Highly Sensitive Labeling, Clickable Functionalization, and Glycoengineering of the MUC1 Neighboring System

This study introduces a novel wash-type affinity-primed proximity labeling (WAPL) strategy for labeling and surface engineering of the MUC1 protein neighboring system. The strategy entails the utilization of peroxidase in conjunction with a MUC1-selective aptamer, facilitating targeted binding to MUC1 and inducing covalent labeling of the protein neighboring system. This study reveals a novel finding that the WAPL strategy demonstrates superior labeling efficiency in comparison to nonwash-type affinity-primed proximity labeling, marking the first instance of such observations. The WAPL strategy provides signal amplification by converting a single recognition event into multiple covalent labeling events, thereby improving the detection sensitivity for subtle changes in MUC1. The WAPL platform employs two levels of labeling upgrades, modifying the biotin handles of the conventional labeling substrate, biotin-phenol. The first level involves a range of clickable molecules, facilitating dibenzoazacyclooctynylation, alkynylation, and trans-cyclooctenylation of the protein neighboring system. The second level utilizes lactose as a post-translational modification model, enabling rapid and reliable glycoengineering of the MUC1 neighboring system while remaining compatible with cell-based assays. The implementation of the WAPL strategy in protein neighboring systems has resulted in the establishment of a versatile platform that can effectively facilitate diverse monitoring and regulation techniques. This platform offers valuable insights into the regulation of relevant signaling pathways and promotes the advancement of novel therapeutic approaches, thereby bringing substantial implications for human health.

Frameshift Mutation Confers Function as Virulence Factor to Leucine-Rich Repeat Protein from Acidovorax avenae

Many plant pathogens inject type III (T3SS) effectors into host cells to suppress host immunity and promote successful infection. The bacterial pathogen Acidovorax avenae causes brown stripe symptom in many species of monocotyledonous plants; however, individual strains of each pathogen infect only one host species. T3SS-deleted mutants of A. avenae K1 (virulent to rice) or N1141 (virulent to finger millet) caused no symptom in each host plant, suggesting that T3SS effectors are involved in the symptom formation. To identify T3SS effectors as virulence factors, we performed whole-genome and predictive analyses. Although the nucleotide sequence of the novel leucine-rich repeat protein (Lrp) gene of N1141 had high sequence identity with K1 Lrp, the amino acid sequences of the encoded proteins were quite different due to a 1-bp insertion within the K1 Lrp gene. An Lrp-deleted K1 strain (KΔLrp) did not cause brown stripe symptom in rice (host plant for K1); by contrast, the analogous mutation in N1141 (NΔLrp) did not interfere with infection of finger millet. In addition, NΔLrp retained the ability to induce effector-triggered immunity (ETI), including hypersensitive response cell death and expression of ETI-related genes. These data indicated that K1 Lrp functions as a virulence factor in rice, whereas N1141 Lrp does not play a similar role in finger millet. Yeast two-hybrid screening revealed that K1 Lrp interacts with oryzain α, a pathogenesis-related protein of the cysteine protease family, whereas N1141 Lrp, which contains LRR domains, does not. This specific interaction between K1 Lrp and oryzain α was confirmed by Bimolecular fluorescence complementation assay in rice cells. Thus, K1 Lrp protein may have acquired its function as virulence factor in rice due to a frameshift mutation.

Peroxidase-mediated dealkylation of tamoxifen, detected by electrospray ionization-mass spectrometry, and activation to form DNA adducts

Tamoxifen (TAM) is extensively used for the treatment and prevention of breast cancer. Associated with TAM treatment is a two- to eightfold increase in risk of endometrial cancer. To understand the mechanisms associated with this increased risk several pathways for TAM metabolism and DNA adduct formation have been studied. The purpose of this study was to investigate the role of peroxidase enzymes in the metabolism of TAM and its activation to form DNA adducts. Using advanced tandem mass spectrometry we have investigated the peroxidase-mediated metabolism of TAM. Incubation of TAM with horseradish peroxidase (HRP) and H(2)O(2) produced multiple metabolites. Electrospray ionization-MS/MS analysis of the metabolites demonstrated a peak at 301.3m/z with daughter ions at 183.0, 166.9, 128.9, and 120.9m/z, which identified the metabolite as metabolite E (ME). The levels of ME were significantly inhibited by the addition of ascorbic acid to the incubation mixture. Co-incubation of either TAM or ME and DNA with HRP and H(2)O(2) produced three DNA adducts with a RAL of 1.97±0.01×10(-7) and 8.45±2.7×10(-7). Oxidation of ME with MnO(2) produced metabolite E quinone methide (MEQM). Furthermore, incubation of either TAM or ME with HRP and H(2)O(2) resulted in formation of MEQM. Reaction of calf thymus DNA with MEQM produced three DNA adducts with a RAL of 9.8±1.0×10(-7). Rechromatography analyses indicated that DNA adducts 1, 2, and 3 formed in the HRP activation of either TAM or ME were the same as those formed by the chemical reaction of DNA with MEQM. The results of these studies demonstrate that peroxidase enzymes can both metabolize TAM to form the primary metabolite ME and activate ME to a quinone methide intermediate, which reacts with DNA to form adducts. It is possible that peroxidase enzymes or peroxidase-like activity in endometrium could contribute to the formation of DNA damage and genotoxic effects in endometrium after TAM administration.

