Simulation Investigation on the Influence Mechanism of Toluene and Heptane on the Aggregation of Asphaltene Molecules.

Asphaltenes are a group of compounds that are soluble in benzene and toluene but insoluble in nonpolar small molecule n-alkanes. The asphaltene aggregation in the asphaltene-heptane-toluene system was studied using molecular dynamics (MD) simulation, and the interaction between asphaltene molecules during this process was also revealed from the evolution of the density field, radial distribution function (RDF), and intermolecular distance of asphaltenes. Three main findings were made: (1) more asphaltene precipitates (heptane) were contained, and more asphaltene dimers or trimers were formed during the MD simulation; (2) asphaltene molecules interacted with each other to form aggregates in the form of π-π or H-bond interaction. The stable distance of the π-π interaction was 3.3-3.5 Å, and the stable distance of the H-bond connection was 1.7-1.9 Å. (3) The asphaltene interaction in the heptane-rich system was dominated by π-π interaction between asphaltene molecules. However, the asphaltene interactions in the toluene-rich system were mainly the π-π interaction between asphaltene molecules and toluene and the H-bond interaction between the side chains of asphaltene molecules. The results of this study can aid in understanding how asphaltene molecules aggregate and self-associate and can also offer theoretical support for flow assurance in systems used to produce crude oil.

Association of sleep disorders with asthma: a meta-analysis.

BACKGROUND: Animal experiments and clinical trials have revealed a potential relationship between sleep disorders and asthma. However, the associations between these factors remain unclear. MATERIAL AND METHODS: We searched PubMed, Embase, Web of Science and Cochrane Library databases for eligible studies published before 30 December 2022. Studies investigating the association between sleep disorders (insomnia, poor sleep quality and insufficient sleep time) and asthma were selected. Sleep disorders were assessed using questionnaires, interviews, or medical records. Asthma was diagnosed based on medical history and drug use. The Newcastle-Ottawa Scale and the Agency for Healthcare Research and Quality checklist were employed for quality assessment. We used OR with 95% CI as the effect measures and forest plots to display the results. Heterogeneity was evaluated using I2 statistics and subgroup analyses were performed for bias analysis. Publication bias was evaluated using the funnel plots and Egger's test. RESULTS: Twenty-three studies were included in the primary analysis, which suggested a positive association between sleep disorders and asthma (OR: 1.38, 95% CI 1.10 to 1.74). Subgroup analyses were conducted according to the study design, age, family history of asthma and type of sleep disorders. We did not find any association between sleep disorders and asthma in children aged ˂12 years (OR: 1.13, 95% CI 0.97 to 1.32). The association was insignificant in studies where the family history of asthma was adjusted for (OR: 1.16, 95% CI 0.94 to 1.42). Funnel plot and Egger's test indicated a significant publication bias. CONCLUSION: Sleep disorders are associated with an increased prevalence and incidence of asthma. However, the quality of the evidence was low because of potential biases. PROSPERO REGISTRATION NUMBER: CRD42023391989.

Improved Antimicrobial Activity of Bovine Lactoferrin Peptide (LFcinB) Based on Rational Design.

Bovine lactoferrin peptide (LFcinB), as an antimicrobial peptide, is expected to be an alternative of antibiotics owing to its broad-spectrum antimicrobial activity and specific mechanism. However, the weak antimicrobial activity, high hemolysis, and poor stability of LFcinB limited its applications in the field of biomedicine, food and agriculture. In order to improve the antimicrobial activity of LFcinB, five mutants were designed rationally, of which mutant LF4 (M10W/P16R/A24L) showed highest antimicrobial activity. The bioinformatics analysis indicated that the improved antimicrobial activity of LF4 was related to its increased cations, higher amphiphilicity and the extension of the ß-sheet in the structure. These studies will highlight the important role of bioinformatic tools in designing ideal biopeptides and lay a foundation for further development of antimicrobial peptides.

