close to 40 members have provided an atomic framework for piecing together the molecular basis of their transport cycles. Here, we summarize the remarkable promiscuity of MFS members in terms of substrate recognition and proton coupling as well as the intricate gating mechanisms undergone in achieving substrate translocation. We outline studies that show how residues far from the substrate binding site can be just as important for fine-tuning substrate recognition and specificity as those residues directly coordinating the substrate, and how a number of MFS transporters have evolved to form unique complexes with chaperone and signaling functions. Through a deeper mechanistic description of glucose (GLUT) transporters and multidrug resistance (MDR) antiporters, we outline novel refinements to the rocker-switch alternating-access model, such as a latch mechanism for proton-coupled monosaccharide transport. We emphasize that a full understanding of transport requires an elucidation of MFS transporter dynamics, energy landscapes, and the determination of how rate transitions are modulated by lipids.

N-acetylmannosamine-6-phosphate 2-epimerase uses a novel substrate-assisted mechanism to catalyze amino sugar epimerization.

There are five known general catalytic mechanisms used by enzymes to catalyze carbohydrate epimerization. The amino sugar epimerase N-acetylmannosamine-6-phosphate 2-epimerase (NanE) has been proposed to use a deprotonation-reprotonation mechanism, with an essential catalytic lysine required for both steps. However, the structural determinants of this mechanism are not clearly established. We characterized NanE from Staphylococcus aureus using a new coupled assay to monitor NanE catalysis in real time and found that it has kinetic constants comparable with other species. The crystal structure of NanE from Staphylococcus aureus, which comprises a triosephosphate isomerase barrel fold with an unusual dimeric architecture, was solved with both natural and modified substrates. Using these substrate-bound structures, we identified the following active-site residues lining the cleft at the C-terminal end of the ß-strands: Gln11, Arg40, Lys63, Asp124, Glu180, and Arg208, which were individually substituted and assessed in relation to the mechanism. From this, we re-evaluated the central role of Glu180 in this mechanism alongside the catalytic lysine. We observed that the substrate is bound in a conformation that ideally positions the C5 hydroxyl group to be activated by Glu180 and donate a proton to the C2 carbon. Taken together, we propose that NanE uses a novel substrate-assisted proton displacement mechanism to invert the C2 stereocenter of N-acetylmannosamine-6-phosphate. Our data and mechanistic interpretation may be useful in the development of inhibitors of this enzyme or in enzyme engineering to produce biocatalysts capable of changing the stereochemistry of molecules that are not amenable to synthetic methods.

Optometry independent prescribing during COVID lockdown in Wales.

INTRODUCTION: During the COVID-19 lockdown, primary care optometry services in Wales moved to a hub model of provision. Three independent prescribing models were available in different areas: a commissioned Independent Prescribing Optometry Service (IPOS), independent prescribers that were not commissioned and no independent prescribers available. This allowed a unique opportunity for comparison. METHOD: Optometry practices completed an online survey for each patient episode. Analysis of the data gave insight into patient presentation to urgent eye services and the drugs prescribed by optometrists. Medicines prescribed, sold or given and onward referral were compared between areas with an IPOS service (n = 2), those with prescribers but no commissioned service (n = 2) and those with no prescribers (n = 2). RESULTS: Data from 22,434 reported patient episodes from 81 optometry practices in six health boards between 14 April 2020 and 30 June 2020 were analysed. Urgent care accounted for 10,997 (49.02%) first appointments and 1777 (7.92%) follow-ups. Most (18,006, 80.26%) patients self-referred. The most common presenting symptom was 'Eye pain/discomfort' (4818, 43.81% of urgent attendances). Anterior segment pathology was the most reported finding at first (6078, 55.27%) and follow-up (1316, 74.06%) urgent care appointments. Topical steroids (373, 25.99% of prescriptions) were the most prescribed medications. More medications were prescribed in areas with an IPOS service (1136, 79.16% of prescriptions) than areas with prescribers but no commissioned service. There were more follow-up appointments in optometric practice and fewer urgent referrals to ophthalmology in IPOS areas. CONCLUSION: Urgent care services were most utilised by patients with discomfort caused by anterior eye conditions. IPOS services enabled optometrists to manage conditions to resolution without referral and without reduction in medications sold or given. Commissioners should recognise the value in reducing burden in urgent ophthalmology and the need for follow-up as part of a commissioned independent prescribing service.

