A Review: Molecular Chaperone-mediated Folding, Unfolding and Disaggregation of Expressed Recombinant Proteins

Soluble expression of hMYDGF was improved by strain engineering and optimizations of fermentation strategies in Escherichia coli

Myeloid-derived growth factor (MYDGF) is a cytokine that exhibits a variety of biological functions. This study focused on utilizing BL21(DE3) strain engineering and fermentation strategies to achieve high-level expression of soluble human MYDGF (hMYDGF) in Escherichia coli. Initially, the E. coli expressing strain BL21(DE3) was engineered by deleting the IpxM gene and inserting the GROEL/S and Trigger factor genes. The engineered E. coli strain BL21(TG)/pT-MYDGF accumulated 3557.3 ± 185.6 μg/g and 45.7 ± 6.7 mg/L of soluble hMYDGF in shake flask fermentation, representing a 15.6-fold increase compared to the control strain BL21(DE3)/pT-MYDGF. Furthermore, the yield of hMYDGF was significantly enhanced by optimizing the fermentation conditions. Under optimized conditions, the 5L bioreactor yielded up to 2665.8 ± 164.3 μg/g and 407.6 ± 42.9 mg/L of soluble hMYDGF. The results indicate that the implementation of these optimization strategies could enhance the ratio and yield of soluble proteins expressed by E.coli, thereby meeting the demands of industrial production. This study employed sophisticated strategies to lay a solid foundation for the industrial application of hMYDGF.

Research progress on the functions and biosynthesis of theaflavins

Theaflavins are beneficial to human health due to various bioactivities. Biosynthesis of theaflavins using polyphenol oxidase (PPO) is advantageous due to cost effectiveness and environmental friendliness. In this review, studies on the mechanism of theaflavins formation, the procedures to screen and prepare PPOs, optimization of reaction systems and immobilization of PPOs were described. The challenges associated with the mass biosynthesis of theaflavins, such as poor enzyme activity, undesirable subproducts and inclusion bodies of recombinant PPOs were presented. Further strategies to solve these challenges and improve theaflavins production, including enzyme engineering, immobilization enzyme technology, water-immiscible solvent-water biphasic systems and recombinant enzyme technology, were proposed.

Comprehensive Overview of Bottom-Up Proteomics Using Mass Spectrometry

Proteomics is the large scale study of protein structure and function from biological systems through protein identification and quantification. "Shotgun proteomics" or "bottom-up proteomics" is the prevailing strategy, in which proteins are hydrolyzed into peptides that are analyzed by mass spectrometry. Proteomics studies can be applied to diverse studies ranging from simple protein identification to studies of proteoforms, protein-protein interactions, protein structural alterations, absolute and relative protein quantification, post-translational modifications, and protein stability. To enable this range of different experiments, there are diverse strategies for proteome analysis. The nuances of how proteomic workflows differ may be challenging to understand for new practitioners. Here, we provide a comprehensive overview of different proteomics methods. We cover from biochemistry basics and protein extraction to biological interpretation and orthogonal validation. We expect this Review will serve as a handbook for researchers who are new to the field of bottom-up proteomics.

Evaluating the ability of different chaperones in improving soluble expression of a triple-mutated human interferon gamma in Escherichia coli

Human interferon gamma (hIFN-γ) plays a pivotal role as a soluble cytokine with diverse functions in both innate and adaptive immunity. In a previous investigation, we pinpointed three critical amino acid residues, i.e., threonine (T) 27, phenylalanine (F) 29, and leucine (L) 30, on the IFN-γ structure, which are integral to the epitope recognized by anti-IFN-γ autoantibodies. It is crucial to impede the interaction between this epitope and autoantibodies for effective therapy in adult-onset immunodeficiency (AOID). However, the challenge arises from the diminished solubility of the T27AF29L30A mutant in Escherichia coli BL21(DE3). This study delves into a targeted strategy aimed at improving the soluble expression of IFN-γ T27AF29AL30A. This is achieved through the utilization of five chaperone plasmids: pG-KJE8, pKJE7, pGro7, pG-Tf2, and pTf16. These plasmids, encoding cytoplasmic chaperones, are co-expressed with the IFN-γ mutant in E. coli BL21(DE3), and we meticulously analyze the proteins in cell lysate and inclusion bodies using SDS-PAGE and Western blotting. Our findings reveal the remarkable efficacy of pG-KJE8, which houses cytoplasmic chaperones DnaK-DnaJ-GrpE and GroEL-GroES, in significantly enhancing the solubility of IFN-γ T27AF29AL30A. Importantly, this co-expression not only addresses solubility concerns but also preserves the functional dimerized structure, as confirmed by sandwich ELISA. This promising outcome signifies a significant step forward in developing biologic strategies for AOID.

