Tsg101 UEV Research Articles

Tsg101 UEV Interaction with Nedd4 HECT Relieves E3 Ligase Auto-Inhibition, Promoting HIV-1 Assembly and CA-SP1 Maturation Cleavage

Tsg101, a component of the endosomal sorting complex required for transport (ESCRT), is responsible for recognition of events requiring the machinery, as signaled by cargo tagging with ubiquitin (Ub), and for recruitment of downstream acting subunits to the site. Although much is known about the latter function, little is known about its role in the earlier event. The N-terminal domain of Tsg101 is a structural homologue of Ub conjugases (E2 enzymes) and the protein associates with Ub ligases (E3 enzymes) that regulate several cellular processes including virus budding. A pocket in the domain recognizes a motif, PT/SAP, that permits its recruitment. PT/SAP disruption makes budding dependent on Nedd4L E3 ligases. Using HIV-1 encoding a PT/SAP mutation that makes budding Nedd4L-dependent, we identified as critical for rescue the residues in the catalytic (HECT) domain of the E3 enzyme that lie in proximity to sites in Tsg101 that bind Ub non-covalently. Mutation of these residues impaired rescue by Nedd4L but the same mutations had no apparent effect in the context of a Nedd4 isomer, Nedd4-2s, whose N-terminal (C2) domain is naturally truncated, precluding C2-HECT auto-inhibition. Surprisingly, like small molecules that disrupt Tsg101 Ub-binding, small molecules that interfered with Nedd4 substrate recognition arrested budding at an early stage, supporting the conclusion that Tsg101–Ub–Nedd4 interaction promotes enzyme activation and regulates Nedd4 signaling for viral egress. Tsg101 regulation of E3 ligases may underlie its broad ability to function as an effector in various cellular activities, including viral particle assembly and budding.

Phage display identification of high-affinity ligands for human TSG101-UEV: A structural and thermodynamic study of PTAP recognition

The ubiquitin E2 variant domain of TSG101 (TSG101-UEV) plays a pivotal role in protein sorting and virus budding by recognizing PTAP motifs within ubiquitinated proteins. Disrupting TSG101-UEV/PTAP interactions has emerged as a promising strategy for the development of novel host-oriented antivirals with a broad spectrum of action. Nonetheless, finding inhibitors with good properties as therapeutic agents remains a challenge since the key determinants of binding affinity and specificity are still poorly understood. Here we present a detailed thermodynamic, structural, and dynamic characterization viral PTAP Late domain recognition by TSG101-UEV, combining isothermal titration calorimetry, X-ray diffraction structural studies, molecular dynamics simulations, and computational analysis of intramolecular communication pathways. Our analysis highlights key contributions from conserved hydrophobic contacts and water-mediated hydrogen bonds at the PTAP binding interface. We have identified additional electrostatic hotspots adjacent to the core motif that modulate affinity. Using competitive phage display screening we have improved affinity by 1–2 orders of magnitude, producing novel peptides with low micromolar affinities that combine critical elements found in the best natural binders. Molecular dynamics simulations revealed that optimized peptides engage new pockets on the UEV domain surface. This study provides a comprehensive view of the molecular forces directing TSG101-UEV recognition of PTAP motifs, revealing that binding is governed by conserved structural elements yet tuneable through targeted optimization. These insights open new venues to design inhibitors targeting TSG101-dependent pathways with potential application as novel broad-spectrum antivirals.

Structural Relationships to Efficacy for Prazole-Derived Antivirals.

Here, an in vitro characterization of a family of prazole derivatives that covalently bind to the C73 site on Tsg101 and assay their ability to inhibit viral particle production is presented. Structurally, increased steric bulk on the 4-pyridyl of the prazole expands the prazole site on the UEV domain toward the β-hairpin in the Ub-binding site and is coupled to increased inhibition of virus-like particle production in HIV-1. Increased bulk also increased toxicity, which is alleviated by increasing flexibility. Further, the formation of a novel secondary Tsg101 adduct for several of the tested compounds and the commercial drug lansoprazole. The secondary adduct involved the loss of the 4-pyridyl substituent to form an irreversible species, with implications for increasing the half-life of the active species or its specificity toward Tsg101 UEV. It is also determined that sulfide derivatives display effective viral inhibition, presumably through cellular sulfoxidation, allowing for delayed conversion within the cellular environment, and identify SARS-COV-2 as a target of prazole inhibition. These results open multiple avenues for the design of prazole derivatives for antiviral applications.