An analysis of glaucoma repeat measures assessment results: Are core competencies enough?

PURPOSE: The need to validate core competency skills in qualified optometrists wishing to take part in extended roles in glaucoma care has been questioned. This analysis examines the ability of qualified optometrists to perform relevant core competency skills under standardised objective assessment conditions to explore whether such validation is justified. It also investigates if there are associations between performance, gender and length of time since qualification. METHODS: Anonymised data from the Cardiff University assessment programme for the Wales Optometry Postgraduate Education Centre (WOPEC) Local Optical Committee Support Unit glaucoma referral filtering and monitoring pathway delivered between January 2017 and March 2020 were analysed. Results were combined with demographic data from the General Optical Council register of optometrists in the UK to investigate associations between performance and practitioner characteristics, namely length of time since qualification and gender. RESULTS: The assessment results of 2215 optometrists practising in England (approximately 15% of all UK registered optometrists and 30% of all optometrists registered in England) were analysed. Failure rates for first time assessment in each of five objective structured clinical examination style practical assessments were 8.5% (van Herick); 8.8% (slit lamp binocular indirect ophthalmoscopy); 10.1% (Goldmann applanation tonometry calibration); 21.9% (Goldmann applanation tonometry) and 23.3% (case scenario interpretation and management). There were either no associations or at most very weak associations between performance and practitioner characteristics. CONCLUSIONS: Our results suggest that these competencies are not universally present in optometrists practising in England and that ongoing training and assessment of these competencies is justified for entry into extended roles. There are no meaningful associations between performance in these assessments and gender or time since qualification.

A mixed-methods characterisation of patient safety incidents by primary eye care practitioners.

PURPOSE: Patient safety in eye health care is an underdeveloped field of research. A patient safety incident occurs when an unintended incident happens that could have (or did) lead to harm. To enable learning from patient safety incidents in optometry, a characterisation of commonly experienced safety incidents is needed to identify options to improve the quality of care. This study aimed to characterise eye health-related patient safety incidents from the perspective of eye care practitioners. METHODS: At a national conference in Wales, 56 eye care practitioners participated in a stakeholder workshop on eye care-related patient safety incidents. Participants were asked to suggest patient safety incidents that have occurred, or based on their experience, could occur in optometric practice. Using the nominal group technique, participants voted on the incident they perceived could cause the most harm and the incident observed most frequently in practice. Framework analysis supported identification of themes about the nature and outcomes of incidents in eye care. RESULTS: Diagnostic incidents were perceived to be the most severe (highest number of 'severity votes', n = 38), whilst administration-related incidents were most frequent (highest number of 'frequency votes' n = 39). Four themes were identified which are as follows: inappropriate clinical decision-making; delayed or missed referral of patients to general medical practitioners or ophthalmologists; compromised communication with other practitioners or patients and delays in receiving eye care. The results suggest that incidents relating to inappropriate clinical decision-making could result in the most severe harm to patients but may not occur frequently. CONCLUSIONS: Diagnostic- and administrative-related incidents pose clear challenges for improvement in quality and safety of care. The breadth of themes reflecting the nature and outcomes from unsafe eye care highlights the complexity underpinning incidents and the burden to patients. This work has informed the content of an all-Wales incident report form for primary eye care practitioners.

The basis for non-canonical ROK family function in the N-acetylmannosamine kinase from the pathogen Staphylococcus aureus.

In environments where glucose is limited, some pathogenic bacteria metabolize host-derived sialic acid as a nutrient source. N-Acetylmannosamine kinase (NanK) is the second enzyme of the bacterial sialic acid import and degradation pathway and adds phosphate to N-acetylmannosamine using ATP to prime the molecule for future pathway reactions. Sequence alignments reveal that Gram-positive NanK enzymes belong to the Repressor, ORF, Kinase (ROK) family, but many lack the canonical Zn-binding motif expected for this function, and the sugar-binding EXGH motif is altered to EXGY. As a result, it is unclear how they perform this important reaction. Here, we study the Staphylococcus aureus NanK (SaNanK), which is the first characterization of a Gram-positive NanK. We report the kinetic activity of SaNanK along with the ligand-free, N-acetylmannosamine-bound and substrate analog GlcNAc-bound crystal structures (2.33, 2.20, and 2.20 Å resolution, respectively). These demonstrate, in combination with small-angle X-ray scattering, that SaNanK is a dimer that adopts a closed conformation upon substrate binding. Analysis of the EXGY motif reveals that the tyrosine binds to the N-acetyl group to select for the "boat" conformation of N-acetylmannosamine. Moreover, SaNanK has a stacked arginine pair coordinated by negative residues critical for thermal stability and catalysis. These combined elements serve to constrain the active site and orient the substrate in lieu of Zn binding, representing a significant departure from canonical NanK binding. This characterization provides insight into differences in the ROK family and highlights a novel area for antimicrobial discovery to fight Gram-positive and S. aureus infections.