Powdery mildew effectors AVRA1 and BEC1016 target the ER J-domain protein HvERdj3B required for immunity in barley

The barley powdery mildew fungus, Blumeria hordei (Bh), secretes hundreds of candidate secreted effector proteins (CSEPs) to facilitate pathogen infection and colonization. One of these, CSEP0008, is directly recognized by the barley nucleotide-binding leucine-rich-repeat (NLR) receptor MLA1 and therefore is designated AVRA1. Here, we show that AVRA1 and the sequence-unrelated Bh effector BEC1016 (CSEP0491) suppress immunity in barley. We used yeast two-hybrid next-generation interaction screens (Y2H-NGIS), followed by binary Y2H and in planta protein-protein interactions studies, and identified a common barley target of AVRA1 and BEC1016, the endoplasmic reticulum (ER)-localized J-domain protein HvERdj3B. Silencing of this ER quality control (ERQC) protein increased Bh penetration. HvERdj3B is ER luminal, and we showed using split GFP that AVRA1 and BEC1016 translocate into the ER signal peptide-independently. Overexpression of the two effectors impeded trafficking of a vacuolar marker through the ER; silencing of HvERdj3B also exhibited this same cellular phenotype, coinciding with the effectors targeting this ERQC component. Together, these results suggest that the barley innate immunity, preventing Bh entry into epidermal cells, requires ERQC. Here, the J-domain protein HvERdj3B appears to be essential and can be regulated by AVRA1 and BEC1016. Plant disease resistance often occurs upon direct or indirect recognition of pathogen effectors by host NLR receptors. Previous work has shown that AVRA1 is directly recognized in the cytosol by the immune receptor MLA1. We speculate that the AVRA1 J-domain target being inside the ER, where it is inapproachable by NLRs, has forced the plant to evolve this challenging direct recognition.

Exploiting cyclodextrins as artificial chaperones to enhance enzyme protection through supramolecular engineering

We report a method of enzyme stabilisation exploiting the artificial protein chaperone properties of β-cyclodextrin (β-CD) covalently embedded in an ultrathin organosilica layer. Putative interaction points of this artificial chaperone system with the surface of the selected enzyme were studied in silico using a protein energy landscape exploration simulation algorithm. We show that this enzyme shielding method allows for drastic enhancement of enzyme stability under thermal and chemical stress conditions, along with broadening the optimal temperature range of the biocatalyst. The presence of the β-CD macrocycle within the protective layer supports protein refolding after treatment with a surfactant.

Enhanced expression of a novel trypsin from Streptomyces fradiae in Komagataella phaffii GS115 through combinational strategies of propeptide engineering and self-degredation sites modification

This study aimed to enhance the expression level of a novel trypsin gene from Streptomyces fradiae ATCC14544 in Komagataella phaffii GS115 through the combinational use of propeptide engineering and self-degradation residues modification strategies. An artificial propeptide consisted of thioredoxin TrxA, the bovine propeptide DDDDK and the hydrophobic peptide FVEF was introduced to replace the original propeptide while the self-degradation residue sites were predicted and analyzed through alanine screening. The results showed that the quantity and enzymatic activity of asft with engineered propeptide reached 47.02 mg/mL and 33.9 U/mL, which were 9.6 % and 59.29 % higher than those of wild-type (42.9 mg/mL and 13.8 U/mL). Moreover, the introduction of R295A/R315A mutation further enhanced the enzymatic activity (58.86 U/mL) and obviously alleviated the phenomena of self-degradation. The tolerance of trypsin towards alkaline environment was also improved since the optimal pH was shifted from pH 9.0 to pH 9.5 and the half-life value at pH 10 was significantly extended. Finally, the fermentation media composition and condition were optimized and trypsin activity in optimal condition reached 160.58 U/mL, which was 2.73-fold and 11.64-fold of that before optimization or before engineering. The results obtained in this study indicated that the combinational use of propeptide engineering and self-degradation sites modification might have great potential application in production of active trypsins.

