Biology subjects

Belvin, B. R.

Publications and source records attributed to Belvin, B. R..

5 recordsLinked to original sources

bioRxiv2026

Nitrate-Reducing Commensals Reshape Oral Biofilm Ecology and Reveal Hcp as a Critical Determinant of Porphyromonas gingivalis Persistence

Dietary nitrate (NO-) supplementation is emerging as a promising strategy for suppressing oral pathobionts through microbial generation of reactive nitrogen species (RNS), including nitrite (NO2-) and nitric oxide (NO). However, the mechanisms that enable periodontal pathogens to survive nitrate-derived nitrosative stress within polymicrobial communities remain poorly understood. Previously, we identified the hybrid cluster protein (Hcp) as a major nitrosative stress defense factor in Porphyromonas gingivalis demonstrating [~]170-fold induction of hcp expression following nitrite exposure and as a requirement for survival at physiologically relevant nitrite concentrations. Here we investigated the role of Hcp in promoting P. gingivalis persistence within nitrate-reducing biofilms. Using human ex vivo plaque biofilms, we found that Hcp is essential for P. gingivalis survival under both basal and nitrate-supplemented conditions. In a defined nine-species biofilm model, nitrate reduction suppressed wild-type P. gingivalis, whereas deletion of hcp ({Delta}hcp) resulted in complete population clearance. Metatranscriptomics revealed that nitrate-induced hcp expression was not restricted to P. gingivalis but was part of a coordinated nitrosative stress response shared among oral anaerobes, including Prevotella intermedia, Fusobacterium nucleatum, and Veillonella atypica. Moreover, nitrate reduction disrupted a previously synergistic interaction between Veillonella spp. and P. gingivalis, converting a supportive relationship into an inhibitory microenvironment that constrained pathogen survival. Collectively, these findings identify Hcp-mediated nitrosative stress resistance as a major determinant of fitness within nitrate-reducing biofilms and reveal RNS as key ecological force shaping interactions between commensal nitrate reducers and periodontal pathogens. These results provide a mechanistic framework linking dietary nitrate metabolism to oral microbiome homeostasis.

microbiology↗

bioRxiv2025

Identification and characterization of Porphyromonas gingivalis TonB

Porphyromonas gingivalis is one of the major bacterial pathogens responsible for the initiation and progression of periodontal disease. The bacterium codes for multiple TonB-dependent receptors required for acquisition of nutrients such as heme and vitamin B12, although the identity of a TonB energy transducer has yet to be identified. Here we identify a potential TonB protein encoded by PG0785, generate a deficient strain, and characterize its biological significance. Bioinformatics analysis reveals that the PG0785 has unique features confined to the Cytophaga-Flavobacterium-Bacteroides (CFB) group of bacteria but shares similarities in the C-terminal domain (CTD) to well characterized proteins from Helicobacter pylori and Escherichia coli. Similarity at a protein level, as well as the genomic locus organization, was identified with the TonB proteins characterized in other Bacteroidota species. Loss of PG0785 led to significant alteration of the proteome: proteins mediating gene regulation, protein translation, protection against reactive radical species (oxygen and nitrogen), and glycosylation were up-regulated and polysaccharide export, efflux protein, and lipoproteins were downregulated. Furthermore, phenotypic studies showed that a mutant lacking PG0785 cannot accumulate heme on its surface and is deficient in gingipain protease activity. In addition, reduction of the capsular layer was detected in the TonB-deficient strain. Thus, while the mutant interacted and invaded eukaryotic cells at much higher levels than the wild type, it had significantly reduced ability to survive with host cells. ImportanceThe TonB system is indispensable for energy transduction in Gram-negative bacteria and is mainly associated with nutrient uptake. Although well investigated in Proteobacteria, the knowledge regarding the system in the CFB group of bacteria is lagging. In contrast to Proteobacteria, the intestinal Bacteroidota have multiple TonBs and their novel involvement in sugar utilization has been demonstrated. This study shows that the oral Bacteroidota, Porphyromonas gingivalis, also has TonB but unexpectedly, it is not involved in iron homeostasis or nutrient acquisition but rather in processes involved in maturation of proteases and cell surface remodeling. As maintenance of outer membrane integrity is mainly associated with Tol motor our study shows possible crosstalk between the energy transducers. Also, this study further demonstrates the functional versatility of the TonB system depending on the environmental niche and the metabolic requirements of the bacteria.

