A natural product from Streptomyces targets PhoP and exerts antivirulence action against Salmonella enterica.

Background: The overprescription and misuse of classical antimicrobial compounds to treat gastrointestinal or systemic salmonellosis have been accelerating the surge of antibiotic-recalcitrant bacterial populations, posing a major public health challenge. Therefore, alternative therapeutic approaches to treat Salmonella infections are urgently required.

Objectives: To identify and characterize actinobacterial secreted compounds with inhibitory properties against the Salmonella enterica PhoP/PhoQ signal transduction system, crucial for virulence regulation.

The p105 NF-ĸB precursor is a pseudo substrate of the ubiquitin ligase FBXO7, and its binding to the ligase stabilizes it and results in stimulated cell proliferation.

The NF-κB transcription factor is involved in inflammation and cell proliferation, survival, and transformation. It is a heterodimer made of p50 or p52 and a member of the Rel family of proteins. p50 and p52 are derived from limited ubiquitin- and proteasome-mediated proteolytic processing of the larger precursors p105 and p100, respectively.

De novo macrocyclic peptides that specifically modulate Lys48-linked ubiquitin chains.

A promising approach in cancer therapy is to find ligands that directly bind ubiquitin (Ub) chains. However, finding molecules capable of tightly and specifically binding Ub chains is challenging given the range of Ub polymer lengths and linkages and their subtle structural differences. Here, we use total chemical synthesis of proteins to generate highly homogeneous Ub chains for screening against trillion-member macrocyclic peptide libraries (RaPID system).

Diverse fate of ubiquitin chain moieties: The proximal is degraded with the target, and the distal protects the proximal from removal and recycles.

One of the enigmas in the ubiquitin (Ub) field is the requirement for a poly-Ub chain as a proteasomal targeting signal. The canonical chain appears to be longer than the distance between the two Ub-binding proteasomal receptors. Furthermore, genetic manipulation has shown that one receptor subunit is sufficient, which suggests that a single Ub can serve as a degradation signal.

Numerous proteins with unique characteristics are degraded by the 26S proteasome following monoubiquitination.

The "canonical" proteasomal degradation signal is a substrate-anchored polyubiquitin chain. However, a handful of proteins were shown to be targeted following monoubiquitination. In this study, we established-in both human and yeast cells-a systematic approach for the identification of monoubiquitination-dependent proteasomal substrates.

Modification of the inflammatory mediator LRRFIP2 by the ubiquitin-like protein FAT10 inhibits its activity during cellular response to LPS.

FAT10 is a ubiquitin-like protein made of two tandem, head-to-tail, ubiquitin domains. It is known to covalently modify proteins in a mechanism similar, though not identical, to that of other ubiquitin-like proteins. The lack of known physiological substrates covalently conjugated by the protein made it difficult to unravel its biological functions.

FAT10 is a proteasomal degradation signal that is itself regulated by ubiquitination.

FAT10 is a ubiquitin-like protein modifier that is induced in vertebrates following certain inflammatory stimuli. Its functions and the repertoire of its target substrates have remained elusive. In contrast to ubiquitin, its cellular abundance is tightly controlled by both transcriptional and posttranslational regulation, and it was reported to be rapidly degraded by the proteasome.

Epstein-Barr virus-encoded EBNA-5 forms trimolecular protein complexes with MDM2 and p53 and inhibits the transactivating function of p53.

We report that MDM2, a negative regulator of p53, can bind to EBNA-5. Using GST pull-down assay, immunoprecipitation, surface plasmon resonance and immunostaining of lymphoblastoid cells, we found that trimolecular complexes are formed between EBNA-5, MDM2 and p53, where MDM2 serves as a bridge. The EBNA-5 binding to MDM2 counteracted destabilizing effect of the latter on the p53.

The N-terminal domain of MyoD is necessary and sufficient for its nuclear localization-dependent degradation by the ubiquitin system.

A growing number of proteins, including the myogenic transcription factor MyoD, are targeted for proteasomal degradation after N-terminal ubiquitination (NTU) where the first ubiquitin moiety is conjugated to the N-terminal residue rather than to an internal lysine. NTU might be essential in targeting both lysine-containing and naturally occurring lysine-less proteins such as p16(INK4a) and p14(ARF); however, the mechanisms that underlie this process are largely unknown. Specifically, the recognition motif(s) in the target substrates and the ubiquitin ligase(s) that catalyze NTU are still obscure.

c-Abl regulates p53 levels under normal and stress conditions by preventing its nuclear export and ubiquitination.

The p53 protein is subject to Mdm2-mediated degradation by the ubiquitin-proteasome pathway. This degradation requires interaction between p53 and Mdm2 and the subsequent ubiquitination and nuclear export of p53. Exposure of cells to DNA damage results in the stabilization of the p53 protein in the nucleus.

Mechanisms of ubiquitin-mediated, limited processing of the NF-kappaB1 precursor protein p105.

In most cases, target proteins of the ubiquitin system are completely degraded. In several exceptions, such as the first step in the activation of the transcriptional regulator NF-kappaB, the substrate, the precursor protein p105, is processed in a limited manner to yield the active subunit p50. p50 is derived from the N-terminal domain of p105, whereas the C-terminal domain is degraded.