Stabilization challenges and aggregation in protein-based therapeutics in the pharmaceutical industry

Protein-based therapeutics have revolutionized the pharmaceutical industry and become vital components in the development of future therapeutics. They offer several advantages over traditional small molecule drugs, including high affinity, potency and specificity, while demonstrating low toxicity and minimal adverse effects. However, the development and manufacturing processes of protein-based therapeutics presents challenges related to protein folding, purification, stability and immunogenicity that should be addressed. These proteins, like other biological molecules, are prone to chemical and physical instabilities. The stability of protein-based drugs throughout the entire manufacturing, storage and delivery process is essential. The occurrence of structural instability resulting from misfolding, unfolding, and modifications, as well as aggregation, poses a significant risk to the efficacy of these drugs, overshadowing their promising attributes. Gaining insight into structural alterations caused by aggregation and their impact on immunogenicity is vital for the advancement and refinement of protein therapeutics. Hence, in this review, we have discussed some features of protein aggregation during production, formulation and storage as well as stabilization strategies in protein engineering and computational methods to prevent aggregation.

Engineering and Expression Strategies for Optimization of L-Asparaginase Development and Production

Genetic engineering for heterologous expression has advanced in recent years. Model systems such as Escherichia coli, Bacillus subtilis and Pichia pastoris are often used as host microorganisms for the enzymatic production of L-asparaginase, an enzyme widely used in the clinic for the treatment of leukemia and in bakeries for the reduction of acrylamide. Newly developed recombinant L-asparaginase (L-ASNase) may have a low affinity for asparagine, reduced catalytic activity, low stability, and increased glutaminase activity or immunogenicity. Some successful commercial preparations of L-ASNase are now available. Therefore, obtaining novel L-ASNases with improved properties suitable for food or clinical applications remains a challenge. The combination of rational design and/or directed evolution and heterologous expression has been used to create enzymes with desired characteristics. Computer design, combined with other methods, could make it possible to generate mutant libraries of novel L-ASNases without costly and time-consuming efforts. In this review, we summarize the strategies and approaches for obtaining and developing L-ASNase with improved properties.

Hydroxylases involved in terpenoid biosynthesis: a review

Terpenoids are pervasive in nature and display an immense structural diversity. As the largest category of plant secondary metabolites, terpenoids have important socioeconomic value in the fields of pharmaceuticals, spices, and food manufacturing. The biosynthesis of terpenoid skeletons has made great progress, but the subsequent modifications of the terpenoid framework are poorly understood, especially for the functionalization of inert carbon skeleton usually catalyzed by hydroxylases. Hydroxylase is a class of enzymes that plays an important role in the modification of terpenoid backbone. This review article outlines the research progress in the identification, molecular modification, and functional expression of this class of enzymes in the past decade, which are profitable for the discovery, engineering, and application of more hydroxylases involved in the plant secondary metabolism.

Critical Beginnings: Selective Tuning of Solubility and Structural Accuracy of Newly Synthesized Proteins by the Hsp70 Chaperone System

Proteins are particularly prone to aggregation immediately after release from the ribosome, and it is therefore important to elucidate the role of chaperones during these key steps of protein life. The Hsp70 and trigger factor (TF) chaperone systems interact with nascent proteins during biogenesis and immediately post-translationally. It is unclear, however, whether these chaperones can prevent formation of soluble and insoluble aggregates. Here, we address this question by monitoring the solubility and structural accuracy of globin proteins biosynthesized in an Escherichia coli cell-free system containing different concentrations of the bacterial Hsp70 and TF chaperones. We find that Hsp70 concentrations required to grant solubility to newly synthesized proteins are extremely sensitive to client-protein sequence. Importantly, Hsp70 concentrations yielding soluble client proteins are insufficient to prevent formation of soluble aggregates. In fact, for some aggregation-prone protein variants, avoidance of soluble-aggregate formation demands Hsp70 concentrations that exceed cellular levels in E. coli. In all, our data highlight the prominent role of soluble aggregates upon nascent-protein release from the ribosome and show the limitations of the Hsp70 chaperone system in the case of highly aggregation-prone proteins. These results demonstrate the need to devise better strategies to prevent soluble-aggregate formation upon release from the ribosome.

