Staphylococcal Periscope proteins Aap, SasG, and Pls project noncanonical legume-like lectin adhesin domains from the bacterial surface.

Staphylococcus aureus and Staphylococcus epidermidis are frequently associated with medical device infections that involve establishment of a bacterial biofilm on the device surface. Staphylococcal surface proteins Aap, SasG, and Pls are members of the Periscope Protein class and have been implicated in biofilm formation and host colonization; they comprise a repetitive region ("B region") and an N-terminal host colonization domain within the "A region," predicted to be a lectin domain. Repetitive E-G5 domains (as found in Aap, SasG, and Pls) form elongated "stalks" that would vary in length with repeat number, resulting in projection of the N-terminal A domain variable distances from the bacterial cell surface. Here, we present the structures of the lectin domains within A regions of SasG, Aap, and Pls and a structure of the Aap lectin domain attached to contiguous E-G5 repeats, suggesting the lectin domains will sit at the tip of the variable length rod. We demonstrate that these isolated domains (Aap, SasG) are sufficient to bind to human host desquamated nasal epithelial cells. Previously, proteolytic cleavage or a deletion within the A domain had been reported to induce biofilm formation; the structures suggest a potential link between these observations. Intriguingly, while the Aap, SasG, and Pls lectin domains bind a metal ion, they lack the nonproline cis peptide bond thought to be key for carbohydrate binding by the lectin fold. This suggestion of noncanonical ligand binding should be a key consideration when investigating the host cell interactions of these bacterial surface proteins.

Computerized adaptive test strategies for the matrix reasoning subtest of the Wechsler Adult Intelligence Scale, 4th Edition (WAIS-IV).

OBJECTIVE: Most neuropsychological tests were developed without the benefit of modern psychometric theory. We used item response theory (IRT) methods to determine whether a widely used test - the 26-item Matrix Reasoning subtest of the WAIS-IV - might be used more efficiently if it were administered using computerized adaptive testing (CAT). METHOD: Data on the Matrix Reasoning subtest from 2197 participants enrolled in the National Neuropsychology Network (NNN) were analyzed using a two-parameter logistic (2PL) IRT model. Simulated CAT results were generated to examine optimal short forms using fixed-length CATs of 3, 6, and 12 items and scores were compared to the original full subtest score. CAT models further explored how many items were needed to achieve a selected precision of measurement (standard error ≤ .40). RESULTS: The fixed-length CATs of 3, 6, and 12 items correlated well with full-length test results (with r = .90, .97 and .99, respectively). To achieve a standard error of .40 (approximate reliability = .84) only 3-7 items had to be administered for a large percentage of individuals. CONCLUSIONS: This proof-of-concept investigation suggests that the widely used Matrix Reasoning subtest of the WAIS-IV might be shortened by more than 70% in most examinees while maintaining acceptable measurement precision. If similar savings could be realized in other tests, the accessibility of neuropsychological assessment might be markedly enhanced, and more efficient time use could lead to broader subdomain assessment.

Periscope Proteins are variable-length regulators of bacterial cell surface interactions.

Changes at the cell surface enable bacteria to survive in dynamic environments, such as diverse niches of the human host. Here, we reveal "Periscope Proteins" as a widespread mechanism of bacterial surface alteration mediated through protein length variation. Tandem arrays of highly similar folded domains can form an elongated rod-like structure; thus, variation in the number of domains determines how far an N-terminal host ligand binding domain projects from the cell surface. Supported by newly available long-read genome sequencing data, we propose that this class could contain over 50 distinct proteins, including those implicated in host colonization and biofilm formation by human pathogens. In large multidomain proteins, sequence divergence between adjacent domains appears to reduce interdomain misfolding. Periscope Proteins break this "rule," suggesting that their length variability plays an important role in regulating bacterial interactions with host surfaces, other bacteria, and the immune system.

Evidence for Selection in the Abundant Accessory Gene Content of a Prokaryote Pangenome.