Structure-function analyses of two plant meso-diaminopimelate decarboxylase isoforms reveal that active-site gating provides stereochemical control.

meso-Diaminopimelate decarboxylase catalyzes the decarboxylation of meso-diaminopimelate, the final reaction in the diaminopimelate l-lysine biosynthetic pathway. It is the only known pyridoxal-5-phosphate-dependent decarboxylase that catalyzes the removal of a carboxyl group from a d-stereocenter. Currently, only prokaryotic orthologs have been kinetically and structurally characterized. Here, using complementation and kinetic analyses of enzymes recombinantly expressed in Escherichia coli, we have functionally tested two putative eukaryotic meso-diaminopimelate decarboxylase isoforms from the plant species Arabidopsis thaliana We confirm they are both functional meso-diaminopimelate decarboxylases, although with lower activities than those previously reported for bacterial orthologs. We also report in-depth X-ray crystallographic structural analyses of each isoform at 1.9 and 2.4 Å resolution. We have captured the enzyme structure of one isoform in an asymmetric configuration, with one ligand-bound monomer and the other in an apo-form. Analytical ultracentrifugation and small-angle X-ray scattering solution studies reveal that A. thaliana meso-diaminopimelate decarboxylase adopts a homodimeric assembly. On the basis of our structural analyses, we suggest a mechanism whereby molecular interactions within the active site transduce conformational changes to the active-site loop. These conformational differences are likely to influence catalytic activity in a way that could allow for d-stereocenter selectivity of the substrate meso-diaminopimelate to facilitate the synthesis of l-lysine. In summary, the A. thaliana gene loci At3g14390 and At5g11880 encode functional. meso-diaminopimelate decarboxylase enzymes whose structures provide clues to the stereochemical control of the decarboxylation reaction catalyzed by these eukaryotic proteins.

Impact of Eye Cosmetics on the Eye, Adnexa, and Ocular Surface.

Despite the fact that cosmetic products undergo rigorous testing to ensure they are safe for human use, some users report mild discomfort following their application. The cutaneous changes, such as allergic dermatitis, are well reported, but the ocular changes associated with eye cosmetic use are less so. Some pigmented cosmetic products may accumulate within the lacrimal system and conjunctivae over many years of use, but immediate reports of eye discomfort after application are most common. Changes to the tear film and its stability may occur shortly after application, and contact lens wearers can also be affected by lens spoliation from cosmetic products. Additionally, creams used in the prevention of skin aging are often applied around the eyes, and retinoids present in these formulations can have negative effects on meibomian gland function and may be a contributing factor to dry eye disease. The aim of this review is to summarize current knowledge regarding the impact of cosmetic products on the eye, ocular surface, and tear film.

Migration of Cosmetic Products into the Tear Film.

PURPOSE: To examine, record, and quantify the migration of a conventional eye cosmetic pencil when applied to periocular skin in two different locations: behind the lash line (ELI) and along the periocular skin (ELO). METHODS: This was a pilot study (prospective, randomized crossover design) involving two visits on separate days. Three female subjects were randomly assigned one of two eyeliner application conditions: ELI (inside the lash line) or ELO (anterior to the lash line). Pencil eyeliner ("Glimmerstick" in Graphite; Avon, Northampton, United Kingdom) was applied to the subject's upper and lower right eyelid by the examiner. Slitlamp video recording of glitter particles suspended within the tear film was conducted for 30 sec on 10 occasions up to 2 hr post-eyeliner application. The number of glitter particles suspended in the tear film, analyzed using ImageJ software, is reported. RESULTS: The migration of the glitter particles occurred more readily in ELI application, with maximum contamination of the tear film achieved 5 to 10 min post-application. The migration of eyeliner following ELO application was comparatively slower and reduced compared with ELI application. The quantity of glitter particles suspended in the tear film varied between subjects; however, 2 hr post-application, contamination of the tear film from pencil eyeliner was negligible. CONCLUSIONS: Pencil eyeliner migrates most readily and maximally contaminates the tear film when applied posterior to the lash line. This has implications for contact lens wearers and patients with dry eye syndrome or sensitive eyes. Eye cosmetic usage for participants involved in anterior eye and contact lens research should be carefully considered in the design of studies.

