Profiling Ssb-Nascent Chain Interactions Reveals Principles of Hsp70-Assisted Folding.

The yeast Hsp70 chaperone Ssb interacts with ribosomes and nascent polypeptides to assist protein folding. To reveal its working principle, we determined the nascent chain-binding pattern of Ssb at near-residue resolution by in vivo selective ribosome profiling. Ssb associates broadly with cytosolic, nuclear, and hitherto unknown substrate classes of mitochondrial and endoplasmic reticulum (ER) nascent proteins, supporting its general chaperone function. Ssb engages most substrates by multiple binding-release cycles to a degenerate sequence enriched in positively charged and aromatic amino acids. Timely association with this motif upon emergence at the ribosomal tunnel exit requires ribosome-associated complex (RAC) but not nascent polypeptide-associated complex (NAC). Ribosome footprint densities along orfs reveal faster translation at times of Ssb binding, mainly imposed by biases in mRNA secondary structure, codon usage, and Ssb action. Ssb thus employs substrate-tailored dynamic nascent chain associations to coordinate co-translational protein folding, facilitate accelerated translation, and support membrane targeting of organellar proteins.

Nascent Polypeptide Domain Topology and Elongation Rate Direct the Cotranslational Hierarchy of Hsp70 and TRiC/CCT.

Cotranslational protein folding requires assistance from elaborate ribosome-associated chaperone networks. It remains unclear how the changing information in a growing nascent polypeptide dictates the recruitment of functionally distinct chaperones. Here, we used ribosome profiling to define the principles governing the cotranslational action of the chaperones TRiC/CCT and Hsp70/Ssb. We show that these chaperones are sequentially recruited to specific sites within domain-encoding regions of select nascent polypeptides. Hsp70 associates first, binding select sites throughout domains, whereas TRiC associates later, upon the emergence of nearly complete domains that expose an unprotected hydrophobic surface. This suggests that transient topological properties of nascent folding intermediates drive sequential chaperone association. Moreover, cotranslational recruitment of both TRiC and Hsp70 correlated with translation elongation slowdowns. We propose that the temporal modulation of the nascent chain structural landscape is coordinated with local elongation rates to regulate the hierarchical action of Hsp70 and TRiC for cotranslational folding.

Molecular insights into the prototypical single-stranded DNA-binding protein from E. coli.

The SSB protein of Escherichia coli functions to bind single-stranded DNA wherever it occurs during DNA metabolism. Depending upon conditions, SSB occurs in several different binding modes. In the course of its function, SSB diffuses on ssDNA and transfers rapidly between different segments of ssDNA. SSB interacts with many other proteins involved in DNA metabolism, with 22 such SSB-interacting proteins, or SIPs, defined to date. These interactions chiefly involve the disordered and conserved C-terminal residues of SSB. When not bound to ssDNA, SSB can aggregate to form a phase-separated biomolecular condensate. Current understanding of the properties of SSB and the functional significance of its many intermolecular interactions are summarized in this review.

Improved prediction of DNA and RNA binding proteins with deep learning models.

Nucleic acid-binding proteins (NABPs), including DNA-binding proteins (DBPs) and RNA-binding proteins (RBPs), play important roles in essential biological processes. To facilitate functional annotation and accurate prediction of different types of NABPs, many machine learning-based computational approaches have been developed. However, the datasets used for training and testing as well as the prediction scopes in these studies have limited their applications. In this paper, we developed new strategies to overcome these limitations by generating more accurate and robust datasets and developing deep learning-based methods including both hierarchical and multi-class approaches to predict the types of NABPs for any given protein. The deep learning models employ two layers of convolutional neural network and one layer of long short-term memory. Our approaches outperform existing DBP and RBP predictors with a balanced prediction between DBPs and RBPs, and are more practically useful in identifying novel NABPs. The multi-class approach greatly improves the prediction accuracy of DBPs and RBPs, especially for the DBPs with ~12% improvement. Moreover, we explored the prediction accuracy of single-stranded DNA binding proteins and their effect on the overall prediction accuracy of NABP predictions.

The convergence of head-on DNA unwinding forks induces helicase oligomerization and activity transition.