A pangenome is the complete set of genes (core and accessory) present in a phylogenetic clade. We hypothesize that a pangenome's accessory gene content is structured and maintained by selection. To test this hypothesis, we interrogated the genomes of 40 Pseudomonas species for statistically significant coincident (i.e., co-occurring/avoiding) gene patterns. We found that 86.7% of common accessory genes are involved in ≥1 coincident relationship. Further, genes that co-occur and/or avoid each other-but are not vertically inherited-are more likely to share functional categories, are more likely to be simultaneously transcribed, and are more likely to produce interacting proteins, than would be expected by chance. These results are not due to coincident genes being adjacent to one another on the chromosome. Together, these findings suggest that the accessory genome is structured into sets of genes that function together within a given strain. Given the similarity of the Pseudomonas pangenome with open pangenomes of other prokaryotic species, we speculate that these results are generalizable.

The long and the short of Periscope Proteins.

Bacteria sense, interact with, and modify their environmental niche by deploying a molecular ensemble at the cell surface. The changeability of this exposed interface, combined with extreme changes in the functional repertoire associated with lifestyle switches from planktonic to adherent and biofilm states necessitate dynamic variability. Dynamic surface changes include chemical modifications to the cell wall; export of diverse extracellular biofilm components; and modulation of expression of cell surface proteins for adhesion, co-aggregation and virulence. Local enrichment for highly repetitive proteins with high tandem repeat identity has been an enigmatic phenomenon observed in diverse bacterial species. Preliminary observations over decades of research suggested these repeat regions were hypervariable, as highly related strains appeared to express homologues with diverse molecular mass. Long-read sequencing data have been interrogated to reveal variation in repeat number; in combination with structural, biophysical and molecular dynamics approaches, the Periscope Protein class has been defined for cell surface attached proteins that dynamically expand and contract tandem repeat tracts at the population level. Here, I review the diverse high-stability protein folds and coherent interdomain linkages culminating in the formation of highly anisotropic linear repeat arrays, so-called rod-like protein 'stalks', supporting roles in bacterial adhesion, biofilm formation, cell surface spatial competition, and immune system modulation. An understanding of the functional impacts of dynamic changes in repeat arrays and broader characterisation of the unusual protein folds underpinning this variability will help with the design of immunisation strategies, and contribute to synthetic biology approaches including protein engineering and microbial consortia construction.

The Effectiveness of a Specialized Primary Care Medical Home for Patients with Serious Mental Illness.

BACKGROUND: There are unmet primary care needs among people with serious mental illness that might be improved with integrated care and medical care management. Many healthcare organizations have attempted to address this problem, but few interventions have been rigorously studied and found to be effective. OBJECTIVE: Study the implementation and effectiveness of a novel, specialized primary care medical home designed to improve the healthcare of patients with serious mental illness. DESIGN, SETTING, AND PARTICIPANTS: Clustered controlled trial for a median of 401 days. One Veterans Health Administration medical center was assigned to intervention and two were assigned to usual care (control). Thirty-nine clinicians and managers were included in the study, as well as 331 patients who met eligibility criteria. INTERVENTION: A specialized medical home with systematic patient engagement, proactive nurse panel management, a collaborative care psychiatrist, and a primary care physician providing care that included psychiatric treatment. MAIN MEASURES: Quality of care, chronic illness care and care experience, symptoms, and quality of life. KEY RESULTS: Sixty-five intervention patients (40%) moved all psychiatric care to the primary care team. No adverse events were attributable to the intervention. Compared with control, intervention patients had greater improvement over time in appropriate screening for body mass index, lipids, and glucose (χ2 = 6.9, 14.3, and 3.9; P's < .05); greater improvement in all domains of chronic illness care (activation, decision support, goal-setting, counseling, coordination) and care experience (doctor-patient interaction, shared decision-making, care coordination, access; F for each 10-24, P's < .05); and greater improvement in mental health-related quality of life (F = 3.9, P = .05) and psychotic symptoms (F = 3.9, P = .05). CONCLUSION: A primary care medical home for serious mental illness can be feasible to implement, safe, and more effective than usual care. TRIAL REGISTRATION: ClinicalTrials.gov Identifier: NCT01668355.

