Escherichia coli Proteome Microarrays Identified the Substrates of ClpYQ Protease

Global protein turnover quantification in Escherichia coli reveals cytoplasmic recycling under nitrogen limitation

Protein turnover is critical for proteostasis, but turnover quantification is challenging, and even in well-studied E. coli, proteome-wide measurements remain scarce. Here, we quantify the turnover rates of ~3200 E. coli proteins under 13 conditions by combining heavy isotope labeling with complement reporter ion quantification and find that cytoplasmic proteins are recycled when nitrogen is limited. We use knockout experiments to assign substrates to the known cytoplasmic ATP-dependent proteases. Surprisingly, none of these proteases are responsible for the observed cytoplasmic protein degradation in nitrogen limitation, suggesting that a major proteolysis pathway in E. coli remains to be discovered. Lastly, we show that protein degradation rates are generally independent of cell division rates. Thus, we present broadly applicable technology for protein turnover measurements and provide a rich resource for protein half-lives and protease substrates in E. coli, complementary to genomics data, that will allow researchers to study the control of proteostasis.

A Transient π-π or Cation-π Interaction between Degron and Degrader Dual Residues: A Key Step for the Substrate Recognition and Discrimination in the Processive Degradation of SulA by ClpYQ (HslUV) Protease in Escherichia coli

The Escherichia coli ATP-dependent ClpYQ protease constitutes ClpY ATPase/unfoldase and ClpQ peptidase. The Tyr91st residue within the central pore-I site of ClpY-hexamer is important for unfolding and translocating substrates into the catalytic site of ClpQ. We have identified the degron site (GFIMRP147th) of SulA, a cell-division inhibitor recognized by ClpYQ and that the Phe143rd residue in degron site is necessary for SulA native folded structure. However, the functional association of this degron site with the ClpYQ degrader is unknown. Here, we investigated the molecular insights into substrate recognition and discrimination by the ClpYQ protease. We found that the point mutants ClpYY91FQ, ClpYY91HQ, and ClpYY91WQ, carrying a ring structure at the 91st residue of ClpY, efficiently degraded their natural substrates, evidenced by the suppressed bacterial methyl-methane-sulfonate (MMS) sensitivity, the reduced β-galactosidase activity of cpsB::lacZ, and the lowest amounts of MBP-SulA in both in vivo and in vitro degradation analyses. Alternatively, mimicking the wild-type SulA, SulAF143H, SulAF143K and SulAF143W, harboring a ring structure or a cation side-group in 143rd residue of SulA, were efficiently degraded by ClpYQ in the bacterial cells, also revealing shorter half-lives at 41 °C and higher binding affinities towards ClpY in pull-down assays. Finally, ClpYY91FQ and ClpYY91HQ, were capable of effectively degrading SulAF143H and SulAF143K, highlighting a correspondingly functional interaction between the SulA 143rd and ClpY 91st residues. According to the interchangeable substituted amino acids, our results uniquely indicate that a transient π-π or cation-π interaction between the SulA 143rd and ClpY 91st residues could be aptly gripped between the degron site of substrates and the pore site of proteases (degraders) for substrate recognition and discrimination of the processive degradation.

Whole-genome sequencing analysis of two heat-evolved Escherichia coli strains

BACKGROUND

High temperatures cause a suite of problems for cells, including protein unfolding and aggregation; increased membrane fluidity; and changes in DNA supercoiling, RNA stability, transcription and translation. Consequently, enhanced thermotolerance can evolve through an unknown number of genetic mechanisms even in the simple model bacterium Escherichia coli. To date, each E. coli study exploring this question resulted in a different set of mutations. To understand the changes that can arise when an organism evolves to grow at higher temperatures, we sequenced and analyzed two previously described E. coli strains, BM28 and BM28 ΔlysU, that have been laboratory adapted to the highest E. coli growth temperature reported to date.