Evaluation of affinity-purification coupled to mass spectrometry approaches for capture of short linear motif-based interactions

Low affinity and transient protein-protein interactions, such as short linear motif (SLiM)-based interactions, require dedicated experimental tools for discovery and validation. Here, we evaluated and compared biotinylated peptide pulldown and protein interaction screen on peptide matrix (PRISMA) coupled to mass-spectrometry (MS) using a set of peptides containing interaction motifs. Eight different peptide sequences that engage in interactions with three distinct protein domains (KEAP1 Kelch, MDM2 SWIB, and TSG101 UEV) with a wide range of affinities were tested. We found that peptide pulldown can be an effective approach for SLiM validation, however, parameters such as protein abundance and competitive interactions can prevent the capture of known interactors. The use of tandem peptide repeats improved the capture and preservation of some interactions. When testing PRISMA, it failed to provide comparable results for model peptides that successfully pulled down known interactors using biotinylated peptide pulldown. Overall, in our hands, we find that albeit more laborious, biotin-peptide pulldown was more successful in terms of validation of known interactions. Our results highlight that the tested affinity-capture MS-based methods for validation of SLiM-based interactions from cell lysates are suboptimal, and we identified parameters for consideration for method development.

Cyclic Peptide Inhibitors of the Tsg101 UEV Protein Interactions Refined through Global Docking and Gaussian Accelerated Molecular Dynamics Simulations.

Tsg101 UEV domain proteins are potential targets for virus infection therapy, especially for HIV and Ebola viruses. Peptides are key in curbing virus transmission, and cyclic peptides have a greater survival time than their linear peptides. To date, the accurate prediction of cyclic peptide-protein receptors binding conformations still is challenging because of high peptide flexibility. Here, a useful approach combined the global peptide docking, Gaussian accelerated molecular dynamics (GaMD), two-dimensional (2D) potential of mean force (PMF), normal molecular dynamics (cMD), and solvated interaction energy (SIE) techniques. Then we used this approach to investigate the binding conformations of UEV domain proteins with three cyclic peptides inhibitors. We reported the possible cyclic peptide-UEV domain protein binding conformations via 2D PMF free energy profiles and SIE free energy calculations. The residues Trp145, Tyr147, and Trp148 of the native cyclic peptide (CP1) indeed play essential roles in the cyclic peptides-UEV domain proteins interactions. Our findings might increase the accuracy of cyclic peptide-protein conformational prediction, which may facilitate cyclic peptide inhibitor design. Our approach is expected to further aid in addressing the challenges in cyclic peptide inhibitor design.

Modulation of Protein Flexibility with Changes in Sequence and Complexation State of Ubiquitin Family Proteins

Ubiquitin (Ub) and small ubiquitin-related modifier (SUMO) proteins are structurally homologous molecular tags which regulate diverse cellular processes in eukaryotes. Here, we provide a conceptual basis to understand how nature harnesses protein flexibility, a molecular descriptor, to modulate the diversity of macromolecular interactions and cellular responses seen for ubiquitin family proteins. We hypothesize that the flexibility of ubiquitin family proteins is modulated by both changes in protein sequence and complexation with other proteins. To validate our hypothesis, we developed computational measures of protein flexibility, directional and overall spring constants, from microsecond molecular dynamics simulations and examined these measures for ubiquitin and SUMO proteins in free form and within complexes. Our results show ubiquitin to be stiffer than SUMO proteins and comparable stiffness for SUMO1 and SUMO2 proteins. Complexation with an E2 enzyme which attaches the ubiquitin tag (UBCH5A) to target proteins in the ubiquitylation cascade increases the intrinsic stiffness of ubiquitin. In contrast, complexation with a motif that recognizes ubiquitin tagged molecular cargo (TSG101 UEV domain) decreases intrinsic ubiquitin stiffness. Directional spring constants for ubiquitin (along N-C and 48-C directions), SUMO2 (N-C direction) and SUMO1 (N-C direction) show excellent correlations with spring constants extracted from single-molecule force spectroscopy pulling experiments and we provide experimentally testable predictions for stiffness in other directions. Our computational framework is transferable and can be applied to study subtle changes in protein flexibility as a function of sequence and complexation state in topologically similar proteins and structural motifs. Finally, our computational framework offers detailed insights on the nature of the underlying energy landscape sampled by proteins in molecular dynamics simulations.