Rationale and Design of the National Neuropsychology Network.

OBJECTIVE: The National Neuropsychology Network (NNN) is a multicenter clinical research initiative funded by the National Institute of Mental Health (NIMH; R01 MH118514) to facilitate neuropsychology's transition to contemporary psychometric assessment methods with resultant improvement in test validation and assessment efficiency. METHOD: The NNN includes four clinical research sites (Emory University; Medical College of Wisconsin; University of California, Los Angeles (UCLA); University of Florida) and Pearson Clinical Assessment. Pearson Q-interactive (Q-i) is used for data capture for Pearson published tests; web-based data capture tools programmed by UCLA, which serves as the Coordinating Center, are employed for remaining measures. RESULTS: NNN is acquiring item-level data from 500-10,000 patients across 47 widely used Neuropsychology (NP) tests and sharing these data via the NIMH Data Archive. Modern psychometric methods (e.g., item response theory) will specify the constructs measured by different tests and determine their positive/negative predictive power regarding diagnostic outcomes and relationships to other clinical, historical, and demographic factors. The Structured History Protocol for NP (SHiP-NP) helps standardize acquisition of relevant history and self-report data. CONCLUSIONS: NNN is a proof-of-principle collaboration: by addressing logistical challenges, NNN aims to engage other clinics to create a national and ultimately an international network. The mature NNN will provide mechanisms for data aggregation enabling shared analysis and collaborative research. NNN promises ultimately to enable robust diagnostic inferences about neuropsychological test patterns and to promote the validation of novel adaptive assessment strategies that will be more efficient, more precise, and more sensitive to clinical contexts and individual/cultural differences.

Defining the remarkable structural malleability of a bacterial surface protein Rib domain implicated in infection.

Streptococcus groups A and B cause serious infections, including early onset sepsis and meningitis in newborns. Rib domain-containing surface proteins are found associated with invasive strains and elicit protective immunity in animal models. Yet, despite their apparent importance in infection, the structure of the Rib domain was previously unknown. Structures of single Rib domains of differing length reveal a rare case of domain atrophy through deletion of 2 core antiparallel strands, resulting in the loss of an entire sheet of the ß-sandwich from an immunoglobulin-like fold. Previously, observed variation in the number of Rib domains within these bacterial cell wall-attached proteins has been suggested as a mechanism of immune evasion. Here, the structure of tandem domains, combined with molecular dynamics simulations and small angle X-ray scattering, suggests that variability in Rib domain number would result in differential projection of an N-terminal host-colonization domain from the bacterial surface. The identification of 2 further structures where the typical B-D-E immunoglobulin ß-sheet is replaced with an α-helix further confirms the extensive structural malleability of the Rib domain.

Integrating Mental Health in Safety-net Primary Care: A Five-year Observational Study on Visits in a County Health System.