RESULTS

We found three large deletions in the BM28 and BM28 ΔlysU strains of 123, 15 and 8.5 kb in length and an expansion of IS10 elements. We found that BM28 and BM28 ΔlysU have considerably different genomes, suggesting that the BM28 culture that gave rise to BM28 and BM28 ΔlysU was a mixed population of genetically different cells. Consistent with published findings of high GroESL expression in BM28, we found that BM28 inexplicitly carries the groESL bearing plasmid pOF39 that was maintained simply by high-temperature selection pressure. We identified over 200 smaller insertions, deletions, single nucleotide polymorphisms and other mutations, including changes in master regulators such as the RNA polymerase and the transcriptional termination factor Rho. Importantly, this genome analysis demonstrates that the commonly cited findings that LysU plays a crucial role in thermotolerance and that GroESL hyper-expression is brought about by chromosomal mutations are based on a previous misinterpretation of the genotype of BM28.

CONCLUSIONS

This whole-genome sequencing study describes genetically distinct mechanisms of thermotolerance evolution from those found in other heat-evolved E. coli strains. Studying adaptive laboratory evolution to heat in simple model organisms is important in the context of climate change. It is important to better understand genetic mechanisms of enhancing thermotolerance in bacteria and other organisms, both in terms of optimizing laboratory evolution methods for various organisms and in terms of potential genetic engineering of organisms most at risk or most important to our societies and ecosystems.

EbfC/YbaB: A Widely Distributed Nucleoid-Associated Protein in Prokaryotes

Genomic compaction is an essential characteristic of living organisms. Nucleoid-associated proteins (NAPs) are a group of small proteins that play crucial roles in chromosome architecture and affect DNA replication, transcription, and recombination by imposing topological alterations in genomic DNA, thereby modulating global gene expression. EbfC/YbaB was first described as a DNA-binding protein of Borrelia burgdorferi that regulates the expression of surface lipoproteins with roles in virulence. Further studies indicated that this protein binds specifically and non-specifically to DNA and colocalises with nucleoids in this bacterium. The data showed that this protein binds to DNA as a homodimer, although it can form other organised structures. Crystallography analysis indicated that the protein possesses domains responsible for protein–protein interactions and forms a “tweezer” structure probably involved in DNA binding. Moreover, sequence analysis revealed conserved motifs that may be associated with dimerisation. Structural analysis also showed that the tridimensional structure of EbfC/YbaB is highly conserved within the bacterial domain. The DNA-binding activity was observed in different bacterial species, suggesting that this protein can protect DNA during stress conditions. These findings indicate that EbfC/YbaB is a broadly distributed NAP. Here, we present a review of the existing data on this NAP.

Protein degradation control and regulation of bacterial survival and pathogenicity: the role of protein degradation systems in bacteria

BACKGROUND

Protein degradation systems play crucial roles in all the kingdoms of life. Their natural function is to eliminate proteins that are improperly synthesized, damaged, aggregated, or short-lived, ensuring the timely and accurate regulation of the response to abrupt environmental changes. Thus, proteolysis plays an important role in protein homeostasis, quality control, and the control of regulatory processes, such as adaptation and cell development. Except for the lysosome, ATPases Associated with various cellular Activities (AAA+) ATPase-protease complex is another major protein degradation system in the cell.

METHODS AND RESULTS

The AAA+ ATPase-protease complex is a giant energy-dependent protease complex found in almost all kinds of cells, including bacteria, archaea and eukarya. Based on sequence analysis of ClpQ (HslV) and 20S proteasome beta subunits, it was found that bacterial ClpQ possess multiple same highly conserved motifs with 20S proteasome beta subunits of archaea and eukaryote. In this review, we also discussed the structure and functional mechanism, protein degradation signals and pathogenic role of proteasome / Clp protease complex in prokaryotes.

CONCLUSION

Bacterial protein degradation systems play important roles in stress tolerance, protein quality control, DNA protection, transcription and pathogenicity of bacteria. But our current knowledge of the bacterial protease system is incomplete, and further research into the Clp protease complex and associated protein degradation signals will extend our understanding of the metabolism, physiology, reproduction, and pathogenicity of bacteria.