Online calculator for predicting the risk of malignancy in patients with pancreatic cystic neoplasms: A multicenter, retrospective study.

BACKGROUND: Efficient and practical methods for predicting the risk of malignancy in patients with pancreatic cystic neoplasms (PCNs) are lacking. AIM: To establish a nomogram-based online calculator for predicting the risk of malignancy in patients with PCNs. METHODS: In this study, the clinicopathological data of target patients in three medical centers were analyzed. The independent sample t-test, Mann-Whitney U test or chi-squared test were used as appropriate for statistical analysis. After univariable and multivariable logistic regression analysis, five independent factors were screened and incorporated to develop a calculator for predicting the risk of malignancy. Finally, the concordance index (C-index), calibration, area under the curve, decision curve analysis and clinical impact curves were used to evaluate the performance of the calculator. RESULTS: Enhanced mural nodules [odds ratio (OR): 4.314; 95% confidence interval (CI): 1.618-11.503, P = 0.003], tumor diameter ≥ 40 mm (OR: 3.514; 95%CI: 1.138-10.849, P = 0.029), main pancreatic duct dilatation (OR: 3.267; 95%CI: 1.230-8.678, P = 0.018), preoperative neutrophil-to-lymphocyte ratio ≥ 2.288 (OR: 2.702; 95%CI: 1.008-7.244, P = 0.048], and preoperative serum CA19-9 concentration ≥ 34 U/mL (OR: 3.267; 95%CI: 1.274-13.007, P = 0.018) were independent risk factors for a high risk of malignancy in patients with PCNs. In the training cohort, the nomogram achieved a C-index of 0.824 for predicting the risk of malignancy. The predictive ability of the model was then validated in an external cohort (C-index: 0.893). Compared with the risk factors identified in the relevant guidelines, the current model showed better predictive performance and clinical utility. CONCLUSION: The calculator demonstrates optimal predictive performance for identifying the risk of malignancy, potentially yielding a personalized method for patient selection and decision-making in clinical practice.

High extinction ratio and low backreflection polarization maintaining hollow-core to solid-core fiber interconnection.

We develop a hybrid cold/heat two-step splicing approach for low loss, low backreflection, and high polarization extinction ratio (PER) hollow-core to solid-core fiber interconnection. The employed hollow-core fiber (HCF) is our recently developed high-birefringence polarization-maintaining hollow-core fiber (PM-HCF) with a PER value of ∼30 dB, and the solid-core fiber (SCF) is a commercial Panda polarization-maintaining fiber (Panda fiber). Simultaneous low backreflection (<-35 dB), low insertion loss (IL) (∼0.7 dB), and high PER (∼27 dB) are achieved, representing the first high-performance PM-HCF/SCF interconnections, to the best of our knowledge. This greatly facilitates the applications of PM-HCF in widespread fields such as precise metrologies, gyroscopes, and ultrafast/high-power laser deliveries.

Study on Restart Safety of Waxy Crude Pipelines Based on Reliability Principle under Constant Flow.

The restart process of waxy crude pipelines is an unsteady thermo-hydraulic coupling process, which mainly includes two modes of the constant flow and constant pressure in industry. However, some parameters involved in the restart process have obvious uncertainties, such as the operating parameters, physical parameters of crude oil, environmental parameters, and pipeline parameters, resulting in the traditional deterministic method that cannot scientifically describe the safety of the pipeline restart process. To do this, this study introduces the reliability-based limit state method and interference principle into the safety evaluation of waxy crude pipelines during the restart process. Considering the random fluctuation characteristics of the mentioned parameters, the restart physical process, the flow and heat transfer mathematical model, and the restart failure limit state function were established. On this basis, the failure probability during the restart process for one waxy crude pipeline under constant flow was determined. This research has realized the quantitative evaluation of restart safety of waxy crude pipelines.

Improving Superconducting Performance of Fe(Se, Te) with In Situ Formed Grain-Boundary Strengthening and Flux Pinning Centers.