Measurement of peroxiredoxin activity

Peroxiredoxins are cysteine-dependent peroxidases that react with hydrogen peroxide, larger hydroperoxide substrates, and peroxynitrite. Protocols are provided to measure Prx activity with peroxide by (1) a coupled reaction with NADPH, thioredoxin reductase, and thioredoxin, (2) the direct monitoring of thioredoxin oxidation, (3) competition with horseradish peroxidase, and (4) peroxide consumption using the FOX assay.

Enzyme-linked enzyme-binding assay for Pin1 WW domain ligands

Peptidyl prolyl cis-trans isomerase (PPIase) interacting with NIMA-1 (Pin1) catalyzes the cis-trans isomerization of pSer/pThr-Pro amide bonds. Pin1 is a two-domain protein that represents a promising target for the treatment of cancer. Both domains of Pin1 bind the pSer/pThr-Pro motif; PPIase enzymatic activity occurs in the catalytic domain, and the WW domain acts as a recognition module for the pSer/pThr-Pro motif. An assay we call an enzyme-linked enzyme-binding assay (ELEBA) was developed to measure the K(d) of ligands that bind selectively to the WW domain. A ligand specific for the WW domain of Pin1 was covalently immobilized in a 96-well plate. Commercially available Pin1 conjugated to horseradish peroxidase was used for chemiluminescent detection of ligands that block the association of the WW domain with immobilized ligand. The peptide ligands were derived from the cell cycle regulatory phosphatase, Cdc25c, residues 45-50. The K(d) values for Fmoc-VPRpTPVGGGK-NH2 and Ac-VPRpTPV-NH2 were determined to be 36+/-4 and 110+/-30 microM, respectively. The ELEBA offers a selective approach for detecting ligands that bind to the Pin1 WW domain, even in the presence of the catalytic domain. This method may be applied to any dual specificity, multidomain protein.

Multiple activities of the plant pathogen type III effector proteins WtsE and AvrE require WxxxE motifs

The broadly conserved AvrE-family of type III effectors from gram-negative plant-pathogenic bacteria includes important virulence factors, yet little is known about the mechanisms by which these effectors function inside plant cells to promote disease. We have identified two conserved motifs in AvrE-family effectors: a WxxxE motif and a putative C-terminal endoplasmic reticulum membrane retention/retrieval signal (ERMRS). The WxxxE and ERMRS motifs are both required for the virulence activities of WtsE and AvrE, which are major virulence factors of the corn pathogen Pantoea stewartii subsp. stewartii and the tomato or Arabidopsis pathogen Pseudomonas syringae pv. tomato, respectively. The WxxxE and the predicted ERMRS motifs are also required for other biological activities of WtsE, including elicitation of the hypersensitive response in nonhost plants and suppression of defense responses in Arabidopsis. A family of type III effectors from mammalian bacterial pathogens requires WxxxE and subcellular targeting motifs for virulence functions that involve their ability to mimic activated G-proteins. The conservation of related motifs and their necessity for the function of type III effectors from plant pathogens indicates that disturbing host pathways by mimicking activated host G-proteins may be a virulence mechanism employed by plant pathogens as well.

Control of Virulence and Pathogenicity Genes of Ralstonia Solanacearum by an Elaborate Sensory Network

Ralstonia solanacearum causes a lethal bacterial wilt disease of diverse plants. It invades the xylem vessels of roots and disseminates into the stem where it multiplies and wilts by excessive exopolysaccharide production. Many of its key extracytoplasmic virulence and pathogenicity factors are transcriptionally controlled by an extensive network of distinct, interacting signal transduction pathways. The core of this sensory network is the five-gene Phc system that regulates exopolysaccharide, cell-wall-degrading exoenzymes, and other factors in response to a self-produced signal molecule that monitors the pathogen's growth status and environment. Four additional environmentally responsive two-component systems work independently and with the Phc system to fine-tune virulence gene expression. Another critical system is Prh which transduces plant cell-derived signals through a six-gene cascade to activate deployment of the Type III secretion pathway encoded by the hrp pathogenicity genes. Here I summarize knowledge about the regulated targets, signal transduction mechanisms, and crosstalk between Phc, Prh, and other systems. I also provide insight into why R. solanacearum has evolved such a sophisticated sensory apparatus, and how it functions in disease.