Helicases are multifunctional motor proteins with the primary task of separating nucleic acid duplexes. These enzymes often exist in distinct oligomeric forms and play essential roles during nucleic acid metabolism. Whether there is a correlation between their oligomeric state and cellular function, and how helicases effectively perform functional switching remains enigmatic. Here, we address these questions using a combined single-molecule approach and Bloom syndrome helicase (BLM). By examining the head-on collision of two BLM-mediated DNA unwinding forks, we find that two groups of BLM, upon fork convergence, promptly oligomerize across the fork junctions and tightly bridge two independent single-stranded (ss) DNA molecules that were newly generated by the unwinding BLMs. This protein oligomerization is mediated by the helicase and RNase D C-terminal (HRDC) domain of BLM and can sustain a disruptive force of up to 300 pN. Strikingly, onsite BLM oligomerization gives rise to an immediate transition of their helicase activities, from unwinding dsDNA to translocating along ssDNA at exceedingly fast rates, thus allowing for the efficient displacement of ssDNA-binding proteins, such as RPA and RAD51. These findings uncover an activity transition pathway for helicases and help to explain how BLM plays both pro- and anti-recombination roles in the maintenance of genome stability.

Bacterial nucleoid is a riddle wrapped in a mystery inside an enigma.

Bacterial chromosome, the nucleoid, is traditionally modeled as a rosette of DNA mega-loops, organized around proteinaceous central scaffold by nucleoid-associated proteins (NAPs), and mixed with the cytoplasm by transcription and translation. Electron microscopy of fixed cells confirms dispersal of the cloud-like nucleoid within the ribosome-filled cytoplasm. Here, I discuss evidence that the nucleoid in live cells forms DNA phase separate from riboprotein phase, the "riboid." I argue that the nucleoid-riboid interphase, where DNA interacts with NAPs, transcribing RNA polymerases, nascent transcripts, and ssRNA chaperones, forms the transcription zone. An active part of phase separation, transcription zone enforces segregation of the centrally positioned information phase (the nucleoid) from the surrounding action phase (the riboid), where translation happens, protein accumulates, and metabolism occurs. I speculate that HU NAP mostly tiles up the nucleoid periphery-facilitating DNA mobility but also supporting transcription in the interphase. Besides extruding plectonemically supercoiled DNA mega-loops, condensins could compact them into solenoids of uniform rings, while HU could support rigidity and rotation of these DNA rings. The two-phase cytoplasm arrangement allows the bacterial cell to organize the central dogma activities, where (from the cell center to its periphery) DNA replicates and segregates, DNA is transcribed, nascent mRNA is handed over to ribosomes, mRNA is translated into proteins, and finally, the used mRNA is recycled into nucleotides at the inner membrane. The resulting information-action conveyor, with one activity naturally leading to the next one, explains the efficiency of prokaryotic cell design-even though its main intracellular transportation mode is free diffusion.

High-risk groups of neonatal lupus erythematosus in term infants: a birth cohort study.

This study aims to analyze the clinical characteristics and risk factors of high-risk groups of neonatal lupus erythematosus (NLE) in term infants. High-risk groups of NLE infants whose mothers were positive for anti-SSA, anti-SSB or anti-U1RNP antibodies during pregnancy were enrolled. They were born between February 2013 and February 2020, with a gestational age not less than 37 weeks. We analyzed their clinical data from birth to 24 months after birth. A total of 105 patients in the NLE high-risk group were included. Among them, 30 patients were diagnosed with NLE (NLE group), and 75 patients were not (non-NLE group). The affected systems of the NLE group included the dermal (13.3%), hepatic (76.0%), and hematological systems (43.3%). Hepatic involvement, anemia and thrombocytopenia did not emerge until 60 days, 41 days and 22 days after birth, respectively, in some cases. Systemic involvement could be cured within 3 to 12 months after birth. The clearance time of specific autoantibodies was 12 months after birth. There was no significant difference in the clinical characteristics of babies and their mothers between the two groups, neither in the positive rate nor in the clearance time of specific autoantibodies. CONCLUSION: After standardized prenatal health care, there is still a high risk of dermal, hepatic, or hematological system involvement for high-risk groups of NLE. There are no specific indicators for the prediction of whether babies will develop NLE. All of these patients need to be followed up closely within one year after birth. WHAT IS KNOWN: • Neonatal lupus erythematosus (NLEs) can affect the cardiac, dermal, hepatic, and hematological systems of infants. WHAT IS NEW: • After standardized prenatal health care employing good multidepartment cooperation in our center, no neonates had cardiac block in this study. However, dermal, hepatic, and hematological system involvement of NLE can still gradually appear (as long as 60 days after birth in some cases) during follow-up, and some of these conditions are serious and require timely and active intervention. No single factor has been found to predict whether offspring at high-risk of NLE whose mothers are positive for anti-SSA, SSB and/or RNP will develop NLE.