It is well known that the existence of interstitial Fe is a great obstacle to enhancing the superconducting properties of the Fe(Se, Te) system. In this work, a silver and oxygen codoping effect toward enhancement of the superconductivity and flux pinning in Fe(Se, Te) bulks is reported. The oxygen ions from SeO2 can induce the precipitation of interstitial Fe as Fe2O3, thus simultaneously optimizing the superconducting properties of Fe(Se, Te) and forming extra flux pinning centers, while the existence of Ag can enhance the intergrain connections of the polycrystalline material by improving the electron transport at grain boundaries. Compared with the undoped sample, the critical current density, the upper critical field, and the thermally activated flux flow activation energy are greatly enhanced by 4.7, 1.7, and 1.5 times, respectively. The novel synthesis technique and optimized properties of this work can pave the way for the development of high-performance Fe(Se, Te) superconducting wires or tapes.

Prevalence of musculoskeletal discomfort among female cabin crew in Taiwan.

OBJECTIVES: This study investigated the prevalence of musculoskeletal discomfort among female cabin crew through cabin tasks and demographic factors, including age and seniority. METHODS: This study conducted an online questionnaire survey targeted at female cabin crew in Taiwan and ensured that the sample size was with a statistical power of 0.95. This study evaluated the work intensity by ranking six common cabin tasks and examined musculoskeletal discomfort with Cornell Musculoskeletal Discomfort Questionnaire. Descriptive statistics were used to learn the work intensity and discomfort conditions. In addition, the Chi-square test of independence and multivariate adjustment were applied to clarify the impact of age and occupation on musculoskeletal discomfort in the neck, shoulders, and lower back. RESULTS: This study enrolled 88 female cabin crew members. Handling carry-on baggage was voted as the highest intensity cabin task (40%), which was also ranked as the strongest intensity on shoulders. Meanwhile, the upper trunk was more prevalent in musculoskeletal discomfort. Moreover, after multivariate adjustment with controlling the effect of age, this study found a marginal significant association (p = .09) between seniority and right shoulder discomfort for younger staff. CONCLUSION: This study found that handling carry-on baggage was associated with musculoskeletal complaints in the shoulders. Therefore, this study suggested that shoulders, especially for the right side might be related to the occupational injury, which was prevalent along with seniority among the younger crew. Overall, this study provided the preliminary findings to improve occupational training for preventive health.

Acute and life-threatening complications in patients with anorexia nervosa: A case report and literature study.

Anorexia nervosa (AN) is characterized by a strong fear of weight gain and body image disorders and is classified as a mental illness that can cause direct damage to one's mental health and body. Many individuals with AN tend to commit suicide. Additionally, the disease can lead to chronic undernutrition and low body weight, adversely affecting each body system, exacerbating systemic medical complications, especially acute life-threatening complications. Therefore, AN has the highest mortality and disability rates among all mental diseases. There is a basic clinical need to identify and address the acute and critical complications of this disease as soon as possible. However, the current literature has a poor description of the acute and critical complications of AN and lacks a systematic review. We report a case of a patient with AN and severe hypokalemia, significant Q-T interval prolongation, stomach dilation, and intestinal obstruction who recovered after conservative treatment. The defecation method we used, to our knowledge, has not been previously reported in the literature. We also briefly review the various acute and life-threatening complications of AN.

An Integral Recognition and Signaling for Electrochemical Assay of Protein Kinase Activity and Inhibitor by Reduced Graphene Oxide-Polydopamine-Silver Nanoparticle-Ti4+ Nanocomposite.