BACKGROUND: Beginning in 2010, Los Angeles County Departments of Health Services and Mental Health collaborated to increase access to effective mental health care. The Mental Health Integration Program (MHIP) embedded behavioral health specialists in primary care clinics to deliver brief, problem-focused treatments, and psychiatric consultation support for primary care-prescribed psychotropic medications. OBJECTIVE: The aim was to compare primary care visits associated with psychiatric diagnoses before and after MHIP implementation. METHODS: This retrospective cohort study (2009-2014) examined 62,945 patients from 8 safety-net clinics that implemented MHIP in a staggered manner in Los Angeles. Patients' primary care visits (n=695,354) were either associated or not with a previously identified or "new" (defined as having no diagnosis within the prior year) psychiatric diagnosis. Multilevel regression models used MHIP implementation to predict odds of visits being associated with psychiatric diagnoses, controlling for time, clinic, and patient characteristics. RESULTS: 9.4% of visits were associated with psychiatric diagnoses (6.4% depression, 3.1% anxiety, <1% alcohol, and substance use disorders). Odds of visits being associated with psychiatric diagnoses were 9% higher [95% confidence interval (CI)=1.05-1.13; P<0.0001], and 10% higher for diagnoses that were new (CI=1.04-1.16; P=0.002), after MHIP implementation than before. This appeared to be fueled by increased visits for depression post-MHIP (odds ratio=1.11; CI=1.06-1.15; P<0.0001). CONCLUSIONS: MHIP implementation was associated with more psychiatric diagnoses coded in safety-net primary care visits. Scaling up this effort will require greater attention to the notable differences across patient populations and languages, as well as the markedly low coding of alcohol and substance use services in primary care.

Disorder drives cooperative folding in a multidomain protein.

Many human proteins contain intrinsically disordered regions, and disorder in these proteins can be fundamental to their function-for example, facilitating transient but specific binding, promoting allostery, or allowing efficient posttranslational modification. SasG, a multidomain protein implicated in host colonization and biofilm formation in Staphylococcus aureus, provides another example of how disorder can play an important role. Approximately one-half of the domains in the extracellular repetitive region of SasG are intrinsically unfolded in isolation, but these E domains fold in the context of their neighboring folded G5 domains. We have previously shown that the intrinsic disorder of the E domains mediates long-range cooperativity between nonneighboring G5 domains, allowing SasG to form a long, rod-like, mechanically strong structure. Here, we show that the disorder of the E domains coupled with the remarkable stability of the interdomain interface result in cooperative folding kinetics across long distances. Formation of a small structural nucleus at one end of the molecule results in rapid structure formation over a distance of 10 nm, which is likely to be important for the maintenance of the structural integrity of SasG. Moreover, if this normal folding nucleus is disrupted by mutation, the interdomain interface is sufficiently stable to drive the folding of adjacent E and G5 domains along a parallel folding pathway, thus maintaining cooperative folding.

Major reorientation of tRNA substrates defines specificity of dihydrouridine synthases.

The reduction of specific uridines to dihydrouridine is one of the most common modifications in tRNA. Increased levels of the dihydrouridine modification are associated with cancer. Dihydrouridine synthases (Dus) from different subfamilies selectively reduce distinct uridines, located at spatially unique positions of folded tRNA, into dihydrouridine. Because the catalytic center of all Dus enzymes is conserved, it is unclear how the same protein fold can be reprogrammed to ensure that nucleotides exposed at spatially distinct faces of tRNA can be accommodated in the same active site. We show that the Escherichia coli DusC is specific toward U16 of tRNA. Unexpectedly, crystal structures of DusC complexes with tRNA(Phe) and tRNA(Trp) show that Dus subfamilies that selectively modify U16 or U20 in tRNA adopt identical folds but bind their respective tRNA substrates in an almost reverse orientation that differs by a 160° rotation. The tRNA docking orientation appears to be guided by subfamily-specific clusters of amino acids ("binding signatures") together with differences in the shape of the positively charged tRNA-binding surfaces. tRNA orientations are further constrained by positional differences between the C-terminal "recognition" domains. The exquisite substrate specificity of Dus enzymes is therefore controlled by a relatively simple mechanism involving major reorientation of the whole tRNA molecule. Such reprogramming of the enzymatic specificity appears to be a unique evolutionary solution for altering tRNA recognition by the same protein fold.

Streptococcus pneumoniae Colonization Is Required To Alter the Nasal Microbiota in Cigarette Smoke-Exposed Mice.