Branch retinal vein occlusion in an asymptomatic adult with cystic fibrosis.

PURPOSE: This article aims to describe a case of asymptomatic branch retinal vein occlusion (BRVO) in a patient with cystic fibrosis (CF) and discuss the possible link between the two. CASE REPORT: A young adult (aged 35 years) with CF who presented for routine ocular examination was found to have a superior temporal BRVO in the left eye. Visual acuity was unaffected, measuring -0.06 LogMAR, and intraocular pressure was 10 mm Hg. Optical coherence tomography showed no macular involvement. Regarding the patient's general health, blood pressure was within the normal range, and there was no diabetes. Exploratory blood tests revealed elevated fibrinogen levels. CONCLUSIONS: It is hypothesized that BRVO occurred secondary to raised fibrinogen levels, a common feature in CF resulting from chronic pulmonary infection and inflammation. Practitioners should be aware of the possible link between BRVO and CF.

The burden of acute eye conditions on different healthcare providers: a retrospective population-based study.

BACKGROUND: The demand for acute eyecare exponentially outstrips capacity. The public lacks awareness of community eyecare services. AIM: To quantify the burden of acute eyecare on different healthcare service providers in a national population through prescribing and medicines provision by GPs, optometrists, and pharmacists, and provision of care by accident and emergency (A&E) services. A secondary aim was to characterise some of the drivers of this burden. DESIGN AND SETTING: A retrospective data-linkage study set in Wales, UK. METHOD: Analysis of datasets was undertaken from the Secure Anonymised Information Linkage Databank (GP and A&E), the Eye Health Examination Wales service (optometry), and the Common Ailments Scheme (pharmacy) during 2017-2018. RESULTS: A total of 173 999 acute eyecare episodes delivered by GPs (168 877 episodes) and A&E services (5122) were identified during the study. This resulted in 65.4 episodes of care per 1000 people per year. GPs prescribed a total of 87 973 653 prescriptions within the general population. Of these, 820 693 were related to acute eyecare, resulting in a prescribing rate of 0.9%. A total of 5122 eye-related and 905 224 general A&E attendances were identified, respectively, resulting in an A&E attendance rate of 0.6%. Optometrists and pharmacists managed 51.8% (116 868) and 0.6% (2635) of all episodes, respectively. Older females and infants of both sexes were more likely to use GP prescribing services, while adolescent and middle-aged males were more likely to visit A&E. GP prescribing burden was driven partially by economic deprivation, access to services, and health score. Season, day of the week, and time of day were predictors of burden in GP and A&E. CONCLUSION: Acute eyecare continues to place considerable burden on GP and A&E services in Wales, particularly in urban areas with greater economic deprivation and lower overall health. This is likely to increase with a rapidly ageing population. With ongoing pathway development to better utilise optometry and pharmacy, and improved public awareness, there may be scope to change this trajectory.

Structural and biophysical analysis of a Haemophilus influenzae tripartite ATP-independent periplasmic (TRAP) transporter.

Tripartite ATP-independent periplasmic (TRAP) transporters are secondary-active transporters that receive their substrates via a soluble-binding protein to move bioorganic acids across bacterial or archaeal cell membranes. Recent cryo-electron microscopy (cryo-EM) structures of TRAP transporters provide a broad framework to understand how they work, but the mechanistic details of transport are not yet defined. Here we report the cryo-EM structure of the Haemophilus influenzae N-acetylneuraminate TRAP transporter (HiSiaQM) at 2.99 Å resolution (extending to 2.2 Å at the core), revealing new features. The improved resolution (the previous HiSiaQM structure is 4.7 Å resolution) permits accurate assignment of two Na+ sites and the architecture of the substrate-binding site, consistent with mutagenic and functional data. Moreover, rather than a monomer, the HiSiaQM structure is a homodimer. We observe lipids at the dimer interface, as well as a lipid trapped within the fusion that links the SiaQ and SiaM subunits. We show that the affinity (KD) for the complex between the soluble HiSiaP protein and HiSiaQM is in the micromolar range and that a related SiaP can bind HiSiaQM. This work provides key data that enhances our understanding of the 'elevator-with-an-operator' mechanism of TRAP transporters.

