Hierarchical Model for the Role of J-Domain Proteins in Distinct Cellular Functions

Systems engineering of Escherichia coli for high-level glutarate production from glucose

Glutarate is a key monomer in polyester and polyamide production. The low efficiency of the current biosynthetic pathways hampers its production by microbial cell factories. Herein, through metabolic simulation, a lysine-overproducing E. coli strain Lys5 is engineered, achieving titer, yield, and productivity of 195.9 g/L, 0.67 g/g glucose, and 5.4 g/L·h, respectively. Subsequently, the pathway involving aromatic aldehyde synthase, monoamine oxidase, and aldehyde dehydrogenase (AMA pathway) is introduced into E. coli Lys5 to produce glutarate from glucose. To enhance the pathway's efficiency, rational mutagenesis on the aldehyde dehydrogenase is performed, resulting in the development of variant Mu5 with a 50-fold increase in catalytic efficiency. Finally, a glutarate tolerance gene cbpA is identified and genomically overexpressed to enhance glutarate productivity. With enzyme expression optimization, the glutarate titer, yield, and productivity of E. coli AMA06 reach 88.4 g/L, 0.42 g/g glucose, and 1.8 g/L·h, respectively. These findings hold implications for improving glutarate biosynthesis efficiency in microbial cell factories.

WGS-based screening of the co-chaperone protein DjlA-induced curved DNA binding protein A (CbpA) from a new multidrug-resistant zoonotic mastitis-causing Klebsiella pneumoniae strain: a novel molecular target of selective flavonoids

The research aimed to establish a multidrug-resistant Klebsiella pneumoniae-induced genetic model for mastitis considering the alternative mechanisms of the DjlA-mediated CbpA protein regulation. The Whole Genome Sequencing of the newly isolated K. pneumoniae strain was conducted to annotate the frequently occurring antibiotic resistance and virulence factors following PCR and MALDI-TOF mass-spectrophotometry. Co-chaperon DjlA was identified and extracted via restriction digestion on PAGE. Based on the molecular string property analysis of different DnaJ and DnaK type genes, CbpA was identified to be regulated most by the DjlA protein during mastitis. Based on the quantum tunnel-cluster profiles, CbpA was modeled as a novel target for diversified biosynthetic, and chemosynthetic compounds. Pharmacokinetic and pharmacodynamic analyses were conducted to determine the maximal point-specificity of selective flavonoids in complexing with the CbpA macromolecule at molecular docking. The molecular dynamic simulation (100 ns) of each of the flavonoid-protein complexes was studied regarding the parameters RMSD, RMSF, Rg, SASA, MMGBSA, and intramolecular hydrogen bonds; where all of them resulted significantly. To ratify all the molecular dynamic simulation outputs, the potential stability of the flavonoids in complexing with CbpA can be remarked as Quercetin > Biochanin A > Kaempherol > Myricetin, which were all significant in comparison to the control Galangin. Finally, a comprehensive drug-gene interaction pathway for each of the flavonoids was developed to determine the simultaneous and quantitative-synergistic effects of different operons belonging to the DnaJ-type proteins on the metabolism of the tested pharmacophores in CbpA. Considering all the in vitro and in silico parameters, DjlA-mediated CbpA can be a novel target for the tested flavonoids as the potential therapeutics of mastitis as futuristic drugs.

Bacterial J-Domains with C-Terminal Tags Contact the Substrate Binding Domain of DnaK and Sequester Chaperone Activity

Functional interactions between the molecular chaperone DnaK and cofactor J-proteins (DnaJs), as well as their homologs, are crucial to the maintenance of proteostasis across cell types. In the bacterial pathogen Mycobacterium tuberculosis, DnaK-DnaJ interactions are essential for cell growth and represent potential targets for antibiotic or adjuvant development. While the N-terminal J-domains of J-proteins are known to form important contacts with DnaK, C-terminal domains have varied roles. Here, we have studied the effect of adding C-terminal tags to N-terminal J-domain truncations of mycobacterial DnaJ1 and DnaJ2 to promote additional interactions with DnaK. We found that His6 tags uniquely promote binding to additional sites in the substrate binding domain at the C-terminus of DnaK. Other C-terminal tags attached to J-domains, even peptides known to interact with DnaK, do not produce the same effects. Expression of C-terminally modified DnaJ1 or DnaJ2 J-domains in mycobacterial cells suppresses chaperone activity following proteotoxic stress, which is exaggerated in the presence of a small-molecule DnaK inhibitor. Hence, this work uncovers genetically encodable J-protein variants that may be used to study chaperone-cofactor interactions in other organisms.