The UBAP1 Subunit of ESCRT-I Interacts with Ubiquitin via a SOUBA Domain

SummaryThe endosomal sorting complexes required for transport (ESCRTs) facilitate endosomal sorting of ubiquitinated cargo, MVB biogenesis, late stages of cytokinesis, and retroviral budding. Here we show that ubiquitin associated protein 1 (UBAP1), a subunit of human ESCRT-I, coassembles in a stable 1:1:1:1 complex with Vps23/TSG101, VPS28, and VPS37. The X-ray crystal structure of the C-terminal region of UBAP1 reveals a domain that we describe as a solenoid of overlapping UBAs (SOUBA). NMR analysis shows that each of the three rigidly arranged overlapping UBAs making up the SOUBA interact with ubiquitin. We demonstrate that UBAP1-containing ESCRT-I is essential for degradation of antiviral cell-surface proteins, such as tetherin (BST-2/CD317), by viral countermeasures, namely, the HIV-1 accessory protein Vpu and the Kaposi sarcoma-associated herpesvirus (KSHV) ubiquitin ligase K5.

The Intrinsic Affinity between E2 and the Cys Domain of E1 in Ubiquitin-like Modifications

Ubiquitin-like modifications, which are carried out by similar biochemical mechanisms, regulate nearly every aspect of cellular function. Despite the recent advancements in characterizing their enzymology, our knowledge about the dynamic processes of these modifications is still fragmentary. In this study, we have uncovered an intrinsic affinity between the SUMO E2 and the Cys domain of SUMO E1. NMR studies in combination with paramagnetic spin labeling demonstrate that this interaction is mediated by previously unknown interfaces on both E1 and E2 and places the two catalytic Cys residues of the two enzymes in close proximity. Site-directed mutagenesis and enzymatic assays indicate that the interaction is fundamentally important for the transfer of SUMO from E1 to E2. Results from this study suggest that the interaction between E2 and the Cys domain of E1 participates in guiding the E2's translocation to E1's enzymatic active site in ubiquitin-like modifications.

Structure of human TSG101 UEV domain

The UEV domain of the TSG101 protein functions in the vacuolar protein-sorting pathway and in the budding process of HIV-1 and other retroviruses by recognizing ubiquitin in proteins tagged for degradation and short sequences in viral proteins containing an essential and well conserved PTAP motif, respectively. A deep understanding of these interactions is key to the rational design of much-needed novel antivirals. Here, the crystal structure of the TSG101 UEV domain (TSG101-UEV) is presented. TSG101-UEV was crystallized in the presence of PEG 4000 and ammonium sulfate. Under these conditions, crystals were obtained in space group R3, with unit-cell parameters a = b = 97.9, c = 110.6 A, alpha = beta = 90, gamma = 120 degrees . Phases were solved by molecular replacement and the crystal structure of TSG101-UEV was refined to an R factor of 18.8% at 2.2 A resolution. A comparison between the crystal structure and previously reported NMR structures has revealed significant differences in the conformation of one of the loops implicated in ubiquitin recognition. Also, the resulting structure has provided information about the presence of water molecules at the binding interface that could be of relevance for peptide recognition.

Ubiquitin Recognition by the Human TSG101 Protein

The UEV domain of the TSG101 protein functions in both HIV-1 budding and the vacuolar protein sorting (VPS) pathway, where it binds ubiquitylated proteins as they are sorted into vesicles that bud into late endosomal compartments called multivesicular bodies (MVBs). TSG101 UEV-ubiquitin interactions are therefore important for delivery of both substrates and hydrolytic enzymes to lysosomes, which receive proteins via fusion with MVBs. Here, we report the crystal structure of the TSG101 UEV domain in complex with ubiquitin at 2.0 Å resolution. TSG101 UEV contacts the Ile44 surface and an adjacent loop of ubiquitin through a highly solvated interface. Mutations that disrupt the interface inhibit MVB sorting, and the structure also explains how the TSG101 UEV can independently bind its ubiquitin and Pro-Thr/Ser-Ala-Pro peptide ligands. Remarkably, comparison with mapping data from other UEV and related E2 proteins indicates that although the different E2/UEV domains share the same structure and have conserved ubiquitin binding activity, they bind through very different interfaces.

Structure of the Tsg101 UEV Domain in Complex with a HIV-1 PTAP "Late Domain" Peptide

Structure of the Tsg101 UEV Domain in Complex with a HIV-1 PTAP "Late Domain" Peptide