SCF(beta)(-TrCP) ubiquitin ligase-mediated processing of NF-kappaB p105 requires phosphorylation of its C-terminus by IkappaB kinase.

Processing of the p105 precursor to form the active subunit p50 of the NF-kappaB transcription factor is a unique case in which the ubiquitin system is involved in limited processing rather than in complete destruction of the target substrate. A glycine-rich region along with a downstream acidic domain have been demonstrated to be essential for processing. Here we demonstrate that following IkappaB kinase (IkappaK)-mediated phosphorylation, the C-terminal domain of p105 (residues 918-934) serves as a recognition motif for the SCF(beta)(-TrCP) ubiquitin ligase.

Identification of the ubiquitin carrier proteins, E2s, involved in signal-induced conjugation and subsequent degradation of IkappaBalpha.

The last step in the activation of the transcription factor NF-kappaB is signal-induced, ubiquitin- and proteasome-mediated degradation of the inhibitor IkappaBalpha. Although most of the components involved in the activation and degradation pathways have been identified, the ubiquitin carrier proteins (E2) have remained elusive. Here we show that the two highly homologous members of the UBCH5 family, UBCH5b and UBCH5c, and CDC34/UBC3, the mammalian homolog of yeast Cdc34/Ubc3, are the E2 enzymes involved in the process.

Basal and human papillomavirus E6 oncoprotein-induced degradation of Myc proteins by the ubiquitin pathway.

We have previously shown that the degradation of c-myc and N-myc in vitro is mediated by the ubiquitin system. However, the role of the system in targeting the myc proteins in vivo and the identity of the conjugating enzymes and possible ancillary proteins involved has remained obscure. Here we report that the degradation of the myc proteins in cells is inhibited by lactacystin and MG132, two inhibitors of the 20S proteasome.

Role of UEV-1, an inactive variant of the E2 ubiquitin-conjugating enzymes, in in vitro differentiation and cell cycle behavior of HT-29-M6 intestinal mucosecretory cells.

By means of differential RNA display, we have isolated a cDNA corresponding to transcripts that are down-regulated upon differentiation of the goblet cell-like HT-29-M6 human colon carcinoma cell line. These transcripts encode proteins originally identified as CROC-1 on the basis of their capacity to activate transcription of c-fos. We show that these proteins are similar in sequence, and in predicted secondary and tertiary structure, to the ubiquitin-conjugating enzymes, also known as E2.

Ubiquitin-dependent degradation of certain protein substrates in vitro requires the molecular chaperone Hsc70.

Degradation of a protein via the ubiquitin system involves two discrete steps, signaling by covalent conjugation of multiple moieties of ubiquitin and degradation of the tagged substrate. Conjugation is catalyzed via a three-step mechanism that involves three distinct enzymes that act successively: E1, E2, and E3. The first two enzymes catalyze activation of ubiquitin and transfer of the activated moiety to E3, respectively.

Isolation, characterization, and partial purification of a novel ubiquitin-protein ligase, E3. Targeting of protein substrates via multiple and distinct recognition signals and conjugating enzymes.

Degradation of a protein via the ubiquitin system involves two discrete steps, conjugation of ubiquitin to the substrate and degradation of the adduct. Conjugation follows a three-step mechanism. First, ubiquitin is activated by the ubiquitin-activating enzyme, E1.

Degradation of ornithine decarboxylase by the mammalian and yeast 26S proteasome complexes requires all the components of the protease.

Ornithine decarboxylase (ODC), a key enzyme in the biosynthesis of polyamines, is an extremely short-lived protein. This attribute is important for the regulation of the activity of the enzyme and implies that the mechanisms involved in its degradation play an important role in the control of the cellular processes in which the enzyme is involved. Recently, it has been shown that ODC is degraded by the 26S proteasome complex in a process that requires antizyme, but not ubiquitin.

Complete reconstitution of conjugation and subsequent degradation of the tumor suppressor protein p53 by purified components of the ubiquitin proteolytic system.

The wild-type tumor suppressor protein p53 is a short-lived protein that plays important roles in regulation of cell cycle, differentiation, and survival. Mutations that inactivate or alter the tumor suppressor activity of the protein seem to be the most common genetic change in human cancer and are frequently associated with changes in its stability. The ubiquitin system has been implicated in the degradation of p53 both in vivo and in vitro.

Degradation of the tumor suppressor protein p53 by the ubiquitin-mediated proteolytic system requires a novel species of ubiquitin-carrier protein, E2.

The tumor suppressor protein p53 is extremely unstable in most cell lines. In contrast, many mutant and oncogenic species of the protein are stable. The degradation of p53 in vivo requires metabolic energy; however, the proteolytic system(s) involved have not been identified.

Degradation of nuclear oncoproteins by the ubiquitin system in vitro.

Nuclear oncoproteins are among the most rapidly degraded intracellular proteins. Previous work has implicated the ubiquitin-mediated proteolytic system in the turnover of short-lived intracellular proteins. In the present study, we have evaluated the potential role of the ubiquitin system in the degradation of the specific nuclear oncoproteins encoded by the N-myc, c-myc, c-fos, p53 and E1A genes.