Distribution and solvent exposure of Hsp70 chaperone binding sites across the Escherichia coli proteome

Many proteins must interact with molecular chaperones to achieve their native state in the cell. Yet, how chaperone binding-site characteristics affect the folding process is poorly understood. The ubiquitous Hsp70 chaperone system prevents client-protein aggregation by holding unfolded conformations and by unfolding misfolded states. Hsp70 binding sites of client proteins comprise a nonpolar core surrounded by positively charged residues. However, a detailed analysis of Hsp70 binding sites on a proteome-wide scale is still lacking. Further, it is not known whether proteins undergo some degree of folding while chaperone bound. Here, we begin to address the above questions by identifying Hsp70 binding sites in 2258 Escherichia coli (E. coli) proteins. We find that most proteins bear at least one Hsp70 binding site and that the number of Hsp70 binding sites is directly proportional to protein size. Aggregation propensity upon release from the ribosome correlates with number of Hsp70 binding sites only in the case of large proteins. Interestingly, Hsp70 binding sites are more solvent-exposed than other nonpolar sites, in protein native states. Our findings show that the majority of E. coli proteins are systematically enabled to interact with Hsp70 even if this interaction only takes place during a fraction of the protein lifetime. In addition, our data suggest that some conformational sampling may take place within Hsp70-bound states, due to the solvent exposure of some chaperone binding sites in native proteins. In all, we propose that Hsp70-chaperone-binding traits have evolved to favor Hsp70-assisted protein folding devoid of aggregation.

Inclusion Bodies: Status Quo and Perspectives

Multiple E. coli cultivations, producing recombinant proteins, lead to the formation of inclusion bodies (IBs). IBs historically were considered as nondesired by-products, due to their time- and cost-intensive purification. Nowadays, many obstacles in IB processing can be overcome. As a consequence, several industrial processes with E. coli favor IB formation over soluble production options due to the high space time yields obtained. Within this chapter, we discuss the state-of-the art biopharmaceutical IB process, review its challenges, highlight the recent developments and perspectives, and also propose alternative solutions, compared to the state-of-the art processing.

Bioprocessing of recombinant proteins from Escherichia coli inclusion bodies: insights from structure-function relationship for novel applications

The formation of inclusion bodies (IBs) during expression of recombinant therapeutic proteins using E. coli is a significant hurdle in producing high-quality, safe, and efficacious medicines. The improved understanding of the structure-function relationship of the IBs has resulted in the development of novel biotechnologies that have streamlined the isolation, solubilization, refolding, and purification of the active functional proteins from the bacterial IBs. Together, this overall effort promises to radically improve the scope of experimental biology of therapeutic protein production and expand new prospects in IBs usage. Notably, the IBs are increasingly used for applications in more pristine areas such as drug delivery and material sciences. In this review, we intend to provide a comprehensive picture of the bio-processing of bacterial IBs, including assessing critical gaps that still need to be addressed and potential solutions to overcome them. We expect this review to be a useful resource for those working in the area of protein refolding and therapeutic protein production.

Synthesis of an Anti-CD7 Recombinant Immunotoxin Based on PE24 in CHO and E. coli Cell-Free Systems

Recombinant immunotoxins (RITs) are an effective class of agents for targeted therapy in cancer treatment. In this article, we demonstrate the straight-forward production and testing of an anti-CD7 RIT based on PE24 in a prokaryotic and a eukaryotic cell-free system. The prokaryotic cell-free system was derived from Escherichia coli BL21 StarTM (DE3) cells transformed with a plasmid encoding the chaperones groEL/groES. The eukaryotic cell-free system was prepared from Chinese hamster ovary (CHO) cells that leave intact endoplasmic reticulum-derived microsomes in the cell-free reaction mix from which the RIT was extracted. The investigated RIT was built by fusing an anti-CD7 single-chain variable fragment (scFv) with the toxin domain PE24, a shortened variant of Pseudomonas Exotoxin A. The RIT was produced in both cell-free systems and tested for antigen binding against CD7 and cell killing on CD7-positive Jurkat, HSB-2, and ALL-SIL cells. CD7-positive cells were effectively killed by the anti-CD7 scFv-PE24 RIT with an IC50 value of 15 pM to 40 pM for CHO and 42 pM to 156 pM for E. coli cell-free-produced RIT. CD7-negative Raji cells were unaffected by the RIT. Toxin and antibody domain alone did not show cytotoxic effects on either CD7-positive or CD7-negative cells. To our knowledge, this report describes the production of an active RIT in E. coli and CHO cell-free systems for the first time. We provide the proof-of-concept that cell-free protein synthesis allows for on-demand testing of antibody−toxin conjugate activity in a time-efficient workflow without cell lysis or purification required.