CsgI (YccT) Is a Novel Inhibitor of Curli Fimbriae Formation in Escherichia coli Preventing CsgA Polymerization and Curli Gene Expression

Curli fimbriae are amyloids-found in bacteria (Escherichia coli)-that are involved in solid-surface adhesion and bacterial aggregation during biofilm formation. The curli protein CsgA is coded by a csgBAC operon gene, and the transcription factor CsgD is essential to induce its curli protein expression. However, the complete mechanism underlying curli fimbriae formation requires elucidation. Herein, we noted that curli fimbriae formation was inhibited by yccT-i.e., a gene that encodes a periplasmic protein of unknown function regulated by CsgD. Furthermore, curli fimbriae formation was strongly repressed by CsgD overexpression caused by a multicopy plasmid in BW25113-the non-cellulose-producing strain. YccT deficiency prevented these CsgD effects. YccT overexpression led to intracellular YccT accumulation and reduced CsgA expression. These effects were addressed by deleting the N-terminal signal peptide of YccT. Localization, gene expression, and phenotypic analyses revealed that YccT-dependent inhibition of curli fimbriae formation and curli protein expression was mediated by the two-component regulatory system EnvZ/OmpR. Purified YccT inhibited CsgA polymerization; however, no intracytoplasmic interaction between YccT and CsgA was detected. Thus, YccT-renamed CsgI (curli synthesis inhibitor)-is a novel inhibitor of curli fimbriae formation and has a dual role as an OmpR phosphorylation modulator and CsgA polymerization inhibitor.

A DnaK(Hsp70) Chaperone System Connects Type IV Pilus Activity to Polysaccharide Secretion in Cyanobacteria

Surface motility powered by type IV pili (T4P) is widespread among bacteria, including the photosynthetic cyanobacteria. This form of movement typically requires the deposition of a motility-associated polysaccharide, and several studies indicate that there is complex coregulation of T4P motor activity and polysaccharide production, although a mechanistic understanding of this coregulation is not fully defined. Here, using a combination of genetic, comparative genomic, transcriptomic, protein-protein interaction, and cytological approaches in the model filamentous cyanobacterium N. punctiforme, we provided evidence that a DnaK-type chaperone system coupled the activity of the T4P motors to the production of the motility-associated hormogonium polysaccharide (HPS). The results from these studies indicated that DnaK1 and DnaJ3 along with GrpE comprised a chaperone system that interacted specifically with active T4P motors and was required to produce HPS. Genomic conservation in cyanobacteria and the conservation of the protein-protein interaction network in the model unicellular cyanobacterium Synechocystis sp. strain PCC 6803 imply that this system is conserved among nearly all motile cyanobacteria and provides a mechanism to coordinate polysaccharide secretion and T4P activity in these organisms.

Potentiation of the activity of Escherichia coli chaperone DnaJ by tailing hyper-acidic minipeptides

The chaperone network plays an essential role in cellular protein homeostasis. However, some core components often coaggregate with misfolded proteins for sequestration and dysfunction, leading to abnormal cell proteostasis, aggregation-associated disorders, and poor solubility of overexpressed recombinant proteins. Among them, DnaJ or its ortholog, an obligate co-chaperone in the tripartite DnaK-DnaJ-GrpE system, is of more implications, probably due to its intrinsic propensity for aggregation. Herein, we potentiated the activity of Escherichia coli DnaJ by using hyper-acidified protein fusion strategy. We found DnaJ did possess only a moderate solubility that could be remarkably improved by fusing hyper-acidic minipeptides. Most importantly, we revealed the hyper-acidified DnaJ with a fusion tail could outperform its native form (significantly up to 2.1-fold) to enhance the solubility of target proteins and meanwhile appropriately impart them an elevated activity. These results suggest the hyper-acidified DnaJs can chaperone target proteins with correct folding into a truly soluble and active form. Moreover, we showed these hyper-acidified DnaJ variants could surpass its prototype to confer E. coli or yeast an enhanced heat tolerance, and DnaJ itself could be solubilized by its hyper-acidified fusion cognates. Finally, we discussed the overall mechanism for DnaJ activity potentiation mediated by hyper-acidic tailing fusion.