Sjogren's syndrome due to immune checkpoint inhibitors (ICIs): Insights from a single-institution series and systematic review of the literature.

INTRODUCTION: Careful adverse event assessment and management are important when prescribing immune checkpoint inhibitors (ICIs) to cancer patients. Iatrogenic Sjogren's syndrome is a relatively rare immune-related adverse event (irAEs) that affects the moisture-producing glands. METHODS: We describe a series of four patients who developed Sjogren's syndrome while being treated with ICIs at a community cancer center in Southern California, USA (1/1/2017-12/31/2023). Patient, drug and disease-related data were collected by retrospective chart review. A systematic search of the PubMed database was performed to identify similar cases in the literature (1/1/2016-12/31//2023). RESULTS: Of 224 cancer patients at our center treated with ICIs, four (1.8%) developed iatrogenic Sjogren's syndrome. All of our patients were male; three received PD-1 inhibitors (nivolumab, pembrolizumab) and one received the PD-L1 inhibitor atezolizumab. The median time to development of Sjogren's syndrome was 24 weeks (range, 8-36 weeks); dry mouth symptoms were more prominent than dry eye symptoms. None of the patients had elevated SS-A, SS-B or antinuclear antibodies. One patient developed multiple tooth cavities and had several extractions, due to severe xerostomia. Management of all patients was primarily symptomatic. Two cases were irreversible; one was reversible and the 4th case is undermined as he is still on ICI therapy. Our systematic review of the literature identified 80 cases in five articles. Incidence of xerostomia was twice of that of xerophthalmia. The male/female ratio was 1.5:1. SS-A, SS-B, or antinuclear antibodies were found in only 9% of patients. Steroids were reported to have had only a limited role in management. CONCLUSIONS: The incidence of Sjogren's syndrome due to ICIs in our center was 1.8%. Details of clinical course and management in these patients are presented. Caring for patients with ICI-related Sjogren's syndrome is facilitated by a multidisciplinary effort including oncologists, otolaryngologists, dentists, ophthalmologists and rheumatologists. Expanding the knowledge base pertaining to iatrogenic Sjogren's syndrome in patients on ICIs will be helpful in promoting early detection and treatment, and improving outcomes.

Shoulder balloon spacer for massive irreparable rotator cuff tears results in significant improvements.

PURPOSE: The aim of the present study was to assess the effectiveness of balloon implantation in patients with irreparable supraspinatus tears alone or in combination with other rotator cuff (RC) tendon tears and the effect of several covariables, such as age, gender, status of the long head biceps, with or without tendon repair and regardless the number of tendon involved. METHODS: Patients enrolled from 'San Carlo' Hospital of Potenza (Italy, IT), from January 2012 to September 2014, underwent arthroscopic implantation of shoulder balloon by a single surgeon, and followed for 3 years. The American Shoulder and Elbow Surgeons (ASES) and Constant score (CS) were administered pre-, post-operatively at 12 months, and then annually. Patients were classified on the basis of the number of tendons involved in the tears and treatment performed, considering the reparability of the tendons themselves. Gleno-humeral joint osteoarthrosis (OA) was evaluated through shoulder radiographs and classified according to the Samilson-Prieto classification, at the first examination and at the final follow-up. Statistical improvements were evaluated using a variance model (least-squares means) and a T distribution test for the evaluation between different treatment groups. RESULTS: A total of 61 procedures were performed, and eight patients were lost during follow-up. The mean baseline CS was 30.2 ± 15.4 with statistically significant improvement, respectively, at 1-, 2- and 3-year follow-up to 69.3 ± 4.2, 74.6 ± 3.6 and 69.7 ± 5.1 respectively. ASES score at baseline was 22.5 ± 10.9, with a statistically significant improvement to 69.7 ± 9.2, 68 ± 17.8 and 71.2 ± 16.6 at 1-, 2- and 3-year follow-up, respectively. Tenotomy or absence of long head biceps at presentation did not influence results (n.s.), with no difference according to gender and age. At final follow-up, 24 patients (43.9%) showed progression of glenohumeral OA. One patient required secondary surgery for shoulder replacement after 18 months for persistent pain and one patient required implant removal following post-operative laser treatment. CONCLUSION: Arthroscopic rotator cuff tears repair with subacromial spacer balloon implantation showed statistically significant clinical and functional improvement at 3-year follow-up. Patients treated with combined partial repair and subacromial spacer balloon implantation experienced good results independent of gender, age, type of tear and long-head biceps tendon status. The risks related to this procedure appear to be minimal. LEVEL OF EVIDENCE: Level IV.