Smokers have nasal microbiota dysbiosis, with an increased frequency of colonizing bacterial pathogens. It is possible that cigarette smoke increases pathogen acquisition by perturbing the microbiota and decreasing colonization resistance. However, it is difficult to disentangle microbiota dysbiosis due to cigarette smoke exposure from microbiota changes caused by increased pathogen acquisition in human smokers. Using an experimental mouse model, we investigated the impact of cigarette smoke on the nasal microbiota in the absence and presence of nasal pneumococcal colonization. We observed that cigarette smoke exposure alone did not alter the nasal microbiota composition. The microbiota composition was also unchanged at 12 h following low-dose nasal pneumococcal inoculation, suggesting that the ability of the microbiota to resist initial nasal pneumococcal acquisition was not impaired in smoke-exposed mice. However, nasal microbiota dysbiosis occurred as a consequence of established high-dose nasal pneumococcal colonization at day 3 in smoke-exposed mice. Similar to clinical reports on human smokers, an enrichment of potentially pathogenic bacterial genera such as Fusobacterium, Gemella, and Neisseria was observed. Our findings suggest that cigarette smoke exposure predisposes to pneumococcal colonization independent of changes to the nasal microbiota and that microbiota dysbiosis observed in smokers may occur as a consequence of established pathogen colonization.

Partitioning and correlating subgroup characteristics from Aligned Pattern Clusters.

MOTIVATION: Evolutionarily conserved amino acids within proteins characterize functional or structural regions. Conversely, less conserved amino acids within these regions are generally areas of evolutionary divergence. A priori knowledge of biological function and species can help interpret the amino acid differences between sequences. However, this information is often erroneous or unavailable, hampering discovery with supervised algorithms. Also, most of the current unsupervised methods depend on full sequence similarity, which become inaccurate when proteins diverge (e.g. inversions, deletions, insertions). Due to these and other shortcomings, we developed a novel unsupervised algorithm which discovers highly conserved regions and uses two types of information measures: (i) data measures computed from input sequences; and (ii) class measures computed using a priori class groupings in order to reveal subgroups (i.e. classes) or functional characteristics. RESULTS: Using known and putative sequences of two proteins belonging to a relatively uncharacterized protein family we were able to group evolutionarily related sequences and identify conserved regions, which are strong homologous association patterns called Aligned Pattern Clusters, within individual proteins and across the members of this family. An initial synthetic demonstration and in silico results reveal that (i) the data measures are unbiased and (ii) our class measures can accurately rank the quality of the evolutionarily relevant groupings. Furthermore, combining our data and class measures allowed us to interpret the results by inferring regions of biological importance within the binding domain of these proteins. Compared to popular supervised methods, our algorithm has a superior runtime and comparable accuracy. AVAILABILITY AND IMPLEMENTATION: The dataset and results are available at www.pami.uwaterloo.ca/∼ealee/files/classification2015 CONTACT: akcwong@uwaterloo.ca SUPPLEMENTARY INFORMATION: Supplementary data are available at Bioinformatics online.

Improving Weight in People with Serious Mental Illness: The Effectiveness of Computerized Services with Peer Coaches.