A novel electrochemical biosensing method for protein kinase (PKA) activity was demonstrated by using a reduced graphene oxide-polydopamine-silver nanoparticle-Ti4+ (rGO-PDA-AgNPs-Ti4+) nanocomposite. The obtained nanocomposite possessed an integral capability for phosphopeptide recognition and signal readout. The polydopamine modified reduced graphene oxide (rGO-PDA) was firstly prepared based on a self-polymerization method of dopamine. The silver ions were adsorbed onto polydopamine (PDA) layer and directly reduced into silver nanoparticles (AgNPs), which was used for electrochemical signal reporting. Then, the Ti4+ cations were attached onto the PDA layer for phosphopeptide recognition according to the strong coordination ability of PDA with Ti4+ and phosphate group. The prepared rGO-PDA-AgNPs-Ti4+ nanocomposites were characterized with different methods. The developed rGO-PDA-AgNPs-Ti4+ nanocomposites were then employed for electrochemical analysis of PKA-catalyzed kemptide phosphorylation. The sensitive detection toward PKA activity was realized with an experimental detection limit of about 0.01 U/mL. It may be also extended for the inhibitor evaluation. Thus, it provided a facile and sensitive means for electrochemical analysis of PKA activity and inhibitor screening.

General and passenger-relevant factors of work-related musculoskeletal disorders (WMSDs) among Chinese female flight attendants.

BACKGROUND: A high prevalence of work-related musculoskeletal disorders (WMSDs) has been reported among flight attendants. Identifying the root causes of these disorders may improve the health conditions of flight attendants and further improve flight safety and service quality. OBJECTIVE: In this study, we aimed to identify WMSD risk factors for a specific population, namely Chinese female flight attendants. METHODS: A two-stage survey including an online questionnaire (46 flight attendants) and a semi-structured interview (16 flight attendants) was used to assess the WMSDs of Chinese female flight attendants. Text analysis tools in NVivo 11 were used to identify the main concerns and risk factors for WMSDs of Chinese flight attendants. RESULTS: In the online questionnaire, more than 86% of the participants reported discomfort in at least one body part. Biomechanical factors, work organizational factors, and psychosocial factors were reported by participants in this study. Chinese passengers were found to have an effect on WMSD development in Chinese flight attendants. CONCLUSIONS: The results of this study suggested that WMSDs are severe problems among Chinese flight attendants. General factors as well as the passenger-relevant factor were identified as the most influential causes of WMSDs.

Ultrasensitive Electrochemical DNA Biosensor Fabrication by Coupling an Integral Multifunctional Zirconia-Reduced Graphene Oxide-Thionine Nanocomposite and Exonuclease I-Assisted Cleavage.

In this work, a simple but sensitive electrochemical DNA biosensor for nucleic acid detection was developed by taking advantage of exonuclease (Exo) I-assisted cleavage for background reduction and zirconia-reduced graphene oxide-thionine (ZrO2-rGO-Thi) nanocomposite for integral DNA recognition, signal amplification, and reporting. The ZrO2-rGO nanocomposite was obtained by a one-step hydrothermal synthesis method. Then, thionine was adsorbed onto the rGO surface, via π-π stacking, as an excellent electrochemical probe. The biosensor fabrication is very simple, with probe DNA immobilization and hybridization recognition with the target nucleic acid. Then, the ZrO2-rGO-Thi nanocomposite was captured onto an electrode via the multicoordinative interaction of ZrO2 with the phosphate group on the DNA skeleton. The adsorbed abundant thionine molecules onto the ZrO2-rGO nanocomposite facilitated an amplified electrochemical response related with the target DNA. Since upon the interaction of the ZrO2-rGO-Thi nanocomposite with the probe DNA an immobilized electrode may also occur, an Exo I-assisted cleavage was combined to remove the unhybridized probe DNA for background reduction. With the current proposed strategy, the target DNA related with P53 gene could be sensitively assayed, with a wide linear detection range from 100 fM to 10 nM and an attractive low detection limit of 24 fM. Also, the developed DNA biosensor could differentiate the mismatched targets from complementary target DNA. Therefore, it offers a simple but effective biosensor fabrication strategy and is anticipated to show potential for applications in bioanalysis and medical diagnosis.