Effect of Clp protease from Corynebacterium glutamicum on heterologous protein expression

The protease present in a host may reduce the yield and biological activity of heterologous proteins. In this study, we used protease overexpression and deletion strategies to examine the effect of the Clp protease system in Corynebacterium glutamicum on the recombinant protein and to produce a highly efficient heterologous protein expression host. In this study, we identified seven genes in the Clp protease family in Corynebacterium glutamicum ATCC 13032 through bioinformatics analysis, and studied their effects on the enhanced green fluorescent protein (EGFP) reporter protein. The fluorescence intensity of the knockout strain was significantly higher, and the effect of the clpS deletion strain was the most obvious. To verify the universal effect of the lack of clpS, the excellent industrial strain C. glutamicum 1.15647 was transformed to form recombinant 15647-ΔclpS. Based on the results, 15647-ΔclpS had a more significant effect on improving protein expression. Furthermore, recombinant human teriparatide (rhPTH) and variable domain of heavy chain of heavy-chain antibody (VHH) were selected to verify the universal applicability of the knockout strain for expressing heterologous proteins. Accordingly, we found that protease deficiency could increase the production of heterologous proteins. Finally, through a large-scale fermentation, the 15647-ΔclpS strain was used to produce VHH. Its yield was approximately 530 mg/L, which was 65% higher than that of WT-15647. In this study, a host that could effectively increase heterologous protein expression was successfully obtained.

Applications of Bacterial Degrons and Degraders - Toward Targeted Protein Degradation in Bacteria

A repertoire of proteolysis-targeting signals known as degrons is a necessary component of protein homeostasis in every living cell. In bacteria, degrons can be used in place of chemical genetics approaches to interrogate and control protein function. Here, we provide a comprehensive review of synthetic applications of degrons in targeted proteolysis in bacteria. We describe recent advances ranging from large screens employing tunable degradation systems and orthogonal degrons, to sophisticated tools and sensors for imaging. Based on the success of proteolysis-targeting chimeras as an emerging paradigm in cancer drug discovery, we discuss perspectives on using bacterial degraders for studying protein function and as novel antimicrobials.

Roles of double-loop (130~159 aa and 175~209 aa) in ClpY(HslU)-I domain for SulA substrate degradation by ClpYQ(HslUV) protease in Escherichia coli

An Escherichia coli ATP-dependent two-component protease, ClpYQ(HslUV), targets the SulA molecule, an SOS induced protein. ClpY recognizes, unfolds and translocates the substrates into the proteolytic site of ClpQ for degradation. ClpY is divided into three domains N, I and C. The N domain is an ATPase; the C domain allows for oligomerization, while the I domain coordinates substrate binding. In the ClpYQ complex, two layer pore sites, pore I and II, are in the center of its hexameric rings. However, the actual roles of two outer-loop (130~159 aa, L1 and 175~209 aa, L2) of the ClpY-I domain for the degradation of SulA are unclear. In this study, with ATP, the MBP-SulA molecule was bound to ClpY oligomer(s). ClpYΔL1 (ClpY deleted of loop 1) oligomers revealed an excessive SulA-binding activity. With ClpQ, it showed increased proteolytic activity for SulA degradation. Yet, ClpYΔL2 formed fewer oligomers that retained less proteolytic activity, but still had increased SulA-binding activity. In contrast, ClpYΔpore I had a lower SulA-binding activity. ClpYΔ pore I ΔL2 showed the lowest SulA-binding activity. In addition, ClpY (Q198L, Q200L), with a double point mutation in loop 2, formed stable oligomers. It also had a subtle increase in SulA-binding activity, but displayed less proteolytic activity. As a result, loop 2 has an effect on ClpY oligomerization, substrate binding and delivery. Loop 1 has a role as a gate, to prevent excessive substrate binding. Thus, accordingly, ClpY permits the formation of SulA-ClpY_(6x), with ATP(s), and this complex then docks through ClpQ_(6x) for ultimate proteolytic degradation.

Advances in Analysis of Milk Proteases Activity at Surfaces and in a Volume by Acoustic Methods

This review is focused on the application of surface and volume-sensitive acoustic methods for the detection of milk proteases such as trypsin and plasmin. While trypsin is an important protein of human milk, plasmin is a protease that plays an important role in the quality of bovine, sheep and goat milks. The increased activity of plasmin can cause an extensive cleavage of β-casein and, thus, affect the milk gelation and taste. The basic principles of surface-sensitive acoustic methods, as well as high-resolution ultrasonic spectroscopy (HR-US), are presented. The current state-of-the-art examples of the application of acoustic sensors for protease detection in real time are discussed. The application of the HR-US method for studying the kinetics of the enzyme reaction is demonstrated. The sensitivity of the acoustics biosensors and HR-US methods for protease detection are compared.