Systematic bio-fabrication of aptamers and their applications in engineering biology

Aptamers are single-stranded DNA or RNA molecules that have high affinity and selectivity to bind to specific targets. Compared to antibodies, aptamers are easy to in vitro synthesize with low cost, and exhibit excellent thermal stability and programmability. With these features, aptamers have been widely used in biology and medicine-related fields. In the meantime, a variety of systematic evolution of ligands by exponential enrichment (SELEX) technologies have been developed to screen aptamers for various targets. According to the characteristics of targets, customizing appropriate SELEX technology and post-SELEX optimization helps to obtain ideal aptamers with high affinity and specificity. In this review, we first summarize the latest research on the systematic bio-fabrication of aptamers, including various SELEX technologies, post-SELEX optimization, and aptamer modification technology. These procedures not only help to gain the aptamer sequences but also provide insights into the relationship between structure and function of the aptamers. The latter provides a new perspective for the systems bio-fabrication of aptamers. Furthermore, on this basis, we review the applications of aptamers, particularly in the fields of engineering biology, including industrial biotechnology, medical and health engineering, and environmental and food safety monitoring. And the encountered challenges and prospects are discussed, providing an outlook for the future development of aptamers.

Engineering sigma factors and chaperones for enhanced heterologous lipoxygenase production in Escherichia coli

BACKGROUND

Lipoxygenase (EC. 1.13.11.12, LOX) can catalyze the addition of oxygen into polyunsaturated fatty acids to produce hydroperoxides, which are widely used in the food, chemical, and pharmaceutical industries. In recent years, the heterologous production of LOX by Escherichia coli has attracted extensive attention. However, overexpressed recombinant LOX in E. coli aggregates and forms insoluble inclusion bodies owing to protein misfolding.

RESULTS

In this study, a split green fluorescent protein-based screening method was developed to screen sigma (σ) factors and molecular chaperones for soluble LOX expression. Three mutant libraries of Skp, GroES, and RpoH was analyzed using the high-throughput screening method developed herein, and a series of mutants with significantly higher yield of soluble heterologous LOX were obtained. The soluble expression level of LOX in the isolated mutants increased by 4.2- to 5.3-fold. Further, the highest LOX activity (up to 6240 ± 269 U·g-DCW^-1) was observed in E. coli REopt, with the regulatory factor mutants, RpoH and GroES. Based on RNA-Seq analysis of the selected strains, E. coli Eopt, E. coli Sopt, E. coli Ropt, and wild type, amino acid substitutions in σ factors and molecular chaperones regulated the expression level of genes related to gene replication, recombination, and repair. Furthermore, the regulatory factor mutants were identified to be beneficial to the soluble expression of two other heterologous proteins, amylase and bone morphological protein 12.

CONCLUSION

In this study, a high-throughput screening method was developed for improved soluble LOX expression. The obtained positive mutants of the regulatory factor were analyzed and employed for the expression of other heterologous proteins, thus providing a potential solution for the inclusion-body protein.

Strategies for efficient production of recombinant proteins in Escherichia coli: alleviating the host burden and enhancing protein activity

Escherichia coli, one of the most efficient expression hosts for recombinant proteins (RPs), is widely used in chemical, medical, food and other industries. However, conventional expression strains are unable to effectively express proteins with complex structures or toxicity. The key to solving this problem is to alleviate the host burden associated with protein overproduction and to enhance the ability to accurately fold and modify RPs at high expression levels. Here, we summarize the recently developed optimization strategies for the high-level production of RPs from the two aspects of host burden and protein activity. The aim is to maximize the ability of researchers to quickly select an appropriate optimization strategy for improving the production of RPs.