Development and Preliminary Usability Evaluation of a Somatosensory Square Dance System for Older Chinese Persons: Mixed Methods Study.

BACKGROUND: Chinese square dancing, known as guangchang wu in Chinese, is a well-known public fitness activity that provides an entertaining way for older Chinese women to improve their flexibility, lower extremity strength, overall coordination, and balance. However, injuries, noise conflicts, and lack of space are challenging aspects of this activity. Somatosensory games (SG) are an increasingly popular physical fitness approach to enhance the selective attention of older persons with indoor engagement and exercises. OBJECTIVE: The objectives of this study were to develop a newly designed somatosensory square dance system for older Chinese people and to evaluate its usability. METHODS: This is a mixed methods study. The newly designed somatosensory square dance system is a somatic training tool that provides adequate Chinese square dance fitness training based on Laban Movement Analysis (LMA) and design guidelines established in a previous stage. The usability evaluation involved a questionnaire and interviews. Twelve participants were interviewed before and after experiencing the 15-minute dancing and learning process within the program. In addition, participants scored their experience satisfaction in psychological, physiological, and relaxation sections on a scale of 1 to 5 using a questionnaire. Qualitative content analysis and quantitative analysis of the satisfaction scores supported understanding of usability problems. RESULTS: Based on the interview results, 6/12 (50%) of the participants thought the system could help them correct their dancing movements indoors without being affected by poor outdoor weather. Among the participants, 3/12 (25%) indicated that this indoor system could enable them to enjoy fitness activities in a private space. Moreover, 3/12 participants (25%) stated that this system could promote family relationships by providing easy dancing movements. All participants were highly satisfied with the relaxation aspect of the system (4.45/5). The participants were all psychologically satisfied and interested in the novel features of the system, with an average score of 4.16/5. Physiologically, participants affirmed that the system could help them maintain good health (4.91/5). CONCLUSIONS: The results of this study suggest that the somatosensory square dance system can be used as an indoor fitness tool to improve older Chinese square dancers' health conditions with reasonable dance training. Noise and space conflicts can be addressed. The Laban Elated Square Dance system, which was modified by therapists based on LMA and square dance design guidelines, was highly approved by dancers because it decreased the possibility of injuries, falls, and joint damage by considering the physical and psychological difficulties of older persons. Different features will be considered in the next stage, such as greater selection of exercises and difficulty level settings. Users' social needs will also be explored in subsequent stages.

Study on demulsification and deoiling for O/W emulsion by microbubble pretreated resin.

The microbubble pretreated resin was used for demulsification and deoiling of the simulated O/W emulsion. The demulsification and deoiling performance and the influencing factors were investigated systematically. Experimental results indicate that the microbubble pretreated resin reaches a 97% oil removal within 80 min; on the contrary, oil removals are 90% and 85% for NaOH solution soaked and un-pretreated resins respectively. After five repeated runs, the oil removal of microbubble pretreated resin can be maintained at over 70%. The demulsification mechanism was revealed by comparing zeta potential, surface tension, contact angle of the emulsion in treatment, and the characterization results of the resin before and after use. Three possible pathways of demulsification were concluded and the ranking contributions can be shown below. Pathway 1: Competitive trapping of surfactant. The cationic groups of the resin combine with the anionic groups of the surfactant and drag them away from the oil particle surface. Pathway 2: Distribution equilibrium of surfactant. Free surfactants in the emulsion are captured by resin and reduce the concentration of uncombined surfactant. This results in surfactants on the oil particle partly detaching from the oil surface to maintain the adsorption-desorption equilibrium of the surfactant. Pathway 3: Adsorption coalescence.

Preparation of magnetic hydrogel microspheres of lignin derivate for application in water.