Binding Pattern and Structural Interactome of the Anticancer Drug 5-Fluorouracil: A Critical Review.

5-Fluorouracil (5-FU) stands as one of the most widely prescribed chemotherapeutics. Despite over 60 years of study, a systematic synopsis of how 5-FU binds to proteins has been lacking. Investigating the specific binding patterns of 5-FU to proteins is essential for identifying additional interacting proteins and comprehending their medical implications. In this review, an analysis of the 5-FU binding environment was conducted based on available complex structures. From the earliest complex structure in 2001 to the present, two groups of residues emerged upon 5-FU binding, classified as P- and R-type residues. These high-frequency interactive residues with 5-FU include positively charged residues Arg and Lys (P type) and ring residues Phe, Tyr, Trp, and His (R type). Due to their high occurrence, 5-FU binding modes were simplistically classified into three types, based on interactive residues (within <4 Å) with 5-FU: Type 1 (P-R type), Type 2 (P type), and Type 3 (R type). In summary, among 14 selected complex structures, 8 conform to Type 1, 2 conform to Type 2, and 4 conform to Type 3. Residues with high interaction frequencies involving the N1, N3, O4, and F5 atoms of 5-FU were also examined. Collectively, these interaction analyses offer a structural perspective on the specific binding patterns of 5-FU within protein pockets and contribute to the construction of a structural interactome delineating the associations of the anticancer drug 5-FU.

Life, the genome and everything.

In this issue of the Journal of Bacteriology, N. J. Bonde, E. A. Wood, K. S. Myers, M. Place, J. L. Keck, and M. M. Cox (J Bacteriol 205:e00184-23, 2023, https//doi.org/10.1128/jb.00184-23) used an unbiased transposon-sequencing (Tn-seq) screen to identify proteins required for life when cells lose the RecG branched-DNA helicase (synthetic lethality). The proteins' identities indicate pathways that prevent endogenous DNA damage, pathways that prevent its homology-directed repair (HDR) "strand-exchange" intermediates between sister chromosomes, and pathways that resolve those intermediates. All avoid intermediate pile-up, which blocks chromosome segregation, causing "death-by-recombination." DNA damage is managed to regulate crucial but potentially lethal HDR.

Protein-protein association properties of human ßB2-crystallins.

Protein-protein association events are involved in many physiological and pathological processes. Cataract disease is a pathology that manifests protein aggregation of crystallins. ß-Crystallins are present in a high proportion in the eye lens. Therefore, the structural study of the dimerization properties of crystallins can shed light on the first stages of protein aggregation. In the present work, we examine the protein-protein association profiles of the human ßB2-crystallin by employing extensive coarse-grained molecular dynamics (CG-MD) and the Markov state analysis. Interestingly, our results clearly show important changes in the protein dimerization kinetics between wt-HßB2C and the deamidated systems. The two systems show dimeric conformations. However, the association and dissociation rates are very different. Our results show that the deamidated system can associate faster and dissociate slower than the wt- HßB2C. The deamidated system is in a slightly opened conformation with the Greek-key motifs well folded, suggesting that a complete unfolding of the protein is not required for aggregation. Our results describe the first stages of crystallin aggregation due to post-translational modifications.

Zuo1, a ribosome-associated J protein, is involved in glucose repression in Saccharomyces cerevisiae.