Developments and Applications of Functional Protein Microarrays

Protein microarrays are crucial tools in the study of proteins in an unbiased, high-throughput manner, as they allow for characterization of up to thousands of individually purified proteins in parallel. The adaptability of this technology has enabled its use in a wide variety of applications, including the study of proteome-wide molecular interactions, analysis of post-translational modifications, identification of novel drug targets, and examination of pathogen-host interactions. In addition, the technology has also been shown to be useful in profiling antibody specificity, as well as in the discovery of novel biomarkers, especially for autoimmune diseases and cancers. In this review, we will summarize the developments that have been made in protein microarray technology in both in basic and translational research over the past decade. We will also introduce a novel membrane protein array, the GPCR-VirD array, and discuss the future directions of functional protein microarrays.

Bacterial secretion chaperones: the mycobacterial type VII case

Chaperones are central players in maintaining the proteostasis in all living cells. Besides highly conserved generic chaperones that assist protein folding and assembly in the cytosol, additional more specific chaperones have evolved to ensure the successful trafficking of proteins with extra-cytoplasmic locations. Associated with the distinctive secretion systems present in bacteria, different dedicated chaperones have been described that not only keep secretory proteins in a translocation competent state, but often are also involved in substrate targeting to the specific translocation channel. Recently, a new class of such chaperones has been identified that are involved in the specific recognition of substrates transported via the type VII secretion pathway in mycobacteria. In this minireview, we provide an overview of the different bacterial chaperones with a focus on their roles in protein secretion and will discuss in detail the roles of mycobacterial type VII secretion chaperones in substrate recognition and targeting.

Omnipresent Maxwell's demons orchestrate information management in living cells

The development of synthetic biology calls for accurate understanding of the critical functions that allow construction and operation of a living cell. Besides coding for ubiquitous structures, minimal genomes encode a wealth of functions that dissipate energy in an unanticipated way. Analysis of these functions shows that they are meant to manage information under conditions when discrimination of substrates in a noisy background is preferred over a simple recognition process. We show here that many of these functions, including transporters and the ribosome construction machinery, behave as would behave a material implementation of the information-managing agent theorized by Maxwell almost 150 years ago and commonly known as Maxwell's demon (MxD). A core gene set encoding these functions belongs to the minimal genome required to allow the construction of an autonomous cell. These MxDs allow the cell to perform computations in an energy-efficient way that is vastly better than our contemporary computers.

Specific regions of the SulA protein recognized and degraded by the ATP-dependent ClpYQ (HslUV) protease in Escherichia coli

In Escherichia coli, ClpYQ (HslUV) is a two-component ATP-dependent protease, in which ClpQ is the peptidase subunit and ClpY is the ATPase and unfoldase. ClpY functions to recognize protein substrates, and denature and translocate the unfolded polypeptides into the proteolytic site of ClpQ for degradation. However, it is not clear how the natural substrates are recognized by the ClpYQ protease and the mechanism by which the substrates are selected, unfolded and translocated by ClpY into the interior site of ClpQ hexamers. Both Lon and ClpYQ proteases can degrade SulA, a cell division inhibitor, in bacterial cells. In this study, using yeast two-hybrid and in vivo degradation analyses, we first demonstrated that the C-terminal internal hydrophobic region (139^th∼149^th aa) of SulA is necessary for binding and degradation by ClpYQ. A conserved region, GFIMRP, between 142^th and 147^th residues of SulA, were identified among various Gram-negative bacteria. By using MBP-SulA(F143Y) (phenylalanine substituted with tyrosine) as a substrate, our results showed that this conserved residue of SulA is necessary for recognition and degradation by ClpYQ. Supporting these data, MBP-SulA(F143Y), MBP-SulA(F143N) (phenylalanine substituted with asparagine) led to a longer half-life with ClpYQ protease in vivo. In contrast, MBP-SulA(F143D) and MBP-SulA(F143S) both have shorter half-lives. Therefore, in the E. coli ClpYQ protease complex, ClpY recognizes the C-terminal region of SulA, and F143 of SulA plays an important role for the recognition and degradation by ClpYQ protease.