Overexpression and kinetic analysis of Ideonella sakaiensis PETase for polyethylene terephthalate (PET) degradation

Ideonella sakaiensis PET hydrolase (IsPETase) is a well-characterized enzyme for effective PET biodegradation. However, the low soluble expression level of the enzyme hampers its practical implementation in the biodegradation of PET. Herein, the expression of IsPETase^Mut, one of the most active mutants of IsPETase obtained so far, was systematically explored in E. coli by adopting a series of strategies. A notable improvement of soluble IsPETase^Mut was observed by using chaperon co-expression and fusion expression systems. Under the optimized conditions, GroEL/ES co-expression system yielded 75 ± 3.4 mg·L^-1 purified soluble IsPETase^Mut (GroEL/ES), and NusA fusion expression system yielded 80 ± 3.7 mg·L^-1 purified soluble NusA-IsPETase^Mut, which are 12.5- and 4.6-fold, respectively, higher than its commonly expression in E. coli. The two purified enzymes were further characterized. The results showed that IsPETase^Mut (GroEL/ES) displayed the same catalytic behavior as IsPETase^Mut, while the fusion of NusA conferred new enzymatic properties to IsPETase^Mut. Although NusA-IsPETase^Mut displayed a lower initial hydrolysis capacity than IsPETase^Mut, it showed a 1.4-fold higher adsorption constant toward PET. Moreover, the product inhibition effect of terephthalic acid (TPA) on IsPETase was reduced with NusA-IsPETase^Mut. Taken together, the latter two catalytic properties of NusA-IsPETase^Mut are more likely to contribute to the enhanced product release by NusA-IsPETase^Mut PET degradation for two weeks.

Factors Affecting the Expression of Recombinant Protein and Improvement Strategies in Chinese Hamster Ovary Cells

Recombinant therapeutic proteins (RTPs) are important parts of biopharmaceuticals. Chinese hamster ovary cells (CHO) have become the main cell hosts for the production of most RTPs approved for marketing because of their high-density suspension growth characteristics, and similar human post-translational modification patterns et al. In recent years, many studies have been performed on CHO cell expression systems, and the yields and quality of recombinant protein expression have been greatly improved. However, the expression levels of some proteins are still low or even difficult-to express in CHO cells. It is urgent further to increase the yields and to express successfully the “difficult-to express” protein in CHO cells. The process of recombinant protein expression of is a complex, involving multiple steps such as transcription, translation, folding processing and secretion. In addition, the inherent characteristics of molecular will also affect the production of protein. Here, we reviewed the factors affecting the expression of recombinant protein and improvement strategies in CHO cells.

Comparative Proteomic Analysis of Psychrophilic vs. Mesophilic Bacterial Species Reveals Different Strategies to Achieve Temperature Adaptation

The old debate of nature (genes) vs. nurture (environmental variables) is once again topical concerning the effect of climate change on environmental microorganisms. Specifically, the Polar Regions are experiencing a drastic increase in temperature caused by the rise in greenhouse gas emissions. This study, in an attempt to mimic the molecular adaptation of polar microorganisms, combines proteomic approaches with a classical microbiological analysis in three bacterial species Shewanella oneidensis, Shewanella frigidimarina, and Psychrobacter frigidicola. Both shewanellas are members of the same genus but they live in different environments. On the other hand, Shewanella frigidimarina and Psychrobacter frigidicola share the same natural environment but belong to a different genus. The comparison of the strategies employed by each bacterial species estimates the contribution of genome vs. environmental variables in the adaptation to temperature. The results show a greater versatility of acclimatization for the genus Shewanella with respect to Psychrobacter. Besides, S. frigidimarina was the best-adapted species to thermal variations in the temperature range 4–30°C and displayed several adaptation mechanisms common with the other two species. Regarding the molecular machinery used by these bacteria to face the consequences of temperature changes, chaperones have a pivoting role. They form complexes with other proteins in the response to the environment, establishing cooperation with transmembrane proteins, elongation factors, and proteins for protection against oxidative damage.