In Saccharomyces cerevisiae, the J-protein Zuo1 and the nonconventional Hsp70 homologue Ssz1 stimulate the ATPase activity of the chaperone proteins Ssb1 and Ssb2 (Ssb1/2), which are associated with the ribosomes. The dephosphorylation of sucrose nonfermenting 1 (Snf1) on Thr210 is required for glucose repression. The Ssb1/2 and 14-3-3 proteins Bmh1 and Bmh2 appear to be responsible for the dephosphorylation of Snf1 on Thr210 and glucose repression. Here, we investigated the role of Zuo1 in glucose repression. The zuo1∆ strain as well as the ssb1∆ssb2∆ strain exhibited a glucose-specific growth defect during logarithmic growth on glucose. Many of the respiratory chain genes examined were statistically significantly upregulated, but less than 2-fold, in the zuo1∆ strain as well as in the ssb1∆ssb2∆ strain on glucose. In addition, excessive phosphorylation of Snf1 on Thr210 was observed in the zuo1∆ strain as well as in the ssb1∆ssb2∆ strain in the presence of glucose. The mRNA levels of SSB1/2 and BMH1 were statistically significantly reduced by approximately 0.5- to 0.8-fold relative to the wild-type level in the zuo1∆ strain on glucose. These results suggest that Zuo1 is responsible for glucose repression, possibly by increasing the mRNA levels of SSB1/2 and BMH1 during growth on glucose.

The association between autoantibody types and salivary gland hypofunction in patients with primary Sjögren's syndrome.

BACKGROUND: This study analyzed the association between autoantibody types and salivary gland hypofunction in patients with primary Sjögren's syndrome (pSS). METHODS: A retrospective analysis was performed on patients who visited the Department of Orofacial Pain and Oral Medicine at Yonsei University Dental Hospital from January 1, 2010 to May 31, 2021, and who were diagnosed with pSS. Out of 191 patients who fulfilled the 2016 American College of Rheumatology/European League Against Rheumatism classification criteria, 50 were positive for both anti-Ro/SSA and anti-La/SSB, whereas 97 had anti-Ro/SSA but not anti-La/SSB antibodies. Forty-four patients for whom neither anti-Ro/SSA nor anti-La/SSB antibodies were found were diagnosed with Sjögren's syndrome by minor salivary gland biopsy. RESULTS: The anti-Ro/SSA antibody-positive group showed higher rheumatoid factor (RF) levels than the anti-Ro/SSA antibody-negative group. The anti-La/SSB antibody-positive group showed lower unstimulated whole saliva (UWS), stimulated whole saliva (SWS), higher erythrocyte sedimentation rate and RF level than the anti-La/SSB antibody-negative group. In addition, the group with both anti-Ro/SSA and anti-La/SSB antibodies showed lower UWS than the group with only anti-Ro/SSA antibodies. However, there were no significant differences in UWS or SWS after taking pilocarpine, and C-reactive protein. CONCLUSIONS: UWS and SWS were lower when a patient was positive for anti-La/SSB, showing that anti-La/SSB is more likely to be involved in salivary gland hypofunction than anti-Ro/SSA in patients with pSS. Therefore, performing laboratory tests, including anti-La/SSB, helps predict the prognosis of salivary gland function in patients with suspected pSS.

Is evoking fear effective? Exploratory findings from a randomised experiment on the impacts of health warning labels on sugar-sweetened beverages.

OBJECTIVE: Health warning labels (HWL) have been suggested to be effective in reducing consumption of sugar-sweetened beverages (SSB). Yet, the efficacy and acceptability of SSB HWL of different formats (textual/pictorial) and severity remain unclear. This exploratory study aims to examine the extent and mechanism through which HWL of different formats and severity may affect responses towards the HWL and SSB consumption. DESIGN: Randomised online experiment. Participants were exposed to images of a hypothetical SSB bearing a HWL of one of three conditions: text-only HWL, moderately severe pictorial HWL and highly severe pictorial HWL. They then responded to theory-based affective, cognitive and behavioural measures. SETTING: Singapore. PARTICIPANTS: One hundred and twenty-seven young adult consumers from a public university. RESULTS: Direct effects were found for fear, avoidance, reactance and acceptability of the HWL, but not attitude, intention or motivation to consume less SSB. Pictorial (moderately severe and highly severe) HWL were associated with greater fear, avoidance, and reactance, and lower acceptability than text-only HWL. There was weak evidence that highly severe pictorial HWL resulted in greater reactance than moderately severe pictorial HWL. Fear mediated the effect of HWL of different severity levels on avoidance, reactance, intention and motivation, but not for attitude or acceptability. CONCLUSIONS: Exploratory findings indicate that although pictorial HWL were less acceptable, they may still be effective in influencing intention and motivation to reduce SSB consumption through the psychological mechanism of fear. Hence, graphic HWL should not be dismissed too quickly when considering strategies for reducing SSB consumption.