Cloning, expression, purification, crystallization and preliminary X-ray diffraction studies of N-acetylneuraminate lyase from methicillin-resistant Staphylococcus aureus.

The enzyme N-acetylneuraminate lyase (EC 4.1.3.3) is involved in the metabolism of sialic acids. Specifically, the enzyme catalyzes the retro-aldol cleavage of N-acetylneuraminic acid to form N-acetyl-D-mannosamine and pyruvate. Sialic acids comprise a large family of nine-carbon amino sugars, all of which are derived from the parent compound N-acetylneuraminic acid. In recent years, N-acetylneuraminate lyase has received considerable attention from both mechanistic and structural viewpoints and has been recognized as a potential antimicrobial drug target. The N-acetylneuraminate lyase gene was cloned from methicillin-resistant Staphylococcus aureus genomic DNA, and recombinant protein was expressed and purified from Escherichia coli BL21 (DE3). The enzyme crystallized in a number of crystal forms, predominantly from PEG precipitants, with the best crystal diffracting to beyond 1.70 Šresolution in space group P21. Molecular replacement indicates the presence of eight monomers per asymmetric unit. Understanding the structural biology of N-acetylneuraminate lyase in pathogenic bacteria, such as methicillin-resistant S. aureus, will provide insights for the development of future antimicrobials.

Structure and mechanism of a tripartite ATP-independent periplasmic TRAP transporter.

In bacteria and archaea, tripartite ATP-independent periplasmic (TRAP) transporters uptake essential nutrients. TRAP transporters receive their substrates via a secreted soluble substrate-binding protein. How a sodium ion-driven secondary active transporter is strictly coupled to a substrate-binding protein is poorly understood. Here we report the cryo-EM structure of the sialic acid TRAP transporter SiaQM from Photobacterium profundum at 2.97 Å resolution. SiaM comprises a "transport" domain and a "scaffold" domain, with the transport domain consisting of helical hairpins as seen in the sodium ion-coupled elevator transporter VcINDY. The SiaQ protein forms intimate contacts with SiaM to extend the size of the scaffold domain, suggesting that TRAP transporters may operate as monomers, rather than the typically observed oligomers for elevator-type transporters. We identify the Na+ and sialic acid binding sites in SiaM and demonstrate a strict dependence on the substrate-binding protein SiaP for uptake. We report the SiaP crystal structure that, together with docking studies, suggest the molecular basis for how sialic acid is delivered to the SiaQM transporter complex. We thus propose a model for substrate transport by TRAP proteins, which we describe herein as an 'elevator-with-an-operator' mechanism.

The accuracy of the inferior>superior>nasal>temporal neuroretinal rim area rule for diagnosing glaucomatous optic disc damage.

PURPOSE: To determine the accuracy with which the optic disc can be diagnosed as normal or glaucomatous according to the ISNT rule, whereby, in the normal eye, the neuroretinal rim area follows the order inferior (I) > superior (S) > nasal (N) > temporal (T). DESIGN: Prospective, cross-sectional, observational, case series. PARTICIPANTS: Fifty-one normal individuals and 78 individuals with open-angle glaucoma exhibiting field loss (median mean deviation, -4.37 dB; interquartile range [IQR], -2.10 to -7.96 dB; median pattern standard deviation, 5.65 dB; IQR, 2.94 to 8.56 dB). The reference diagnosis was made by 2 experts on the basis of the appearance of the optic disc and of the corresponding visual field. METHODS: Stereoscopic optic disc photographs, acquired for each individual, were digitized at high resolution and analyzed using a digital, quad-buffered, stereoscopic viewing system in which a Z screen was used to dissociate the images to the 2 eyes of the observer. Three expert observers, trained to fellowship standard in glaucoma, independently undertook planimetry of the neuroretinal rim and of the disc margin from 1 eye of each individual, using a cursor moving in stereoscopic space to minimize parallax errors. Software automatically calculated the neuroretinal rim area in 10°, 30°, 40°, and 90° segments. For the ISNT rule to be obeyed, the 3 Boolean comparisons of the neuroretinal rim area, I>S, S>N, and N>T, had to be true. If any of the comparisons returned false, the rule was considered not to have been obeyed. Values were compared at a precision of 0.0001 mm(2). MAIN OUTCOME MEASURES: The outcome of the ISNT rule in terms of the 3 Boolean comparisons of the neuroretinal rim area was specified in terms of the sensitivity, specificity, and hence, the positive and negative likelihood ratios. RESULTS: Based on the ISNT rule being obeyed for 10° segments, the positive likelihood ratio among the 3 observers was 1.11 (95% confidence interval [CI], 0.99-1.25), 1.07 (95% CI, 0.94-1.21), and 1.06 (95% CI, 0.96-1.18), respectively. It was similar for the other segment sizes. Variants of the rule were not appreciably better. CONCLUSIONS: The ISNT rule has limited utility in the diagnosis of open-angle glaucoma.