BACKGROUND: People with serious mental illness have high rates of obesity and related medical problems, and die years prematurely, most commonly from cardiovascular disease. Specialized, in-person weight management interventions result in weight loss in efficacy trials with highly motivated patients. In usual care, patient enrollment and retention are low with these interventions, and effectiveness has been inconsistent. OBJECTIVE: To determine whether computerized provision of weight management with peer coaching is feasible to deliver, is acceptable to patients, and is more effective than in-person delivery or usual care. DESIGN: Mixed-methods randomized controlled trial. PARTICIPANTS: Two hundred seventy-six overweight patients with serious mental illness receiving care at a Veterans Administration medical center. INTERVENTIONS: Patients were randomized to 1) computerized weight management with peer coaching (WebMOVE), 2) in-person clinician-led weight services, or 3) usual care. Both active interventions offered the same educational content. MAIN MEASURES: Body mass index; and feasibility and acceptability of the intervention. KEY RESULTS: At 6 months, in obese patients (n = 200), there was a significant condition by visit effect (F = 4.02, p = 0.02). The WebMOVE group had an average estimated BMI change from baseline to 6 months of 34.9 ± 0.4 to 34.1 ± 0.4. This corresponds to 2.8 kg (6.2 lbs) weight loss (t = 3.2, p = 0.001). No significant change in BMI was seen with either in-person services (t = 0.10, p = 0.92), or usual care (t = -0.25, p = 0.80). The average percentage of modules completed in the WebMOVE group was 49% and in the in-person group was 41% (t = 1.4, p = 0.17). When non-obese patients were included in the analyses, there was a trend towards a condition by visit effect (F = 2.8, p = 0.06). WebMOVE was well received, while the acceptability of in-person services was mixed. CONCLUSIONS: Computerized weight management with peer support results in lower weight, and can have greater effectiveness than clinician-led in-person services. This intervention is well received, and could be feasible to disseminate.

Structural basis for DNA strand separation by a hexameric replicative helicase.

Hexameric helicases are processive DNA unwinding machines but how they engage with a replication fork during unwinding is unknown. Using electron microscopy and single particle analysis we determined structures of the intact hexameric helicase E1 from papillomavirus and two complexes of E1 bound to a DNA replication fork end-labelled with protein tags. By labelling a DNA replication fork with streptavidin (dsDNA end) and Fab (5' ssDNA) we located the positions of these labels on the helicase surface, showing that at least 10 bp of dsDNA enter the E1 helicase via a side tunnel. In the currently accepted 'steric exclusion' model for dsDNA unwinding, the active 3' ssDNA strand is pulled through a central tunnel of the helicase motor domain as the dsDNA strands are wedged apart outside the protein assembly. Our structural observations together with nuclease footprinting assays indicate otherwise: strand separation is taking place inside E1 in a chamber above the helicase domain and the 5' passive ssDNA strands exits the assembly through a separate tunnel opposite to the dsDNA entry point. Our data therefore suggest an alternative to the current general model for DNA unwinding by hexameric helicases.

Clinical Factors Associated with Successful Discharge from Assertive Community Treatment.

We sought to explore clinical factors associated with successful transition from Assertive Community Treatment to less intensive clinical services. Mixed-method observational follow up study of veterans discharged from three VA-affiliated ACT teams to less intensive clinical services. Of the 240 veterans in ACT, 9% (n = 21) were discharged during the study period. Among the 11 of 21 discharged veterans who enrolled in the follow up study, reason for discharge, designated by the veteran's primary clinician at the time of discharge, predicted outcomes (p = 0.02) at 9 months, with "disengagement" as a reason for discharge predicting poorer outcomes. Six of 11 veterans experienced poor outcomes at 9 months, including incarceration and substance use relapse. ACT clinicians rarely discharge clients. Many clients may experience negative clinical events following ACT discharge, and clients may be difficult to follow post-discharge. Client disengagement from ACT may indicate higher likelihood of poor outcomes following discharge to less intensive clinical services.

Streptococcus pneumoniae Colonization Disrupts the Microbial Community within the Upper Respiratory Tract of Aging Mice.

Nasopharyngeal colonization by the Gram-positive bacterium Streptococcus pneumonia is a prerequisite for pneumonia and invasive pneumococcal diseases. Colonization is asymptomatic, involving dynamic and complex interplay between commensals, the host immune system, and environmental factors. The elderly are at an increased risk of developing pneumonia, which might be due to changes in the respiratory microbiota that would impact bacterial colonization and persistence within this niche. We hypothesized that the composition of the upper respiratory tract (URT) microbiota changes with age and subsequently can contribute to sustained colonization and inefficient clearance of S. pneumoniae To test this, we used a mouse model of pneumococcal colonization to compare the composition of the URT microbiota in young, middle-aged, and old mice in the naive state and during the course of colonization using nasal pharyngeal washes. Sequencing of variable region 3 (V3) of the 16S rRNA gene was used to identify changes occurring with age and throughout the course of S. pneumonia colonization. We discovered that age affects the composition of the URT microbiota and that colonization with S. pneumoniae is more disruptive of preexisting communities in older mice. We have further shown that host-pathogen interactions followingS. pneumonia colonization can impact the populations of resident microbes, including Staphylococcus and Haemophilus. Together, our findings indicate alterations to the URT microbiota could be detrimental to the elderly, resulting in increased colonization of S. pneumonia and decreased efficiency in its clearance.