School health promotion and the consumption of water and sugar-sweetened beverages in secondary schools: a cross-sectional multilevel study.

BACKGROUND: Overweight among adolescents remains a serious concern worldwide and can have major health consequences in later life, such as cardiovascular diseases and cancer. Still, 33% of secondary school adolescents in the Netherlands consume sugar-sweetened beverages daily and over 26% do not consume water every day. The Dutch Healthy School program was developed to support schools in stimulating healthier lifestyles by focusing on health education, school environments, identifying students' health problems, and school policy. We examined the variation between secondary schools regarding the daily consumption of water and sugar-sweetened beverages and whether this variation can be explained by differences between schools regarding Healthy School certification, general school characteristics, and the school population. METHODS: We performed a cross-sectional multilevel study. We used data from the national Youth Health Monitor of 2019 on secondary schools (grades 8 and 10, age range about 12 to 18 years) of seven Public Health Services and combined these with information regarding Healthy School certification and general school- and school population characteristics. Our outcomes were daily consumption of water and sugar-sweetened beverages. In total, data from 51,901 adolescents from 191 schools were analysed. We calculated the intraclass correlation to examine the variation between schools regarding our outcomes. Thereafter, we examined whether we could explain this variation by the included characteristics. RESULTS: The school-level explained 4.53% of the variation in the consumption of water and 2.33% of the variation in the consumption of sugar-sweetened beverages. This small variation in water and sugar-sweetened consumption could not be explained by Healthy School certification, yet some general school- and school population characteristics did: the proportion of the school population with at least one parent with high educational attainment, the educational track of the adolescents, urbanicity (only for water consumption) and school type (only for sugar-sweetened beverages consumption). CONCLUSIONS: The low percentages of explained variation indicate that school-level characteristics in general (including Healthy School certification) do not matter substantially for the daily consumption of water and sugar-sweetened beverages. Future research should examine whether school health promotion can contribute to healthier lifestyles, and if so, under which level of implementation and school conditions.

The crowding-out effect of sugar-sweetened beverages (SSBs) on household expenditure patterns in Bangladesh.

BACKGROUND: Consumption of sugar-sweetened beverages (SSBs) or sugary drinks may reduce or even eliminate the household income allocation for other essential commodities. Reducing expenditure for consumption of other household commodities is known as the crowding-out effect of SSB. We aimed to determine the crowding-out effect of SSB expenditure on other household commodities. In addition, we also identified the factors influencing the household's decision to purchase of SSBs. METHODS: We used the logistic regression (logit and multinomial logit models) and the Seemingly Unrelated Regression (SUR) models. In order to find the probability of a given change in the socio-demographic variables, we also estimated the average marginal effects from the logistic regression. In addition, we regressed the SUR model by gender differences. We used Household Income and Expenditure Survey (HIES) 2016 data to estimate our chosen econometric models. HIES is nationally representative data on the household level across the country and is conducted using a multistage random sampling method by covering 46,075 households. RESULTS: The findings from the logit model describe that the greater proportion of male members, larger household size, household heads with higher education, profession, having a refrigerator, members living outside of the house, and households with higher income positively affect the decision of purchasing SSB. However, the determinants vary with the various types of SSB. The unadjusted crowding out effect shows that expenditure on SSB or sugar-added drinks crowds out the household expenditure on food, clothing, housing, and energy items. On the other hand, the adjusted crowding out effect crowds out the spending on housing, education, transportation, and social and state responsibilities. CONCLUSION: Although the household expenditure on beverages and sugar-added drinks is still moderate (around 2% of monthly household expenditure), the increased spending on beverages and sugar-added drinks is a concern due to the displacement of household expenditure for basic commodities such as food, clothing, housing, education, and energy. Therefore, evidence-based policies to regulate the sale and consumption of SSB are required for a healthy nation.

Normal levels of ribosome-associated chaperones cure two groups of [PSI+] prion variants.

