Our lab investigates the anti-HIV-1 activity in Momordica balsamina (M. balsamina) leaf extract. Traditional Senegalese healers have used M. balsamina leaf extract as a part of a plant-based treatment for HIV/AIDS infections. Our overall goal is to define and validate the scientific basis for using M. balsamina leaf extract as a part of the traditional Senegalese treatment. As an initial characterization of this extract, we used activity-guided fractionation to determine the active ingredient’s solubility and relative size. We found that M. balsamina leaf extract inhibits HIV-1 infection by >50% at concentrations of 0.02 mg/mL and above and is not toxic over its inhibitory range (0–0.5 mg/mL). We observed significantly more antiviral activity in direct water and acetonitrile extractions (p ≤ 0.05). We also observed significantly more antiviral activity in the aqueous phases of ethyl acetate, chloroform, and diethyl ether extractions (p ≤ 0.05). Though most of the antiviral activity partitioned into the aqueous layers, some antiviral activity was present in the organic layers. We show that the active agent in the plant extracts is at least 30 kD in size. Significantly more antiviral activity was retained in 3, 10, and 30 kD molecular weight cutoff filters (p ≤ 0.05). In contrast, most of the antiviral activity passed through the 100 kD filter (p ≤ 0.05). Because the active anti-HIV-1 agent presented as a large, amphiphilic molecule we ran the purified extract on an SDS-page gel. We show that the anti-HIV-1 activity in the leaf extracts is attributed to a 30 kDa protein we call MoMo30. This article describes how MoMo30 was determined to be responsible for its anti-HIV-1 activity.

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.

The HECT domain of HECT E3 ligases consists of flexibly linked N- and C-terminal lobes, with a ubiquitin (Ub) donor site on the C-lobe that is directly involved in substrate modification. HECT ligases also possess a secondary Ub binding site in the N-lobe, which is thought to play a role in processivity, specificity, or regulation. Here, we report the use of paramagnetic solution NMR to characterize a complex formed between the isolated HECT domain of neural precursor cell-expressed developmentally downregulated 4-1 and the ubiquitin E2 variant (UEV) domain of tumor susceptibility gene 101 (Tsg101). Both proteins are involved in endosomal trafficking, a process driven by Ub signaling, and are hijacked by viral pathogens for particle assembly; however, a direct interaction between them has not been described, and the mechanism by which the HECT E3 ligase contributes to pathogen formation has not been elucidated. We provide evidence for their association, consisting of multiple sites on the neural precursor cell-expressed developmentally downregulated 4-1 HECT domain and elements of the Tsg101 UEV domain involved in noncovalent ubiquitin binding. Furthermore, we show using an established reporter assay that HECT residues perturbed by UEV proximity define determinants of viral maturation and infectivity. These results suggest the UEV interaction is a determinant of HECT activity in Ub signaling. As the endosomal trafficking pathway is hijacked by several human pathogens for egress, the HECT-UEV interaction could represent a potential novel target for therapeutic intervention.

MoMo30 is an antiviral protein isolated from aqueous extracts of Momordica balsamina L. (Senegalese bitter melon). Previously, we demonstrated MoMo30’s antiviral activity against HIV-1. Here, we explore whether MoMo30 has antiviral activity against the COVID-19 virus, SARS-CoV-2. MLV particles pseudotyped with the SARS-CoV-2 Spike glycoprotein and a Luciferase reporter gene (SARS2-PsV) were developed from a three-way co-transfection of HEK293-T17 cells. MoMo30’s inhibition of SARS2-PsV infection was measured using a luciferase assay and its cytotoxicity using an XTT assay. Additionally, MoMo30’s interactions with the variants and domains of Spike were determined by ELISA. We show that MoMo30 inhibits SARS2-PsV infection. We also report evidence of the direct interaction of MoMo30 and SARS-CoV-2 Spike from WH-1, Alpha, Delta, and Omicron variants. Furthermore, MoMo30 interacts with both the S1 and S2 domains of Spike but not the receptor binding domain (RBD), suggesting that MoMo30 inhibits SARS-CoV-2 infection by inhibiting fusion of the virus and the host cell via interactions with Spike.

Breast cancer (BC) is a major cause of cancer-related mortality. Mortalin and Vimentin—two proteins implicated in BC progression and metastasis—have been identified as binding partners of the Secretion Modification Region (SMR) peptide from the HIV Nef protein. These interactions disrupt exosome release and offer novel therapeutic strategies. This study investigates the binding interactions between the SMR peptide, Mortalin, and Vimentin using surface plasmon resonance (SPR), co-immunoprecipitation (Co-IP), and Western blot assays. We also map the SMR binding sites on Mortalin through scanning peptide mapping and then identify a similar site on the Vimentin protein. Based on these data, we propose that the SMR peptide and its analogs interact with specific amino acid sequences in Mortalin and Vimentin, thereby disrupting cellular processes essential for Epithelial–Mesenchymal Transition (EMT) and tumor progression. SPR analysis revealed that the Nef protein exhibited the highest binding affinity to Vimentin (KD = 0.75 ± 1.1 nM) and Mortalin (KD = 3.16 ± 0.03 nM). The SMRwt peptide also demonstrated direct binding to both proteins with micromolar affinities (KD = 6.63 ± 0.74 µM for Vimentin; KD = 20.73 ± 2.33 µM for Mortalin), though the binding affinity was weaker than the full Nef protein. Co-IP experiments using MDA-MB-231, MCF-7, and BT474 BC cell lines confirmed that SMRwt, but not SMRmut, co-immunoprecipitated with Mortalin. Western blot analysis validated these interactions. Further, Mortalin peptide #56, derived from the substrate-binding domain, did not bind the SMR domain or inhibit Nef function. In contrast, peptides #61 and #62 from the C-terminal domain of Mortalin bound the SMR domain and effectively inhibited Nef activity. Notably, Mortalin peptide #61 inhibited SMRwt binding to both Mortalin and Vimentin, disrupting complex formation on the SPR sensor chip. These findings suggest that specific Mortalin-derived peptides can block SMR interactions, offering a potential therapeutic mechanism.

Momordica balsamina, a plant traditionally used in African medicine, contains a 30 kDa protein, MoMo30, previously identified by our group as an anti-HIV agent that binds glycan residues on the gp120 envelope protein, thereby acting as an entry inhibitor. In this study, we investigated whether prolonged exposure to MoMo30 exerts selective pressure on HIV-1 and induces mutations in the viral envelope (env) gene. T-lymphocyte cells were infected with HIV-1_NL4-3 and continuously treated with MoMo30 over a 24-day period. Viral RNA was isolated at regular intervals, and env genes were sequenced using the Illumina platform. RNA sequence variant calling was performed using iVar, which uses a frequency-based binomial test with a default allele frequency threshold of 3% and a minimum base quality of 20 and applies Bonferroni correction for multiple testing. The infectivity of the MoMo30-exposed virus was assessed using MAGI-CXCR4 cells, visualized by β-galactosidase staining, and compared to untreated controls. Statistical significance was determined via two-way ANOVA. MoMo30-treated HIV-1 exhibited multiple detrimental mutations in gp120 and gp41, including missense, nonsense, and frameshift changes. Notably, 32% of N-linked glycosylation sites were deleted in the treated virus, while no such changes were observed in controls. Functionally, the MoMo30-treated virus demonstrated a sixfold reduction in infectivity compared to untreated HIV-1_NL4-3. These findings suggest that MoMo30 imposes genetic pressure on HIV-1_NL4-3, selecting for mutations that reduce viral fitness.