microbiology↗

bioRxiv2024

Full-length structure and heme binding in the transcriptional regulator HcpR

HcpR is a CRP-family transcriptional regulator found in many Gram-negative anaerobic bacteria. In the perio-pathogen Porphyromonas gingivalis, HcpR is crucial for the response to reactive nitrogen species such as nitric oxide (NO). Binding of NO to the heme group of HcpR leads to transcription of the redox enzyme Hcp. However, the molecular mechanisms of heme binding to HcpR remain unknown. In this study we present the 2.3[A] structure of the P. gingivalis HcpR. Interdomain interactions present in the structure help to form a hydrophobic pocket in the N-terminal sensing domain. A comparison analysis with other CRP-family members reveals that the molecular mechanisms of HcpR-mediated regulation may be distinct from other family members. Using docking studies, we identify a putative heme binding site in the sensing domain. In vitro complementation and mutagenesis studies verify Met68 as an important residue in activation of HcpR. Finally, heme binding studies with purified forms of recombinant HcpR support Met68 and His149 residues as important for proper heme coordination in HcpR.

microbiology↗

bioRxiv2024

Targeting of SUMOylation leads to cBAF complex stabilization and disruption of the SS18::SSX transcriptome in Synovial Sarcoma

Synovial Sarcoma (SS) is driven by the SS18::SSX fusion oncoprotein. and is ultimately refractory to therapeutic approaches. SS18::SSX alters ATP-dependent chromatin remodeling BAF (mammalian SWI/SNF) complexes, leading to the degradation of canonical (cBAF) complex and amplified presence of an SS18::SSX-containing non-canonical BAF (ncBAF or GBAF) that drives an SS-specific transcription program and tumorigenesis. We demonstrate that SS18::SSX activates the SUMOylation program and SSs are sensitive to the small molecule SAE1/2 inhibitor, TAK-981. Mechanistically, TAK-981 de-SUMOylates the cBAF subunit SMARCE1, stabilizing and restoring cBAF on chromatin, shifting away from SS18::SSX-ncBAF-driven transcription, associated with DNA damage and cell death and resulting in tumor inhibition across both human and mouse SS tumor models. TAK-981 synergized with cytotoxic chemotherapy through increased DNA damage, leading to tumor regression. Targeting the SUMOylation pathway in SS restores cBAF complexes and blocks the SS18::SSX-ncBAF transcriptome, identifying a therapeutic vulnerability in SS, positioning the in-clinic TAK-981 to treat SS.

cancer biology↗

bioRxiv2022

Ferroportin Depletes Iron Needed for Cell Cycle Progression in Head and Neck Squamous Cell Carcinoma

Ferroportin (FPN), the only identified eukaryotic iron efflux channel, plays an important role in iron homeostasis and is down regulated in many cancers. To determine if iron related pathways are important for HNSCC progression and proliferation, we utilize a model of FPN over-expression to simulate iron depletion and probe associated molecular pathways. HNSCC cells are sensitive to iron chelation and ferroptosis, but a non-transformed normal oral keratinocyte (NOK) cell line is not. We found that FPN expression inhibits HNSCC cell proliferation and colony formation but NOK cells are unaffected. Inhibition of cell proliferation is rescued by the addition hepcidin. Decreases in proliferation are due to the disruption of iron homeostasis via loss of labile iron caused by elevated FPN levels. This in turn protects HNSCC cells from ferroptotic cell death. Expression of FPN induces DNA damage, activates p21 and reduces mRNA levels of cyclin proteins thereby inhibiting cell cycle progression of HNSCC cells, arresting cells in S-phase. Induction of FPN severely inhibits Edu incorporation and increases {beta}-galactosidase activity, indicating cells have entered senescence. Finally, in an oral orthotopic mouse xenograft model, FPN induction yields a decrease of tumor growth. Our results indicate that iron plays a role in HNSCC cell proliferation and sustained growth and ferroptosis iron based therapeutic strategies may have potential therapeutic benefit.

cancer biology↗