The yeast prion [PSI+] is a self-propagating amyloid of the translation termination factor, Sup35p. For known pathogenic prions, such as [PSI+], a single protein can form an array of different amyloid structures (prion variants) each stably inherited and with differing biological properties. The ribosome-associated chaperones, Ssb1/2p (Hsp70s), and RAC (Zuo1p (Hsp40) and Ssz1p (Hsp70)), enhance de novo protein folding by protecting nascent polypeptide chains from misfolding and maintain translational fidelity by involvement in translation termination. Ssb1/2p and RAC chaperones were previously found to inhibit [PSI+] prion generation. We find that most [PSI+] variants arising in the absence of each chaperone were cured by restoring normal levels of that protein. [PSI+] variants hypersensitive to Ssb1/2p have distinguishable biological properties from those hypersensitive to Zuo1p or Ssz1p. The elevated [PSI+] generation frequency in each deletion strain is not due to an altered [PIN+], another prion that primes [PSI+] generation. [PSI+] prion generation/propagation may be inhibited by Ssb1/2/RAC chaperones by ensuring proper folding of nascent Sup35p, thus preventing its joining amyloid fibers. Alternatively, the effect of RAC/Ssb mutations on translation termination and the absence of an effect on the [URE3] prion suggest an effect on the mature Sup35p such that it does not readily join amyloid filaments. Ssz1p is degraded in zuo1Δ [psi-] cells, but not if the cells carry any of several [PSI+] variants. Our results imply that prions arise more frequently than had been thought but the cell has evolved exquisite antiprion systems that rapidly eliminate most variants.

Phase separation by ssDNA binding protein controlled via protein-protein and protein-DNA interactions.

Bacterial single-stranded (ss)DNA-binding proteins (SSB) are essential for the replication and maintenance of the genome. SSBs share a conserved ssDNA-binding domain, a less conserved intrinsically disordered linker (IDL), and a highly conserved C-terminal peptide (CTP) motif that mediates a wide array of protein-protein interactions with DNA-metabolizing proteins. Here we show that the Escherichia coli SSB protein forms liquid-liquid phase-separated condensates in cellular-like conditions through multifaceted interactions involving all structural regions of the protein. SSB, ssDNA, and SSB-interacting molecules are highly concentrated within the condensates, whereas phase separation is overall regulated by the stoichiometry of SSB and ssDNA. Together with recent results on subcellular SSB localization patterns, our results point to a conserved mechanism by which bacterial cells store a pool of SSB and SSB-interacting proteins. Dynamic phase separation enables rapid mobilization of this protein pool to protect exposed ssDNA and repair genomic loci affected by DNA damage.

Time-Dependent Analysis of Sicca Symptoms and Anti-Ro/SSA and Anti-La/SSB Antibodies in Patients with AQP4-IgG-Positive Neuromyelitis Optica Spectrum Disorder.

Anti-aquaporin-4 antibody (AQP4-IgG)-positive neuromyelitis optica spectrum disorder (NMOSD) and Sjögren syndrome (SS) are likely comorbidities. However, the exact effects of age and disease duration on the positivity rates of serum anti-Ro/SSA and anti-La/SSB (anti-SSA/SSB) antibodies and the presence of sicca symptoms in patients with AQP4-IgG remain unknown. In the present study, we evaluated the data from patients with suspected NMOSD who had neurological episodes and tested for serum AQP4-IgG. Associations between the presence of serum AQP4-IgG and SS-related findings were evaluated. The presence of anti-SSA/SSB antibodies [odds ratio (OR), 7.34; 95% confidence interval (CI), 5.71-9.43; p < 0.0001] and that of sicca symptoms (OR, 2.08; 95% CI, 1.67-2.58; p < 0.0001) were both higher in patients with AQP4-IgG (n = 1,651) than in those without AQP4-IgG (n = 2,796). Meanwhile, neither age nor the elapsed time from neurological onset was linked to the prevalence of anti-SSA/SSB antibodies or sicca symptoms, and the prevalence rates of the SS-related factors were elevated since the onset of neurological episodes in those with AQP4-IgG. The frequency of sicca symptoms among those with anti-SSA/SSB antibodies was irrespective of AQP4-IgG (OR, 1.11; 95% CI, 0.67-1.85; p = 0.6892). The measured AQP4-IgG titers did not differ significantly according to the presence of anti-SSA/SSB antibodies (p = 0.2386; Mann-Whitney U test). In summary, age and duration of NMOSD were not the factors producing an elevated prevalence of anti-SSA/SSB antibodies and sicca symptoms in patients with AQP4-IgG, implying that the occurrence of comorbid SS is likely to temporarily precede or synchronize with the onset of AQP4-IgG-positive NMOSD.