EspH is a hypervirulence factor for Mycobacterium marinum and essential for the secretion of the ESX-1 substrates EspE and EspF

The pathogen Mycobacterium tuberculosis employs a range of ESX-1 substrates to manipulate the host and build a successful infection. Although the importance of ESX-1 secretion in virulence is well established, the characterization of its individual components and the role of individual substrates is far from complete. Here, we describe the functional characterization of the Mycobacterium marinum accessory ESX-1 proteins EccA₁, EspG₁ and EspH, i.e. proteins that are neither substrates nor structural components. Proteomic analysis revealed that EspG₁ is crucial for ESX-1 secretion, since all detectable ESX-1 substrates were absent from the cell surface and culture supernatant in an espG₁ mutant. Deletion of eccA₁ resulted in minor secretion defects, but interestingly, the severity of these secretion defects was dependent on the culture conditions. Finally, espH deletion showed a partial secretion defect; whereas several ESX-1 substrates were secreted in normal amounts, secretion of EsxA and EsxB was diminished and secretion of EspE and EspF was fully blocked. Interaction studies showed that EspH binds EspE and therefore could function as a specific chaperone for this substrate. Despite the observed differences in secretion, hemolytic activity was lost in all M. marinum mutants, implying that hemolytic activity is not strictly correlated with EsxA secretion. Surprisingly, while EspH is essential for successful infection of phagocytic host cells, deletion of espH resulted in a significantly increased virulence phenotype in zebrafish larvae, linked to poor granuloma formation and extracellular outgrowth. Together, these data show that different sets of ESX-1 substrates play different roles at various steps of the infection cycle of M. marinum.

M. tuberculosis is a facultative intracellular pathogen that has an intimate relationship with host macrophages. Proteins secreted by the ESX-1 secretion system play an important role in this interaction, for instance by orchestrating the escape from the phagosome into the cytosol of the macrophage. However, the exact role of the ESX-1 substrates is unknown, due to their complicated interdependency for secretion. Here, we study the function of ESX-1 accessory proteins EccA₁, EspG₁ and EspH in ESX-1 secretion in Mycobacterium marium, the causative agent of fish tuberculosis. We found that these proteins affect the secretion of different substrate classes, which offers an approach to study the roles of these substrate groups. An espG₁ deletion broadly aborts ESX-1 secretion and thus resulted in severe attenuation in a zebrafish model for tuberculosis, whereas EccA₁ is only crucial under specific growth conditions. The most surprising results were obtained for EspH. This protein seems to function as a molecular chaperone for EspE and is as such involved in the secretion of a small subset of ESX-1 substrates. Disruption of espH showed a dual character: whereas this gene is essential for the successful infection of macrophages, deletion of espH resulted in significantly increased virulence in zebrafish larvae. These data convincingly show that different subsets of ESX-1 substrates play different roles at various steps in the mycobacterial infection cycle.

Whole-cell biocatalysts by design

Whole-cell biocatalysts provide unique advantages and have been widely used for the efficient biosynthesis of value-added fine and bulk chemicals, as well as pharmaceutically active ingredients. What is more, advances in synthetic biology and metabolic engineering, together with the rapid development of molecular genetic tools, have brought about a renaissance of whole-cell biocatalysis. These rapid advancements mean that whole-cell biocatalysts can increasingly be rationally designed. Genes of heterologous enzymes or synthetic pathways are increasingly being introduced into microbial hosts, and depending on the complexity of the synthetic pathway or the target products, they can enable the production of value-added chemicals from cheap feedstock. Metabolic engineering and synthetic biology efforts aimed at optimizing the existing microbial cell factories concentrate on improving heterologous pathway flux, precursor supply, and cofactor balance, as well as other aspects of cellular metabolism, to enhance the efficiency of biocatalysts. In the present review, we take a critical look at recent developments in whole-cell biocatalysis, with an emphasis on strategies applied to designing and optimizing the organisms that are increasingly modified for efficient production of chemicals.