New Global Insights on the Regulation of the Biphasic Life Cycle and Virulence Via ClpP-Dependent Proteolysis in Legionella pneumophila

Legionella pneumophila, an environmental bacterium that parasitizes protozoa, causes Legionnaires’ disease in humans that is characterized by severe pneumonia. This bacterium adopts a distinct biphasic life cycle consisting of a nonvirulent replicative phase and a virulent transmissive phase in response to different environmental conditions. Hence, the timely and fine-tuned expression of growth and virulence factors in a life cycle–dependent manner is crucial for survival and replication. Here, we report that the completion of the biphasic life cycle and bacterial pathogenesis is greatly dependent on the protein homeostasis regulated by caseinolytic protease P (ClpP)-dependent proteolysis. We characterized the ClpP-dependent dynamic profiles of the regulatory and substrate proteins during the biphasic life cycle of L. pneumophila using proteomic approaches and discovered that ClpP-dependent proteolysis specifically and conditionally degraded the substrate proteins, thereby directly playing a regulatory role or indirectly controlling cellular events via the regulatory proteins. We further observed that ClpP-dependent proteolysis is required to monitor the abundance of fatty acid biosynthesis–related protein Lpg0102/Lpg0361/Lpg0362 and SpoT for the normal regulation of L. pneumophila differentiation. We also found that the control of the biphasic life cycle and bacterial virulence is independent. Furthermore, the ClpP-dependent proteolysis of Dot/Icm (defect in organelle trafficking/intracellular multiplication) type IVB secretion system and effector proteins at a specific phase of the life cycle is essential for bacterial pathogenesis. Therefore, our findings provide novel insights on ClpP-dependent proteolysis, which spans a broad physiological spectrum involving key metabolic pathways that regulate the transition of the biphasic life cycle and bacterial virulence of L. pneumophila, facilitating adaptation to aquatic and intracellular niches.

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ClpP is the major determinant of biphasic life cycle–dependent protein turnover.

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ClpP-dependent proteolysis monitors SpoT abundance for cellular differentiation.

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ClpP-dependent regulation of life cycle and bacterial virulence is independent.

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ClpP-dependent proteolysis of T4BSS and effector proteins is vital for virulence.

Association between Chromatin Structural Organization of Peripheral Blood Neutrophils and Self-Perceived Mental Stress: Gray-Level Co-occurrence Matrix Analysis

Methods based on the evaluation of textural patterns in microscopy, such as the “gray-level co-occurrence matrix” (GLCM) analysis are modern and innovative computer and mathematical algorithms that can be used to quantify subtle structural changes in cells and their organelles. Potential application of GLCM method in the fields of psychophysiology and psychiatry to this date has not been systematically investigated. The main objective of our study was to test the existence and strength of the association between chromatin structural organization of peripheral blood neutrophils and levels of self-perceived mental stress. The research was done on a sample of 100 healthy student athletes, and the Depression, Anxiety, and Stress Scales (DASS-21) were used for the estimation of psychological distress. Chromatin textural homogeneity and uniformity were negatively correlated (p < 0.01) with mental distress and had relatively good discriminatory power in differentiating participants with normal and elevated stress levels. As an addition, we propose the creation of a machine learning model based on binomial logistic regression that uses these and other GLCM features to predict stress elevation. To the best of our knowledge, these results are one of the first to establish the link between neutrophil chromatin structural organization quantified by the GLCM method and indicators of normal psychological functioning.

Amyloid-type Protein Aggregation and Prion-like Properties of Amyloids

This review will focus on the process of amyloid-type protein aggregation. Amyloid fibrils are an important hallmark of protein misfolding diseases and therefore have been investigated for decades. Only recently, however, atomic or near-atomic resolution structures have been elucidated from various in vitro and ex vivo obtained fibrils. In parallel, the process of fibril formation has been studied in vitro under highly artificial but comparatively reproducible conditions. The review starts with a summary of what is known and speculated from artificial in vitro amyloid-type protein aggregation experiments. A partially hypothetic fibril selection model will be described that may be suitable to explain why amyloid fibrils look the way they do, in particular, why at least all so far reported high resolution cryo-electron microscopy obtained fibril structures are in register, parallel, cross-β-sheet fibrils that mostly consist of two protofilaments twisted around each other. An intrinsic feature of the model is the prion-like nature of all amyloid assemblies. Transferring the model from the in vitro point of view to the in vivo situation is not straightforward, highly hypothetic, and leaves many open questions that need to be addressed in the future.