Eye cosmetic usage and associated ocular comfort.

PURPOSE: Eye cosmetics usage is commonplace and whilst some products such as eyeliner are applied with close proximity to the ocular surface, there is little knowledge of the short- and long-term ocular effects of eye cosmetic formulations. This study aimed to investigate the use of eye cosmetics and identify any relationships between ocular comfort and cosmetic usage. METHODS: Results were collated from an online survey comprising 23 questions that recorded demographics, Ocular Surface Disease Index (OSDI) score, extent and range of eye cosmetic use and perceived comfort differences with and without eye cosmetics. RESULTS: The 1360 female respondents (median age 25, interquartile range 20-34 years) completed the survey; 83% reported using eye cosmetics regularly (≥ 3 times per week) with mascara being most commonly used. Fifty three per cent used at least three different eye cosmetics products regularly. OSDI scores of cosmetics users were similar to non-users (p = 0.083), but perceived comfort was greater when cosmetics were not used (p < 0.001). In occasional cosmetics users (use of products < 3 times per week), 65% reported a reduction in comfort when cosmetics were used. Median OSDI scores suggested a trend towards reduced comfort amongst eyeliner users (p = 0.07) although frequency and type of cosmetic products used did not appear to influence OSDI scores. CONCLUSIONS: This study shows the use of multiple eye cosmetics is extensive and associated with the perception of ocular discomfort. With such widespread use of these products, more research is required to assess the effect on the ocular surface and tear film, which may be underestimated.

Mechanism of NanR gene repression and allosteric induction of bacterial sialic acid metabolism.

Bacteria respond to environmental changes by inducing transcription of some genes and repressing others. Sialic acids, which coat human cell surfaces, are a nutrient source for pathogenic and commensal bacteria. The Escherichia coli GntR-type transcriptional repressor, NanR, regulates sialic acid metabolism, but the mechanism is unclear. Here, we demonstrate that three NanR dimers bind a (GGTATA)3-repeat operator cooperatively and with high affinity. Single-particle cryo-electron microscopy structures reveal the DNA-binding domain is reorganized to engage DNA, while three dimers assemble in close proximity across the (GGTATA)3-repeat operator. Such an interaction allows cooperative protein-protein interactions between NanR dimers via their N-terminal extensions. The effector, N-acetylneuraminate, binds NanR and attenuates the NanR-DNA interaction. The crystal structure of NanR in complex with N-acetylneuraminate reveals a domain rearrangement upon N-acetylneuraminate binding to lock NanR in a conformation that weakens DNA binding. Our data provide a molecular basis for the regulation of bacterial sialic acid metabolism.

Selective Nutrient Transport in Bacteria: Multicomponent Transporter Systems Reign Supreme.

Multicomponent transporters are used by bacteria to transport a wide range of nutrients. These systems use a substrate-binding protein to bind the nutrient with high affinity and then deliver it to a membrane-bound transporter for uptake. Nutrient uptake pathways are linked to the colonisation potential and pathogenicity of bacteria in humans and may be candidates for antimicrobial targeting. Here we review current research into bacterial multicomponent transport systems, with an emphasis on the interaction at the membrane, as well as new perspectives on the role of lipids and higher oligomers in these complex systems.