A low-cost and well-separated approach is introduced for adsorption pollutants in water. Chemical modified lignin is prepared with diethylenetriamine to enhance the reaction activities, then used to prepare lignin derivate magnetic hydrogel microspheres (LDMHMs) via blending with Fe3O4. The LDMHMs are successful prepared by the determination of FT-IR data, and the morphology shown from SEM imagine indicates the LDMHMs are in nanosized. The prepared LDMHMs are used as adsorbents for organic dyes, such as methylene blue (MB), methyl orange (MO) and malachite green (MG), the plateaus data are 43 mg/g, 39 mg/g and 155 mg/g, respectively. For inorganic pollutions, such as Pb2+, Hg2+ and Ni2+, the plateaus data are 33 mg/g, 55 mg/g and 23 mg/g, respectively. The adsorption data of unmodified lignin are 2.6 mg/g (Pb2+), 3.3 mg/g (Hg2+), 2.1 mg/g (Ni2+), 8 mg/g (MB), 10 mg/g (MG) and 2 mg/g (MO) in the same condition. The adsorbents are recycled by magnetic separation, regenerating from acid condition and reused for multiple cycles. The regeneration ratios are all above 90%, indicating a highly reusability and further reducing the cost of the treatment.

Super-swelling lignin-based biopolymer hydrogels for soil water retention from paper industry waste.

Sources of pulping red liquor, which is produced by acidic sulfite cooking in paper industry, consisted of lignosulphonate and polysaccharide, commonly considered as waste or byproducts and used in low value, such as surfactant and adhesive are wide and its price is low. Here a novel method for high value-added utilization of the pulp and paper industry waste for fabricating super-swelling biopolymer hydrogels is introduced. In contrast to other costly utilizations, which are needed to separate red liquor or purify hemicellulose and lignin before using, it is first time to directly utilize red liquor to prepare hydrogels without pretreatment. FT-IR, SEM, TGA and XRD are used to determine structure and morphology of hydrogels. It is excited the hydrogels fabricated from acrylic (AA) and industry waste exhibit super-swelling and slow release behaviors in water. Compared with synthetic materials, the hydrogels are at low price to be chosen as candidates for water retention agent for agriculture.

The Influence of Self-Efficacy and Work Input on Physical Education Teachers' Creative Teaching.

OBJECTIVES: To explore the influence of different background factors on middle school PE teachers' self-efficacy, work input and creative teaching, and to reveal the relationship between teaching self-efficacy and work input on creative teaching. METHODS: By means of self-efficacy, work engagement and creative teaching scale, a questionnaire survey was conducted among middle school PE teachers, and the data were processed and modeled by SPSS and AMOS statistical analysis software. RESULTS: Physical education (PE) teachers' self-teaching effectiveness was influenced by background factors such as gender, age, teaching age, full-time or part-time work and educational level. Work input was only affected by age, teaching experience and educational level, while creative teaching seemed to be only related to background factors such as educational background and full-time or part-time work; PE teachers' general teaching effectiveness and personal teaching effectiveness had significant positive effects on energy input, concentration input, dedication input, cognitive creativity, skill creativity and emotional creativity; Concentration input had a significant positive impact on the three-dimensional of creative teaching, while energy input and dedication input had no impact on the three-dimensional of creative teaching; Work input as an intermediary variable of self-efficacy's influence on creative teaching had been verified, but the real intermediary role was not the whole work input, but the concentration input in its structure. CONCLUSION: Both general and individual teaching effectiveness had positive effects on work input and creative teaching, but the energetic and dedicated input in work input cannot promote teachers' creative teaching effectively. Therefore, the professional ethics training of PE teachers in their enthusiasm and dedication to work should be strengthened.

Insights into Substrate Specificity of NlpC/P60 Cell Wall Hydrolases Containing Bacterial SH3 Domains.