From bacterial to human dihydrouridine synthase: automated structure determination.

The reduction of uridine to dihydrouridine at specific positions in tRNA is catalysed by dihydrouridine synthase (Dus) enzymes. Increased expression of human dihydrouridine synthase 2 (hDus2) has been linked to pulmonary carcinogenesis, while its knockdown decreased cancer cell line viability, suggesting that it may serve as a valuable target for therapeutic intervention. Here, the X-ray crystal structure of a construct of hDus2 encompassing the catalytic and tRNA-recognition domains (residues 1-340) determined at 1.9 Šresolution is presented. It is shown that the structure can be determined automatically by phenix.mr_rosetta starting from a bacterial Dus enzyme with only 18% sequence identity and a significantly divergent structure. The overall fold of the human Dus2 is similar to that of bacterial enzymes, but has a larger recognition domain and a unique three-stranded antiparallel ß-sheet insertion into the catalytic domain that packs next to the recognition domain, contributing to domain-domain interactions. The structure may inform the development of novel therapeutic approaches in the fight against lung cancer.

Two repetitive, biofilm-forming proteins from Staphylococci: from disorder to extension.

Staphylococcus aureus and Staphylococcus epidermidis are an important cause of medical device-related infections that are difficult to treat with antibiotics. Biofilms, in which bacteria are embedded in a bacterially-produced exopolymeric matrix, form on the surface of the implanted medical device. Our understanding of the molecular mechanisms underlying the initial surface attachment and subsequent intercellular interactions as the biofilm matures is improving. Biofilm accumulation can be mediated by a partially deacetylated form of poly-N-acetylglucosamine (PNAG) but, more recently, the role of bacterial surface proteins is being recognized. Here we describe the structure and function of two S. aureus cell surface proteins, FnBPA and SasG, implicated in host interactions and biofilm accumulation. These multifunctional proteins employ intrinsic disorder for distinct molecular outcomes. In the case of FnBPA, disorder generates adhesive arrays that bind fibronectin (Fn); in the case of SasG, disorder is, counterintuitively, used to maintain a strong extended fold.

A flexible brace maintains the assembly of a hexameric replicative helicase during DNA unwinding.

The mechanism of DNA translocation by papillomavirus E1 and polyomavirus LTag hexameric helicases involves consecutive remodelling of subunit-subunit interactions around the hexameric ring. Our biochemical analysis of E1 helicase demonstrates that a 26-residue C-terminal segment is critical for maintaining the hexameric assembly. As this segment was not resolved in previous crystallographic analysis of E1 and LTag hexameric helicases, we determined the solution structure of the intact hexameric E1 helicase by Small Angle X-ray Scattering. We find that the C-terminal segment is flexible and occupies a cleft between adjacent subunits in the ring. Electrostatic potential calculations indicate that the negatively charged C-terminus can bridge the positive electrostatic potentials of adjacent subunits. Our observations support a model in which the C-terminal peptide serves as a flexible 'brace' maintaining the oligomeric state during conformational changes associated with ATP hydrolysis. We argue that these interactions impart processivity to DNA unwinding. Sequence and disorder analysis suggest that this mechanism of hexamer stabilization would be conserved among papillomavirus E1 and polyomavirus LTag hexameric helicases.