UNLABELLED: Bacterial SH3 (SH3b) domains are commonly fused with papain-like Nlp/P60 cell wall hydrolase domains. To understand how the modular architecture of SH3b and NlpC/P60 affects the activity of the catalytic domain, three putative NlpC/P60 cell wall hydrolases were biochemically and structurally characterized. These enzymes all have γ-d-Glu-A2pm (A2pm is diaminopimelic acid) cysteine amidase (or dl-endopeptidase) activities but with different substrate specificities. One enzyme is a cell wall lysin that cleaves peptidoglycan (PG), while the other two are cell wall recycling enzymes that only cleave stem peptides with an N-terminal l-Ala. Their crystal structures revealed a highly conserved structure consisting of two SH3b domains and a C-terminal NlpC/P60 catalytic domain, despite very low sequence identity. Interestingly, loops from the first SH3b domain dock into the ends of the active site groove of the catalytic domain, remodel the substrate binding site, and modulate substrate specificity. Two amino acid differences at the domain interface alter the substrate binding specificity in favor of stem peptides in recycling enzymes, whereas the SH3b domain may extend the peptidoglycan binding surface in the cell wall lysins. Remarkably, the cell wall lysin can be converted into a recycling enzyme with a single mutation. IMPORTANCE: Peptidoglycan is a meshlike polymer that envelops the bacterial plasma membrane and bestows structural integrity. Cell wall lysins and recycling enzymes are part of a set of lytic enzymes that target covalent bonds connecting the amino acid and amino sugar building blocks of the PG network. These hydrolases are involved in processes such as cell growth and division, autolysis, invasion, and PG turnover and recycling. To avoid cleavage of unintended substrates, these enzymes have very selective substrate specificities. Our biochemical and structural analysis of three modular NlpC/P60 hydrolases, one lysin, and two recycling enzymes, show that they may have evolved from a common molecular architecture, where the substrate preference is modulated by local changes. These results also suggest that new pathways for recycling PG turnover products, such as tracheal cytotoxin, may have evolved in bacteria in the human gut microbiome that involve NlpC/P60 cell wall hydrolases.

Unique requirements for mono- and polyubiquitination of the peroxisomal targeting signal co-receptor, Pex20.

In Pichia pastoris, the peroxisomal targeting signal 2 (PTS2)-dependent peroxisomal matrix protein import pathway requires the receptor, Pex7, and its co-receptor Pex20. A conserved lysine (Lys(19)) near the N terminus of Pex20 is required for its polyubiquitination and proteasomal degradation, whereas a conserved cysteine (Cys(8)) is essential for its recycling. In this study, we found that Cys(8) is required for the DTT-sensitive mono- and diubiquitination of Pex20. We also show that the PTS2 cargo receptor, Pex7, is required for Pex20 polyubiquitination. Pex4, the E2 ubiquitin-conjugation enzyme, is required for monoubiquitination of Pex20. However, it is also necessary for polyubiquitination of Pex20, making its behavior distinct from the ubiquitination described for other PTS receptors. Unlike the roles of specific RING peroxins in Pex5 ubiquitination, we found that all the RING peroxins (Pex2, Pex10, and Pex12) are required as E3 ubiquitin ligases for Pex20 mono- and polyubiquitination. A model for Pex20 ubiquitination is proposed based on these observations. This is the first description of the complete ubiquitination pathway of Pex20, which provides a better understanding of the recycling and degradation of this PTS2 cargo co-receptor.

Recent advances in peroxisomal matrix protein import.

Peroxisomes are essential organelles responsible for many metabolic reactions, such as the oxidation of very long chain and branched fatty acids, D-amino acids and polyamines, as well as the production and turnover of hydrogen peroxide. They comprise a class of organelles called microbodies, including glycosomes, glyoxysomes and Woronin bodies. Dysfunction of human peroxisomes causes severe and often fatal peroxisome biogenesis disorders (PBDs). Peroxisomal matrix protein import is mediated by receptors that shuttle between the cytosol and peroxisomal matrix using ubiquitination/deubiquitination reactions and ATP hydrolysis for receptor recycling. We focus on the machinery involved in the peroxisomal matrix protein import cycle, highlighting recent advances in peroxisomal matrix protein import, cargo release and receptor recycling/degradation.