Biology subjects

Koff, B. B.

Publications and source records attributed to Koff, B. B..

4 recordsLinked to original sources

bioRxiv2026

Extracellular HSPB1 protects intestinal epithelial cells against ethanol-activated ferroptosis

Alcohol consumption damages the gastrointestinal tract, the initial site of contact for ingested ethanol. Intestinal epithelial cells (IEC) lining the small intestine are at particular risk of ethanol toxicity since they are largely responsible for ethanol absorption and metabolize ethanol into toxic metabolites. These toxic metabolites generate oxidative stress that damages cellular components and leads to programmed cell death. The small heat shock protein HSPB1 regulates oxidative stress and provides cytoprotection in cells exposed to ethanol, but its specific role in intestinal ethanol toxicity is still unclear. Therefore, the goal of this study was to understand the role of HSPB1 in IEC stress response pathways during ethanol exposure. Here we utilized in vitro models to demonstrate that IEC rapidly upregulate and release HSPB1 in response to ethanol. HSPB1 expression in IEC mitigated oxidative stress, oxidative damage, and iron uptake, the hallmarks of ferroptosis, during ethanol stress. Interestingly, recombinant HSPB1 rescued cells, suggesting that extracellular HSPB1 is responsible for its protective effect. Our findings establish extracellular HSPB1 as a previously unrecognized mediator of IEC cytoprotection during acute ethanol exposure. However, HSPB1 functions as a "double-edged sword" along the gut-liver axis. While transient extracellular HSPB1 protects the gut epithelium from acute oxidative damage, sustained levels driven by chronic alcohol consumption lead to HSPB1 release from hepatocytes that activates macrophages and contributes to driving self-damaging inflammation in conditions like alcohol-associated hepatitis. Therefore, targeting extracellular HSPB1 levels along the gut-liver axis offers a promising diagnostic and therapeutic avenue to mitigate severe alcohol-induced organ injury.

pharmacology and toxicology↗

bioRxiv2024

Fluoride export is required for competitive fitness of pathogenic microorganisms in dental biofilm models

Microorganisms resist fluoride toxicity using fluoride export proteins from one of several different molecular families. Cariogenic species Streptococcus mutans and Candida albicans extrude intracellular fluoride using a CLCF F-/H+ antiporter and FEX fluoride channel, respectively, whereas commensal eubacteria, such as Streptococcus gordonii, export fluoride using a Fluc fluoride channel. In this work, we examine how genetic knockout of fluoride export impacts pathogen fitness in single-species and three-species dental biofilm models. For biofilms generated using S. mutans with genetic knockout of the CLCF transporter, exposure to low fluoride concentrations decreased S. mutans counts, synergistically reduced the populations of C. albicans, increased the relative proportion of commensal S. gordonii, and reduced properties associated with biofilm pathogenicity, including acid production and hydroxyapatite dissolution. Biofilms prepared with C. albicans with genetic knockout of the FEX channel also exhibited reduced fitness in the presence of fluoride, but to a lesser degree. Imaging studies indicate that S. mutans is highly sensitive to fluoride, with the knockout strain undergoing complete lysis when exposed to low fluoride for a moderate amount of time, and biochemical purification the S. mutans CLCF transporter and functional reconstitution establishes that the functional protein is a dimer encoded by a single gene. Together, these findings suggest that fluoride export by oral pathogens can be targeted by specific inhibitors to restore biofilm symbiosis in dental biofilms, and that S. mutans is especially susceptible to fluoride toxicity. ImportanceDental caries is a globally prevalent condition that occurs when pathogenic species, including Streptococcus mutans and Candida albicans, outcompete beneficial species, such as Streptococcus gordonii, in the dental biofilm. Fluoride is routinely used in oral hygiene to prevent dental caries. Fluoride also has antimicrobial properties, although most microbes possess fluoride exporters to resist its toxicity. This work shows that sensitization of cariogenic species Streptococcus mutans and Candida albicans to fluoride by genetic knockout of fluoride exporters alters the microbial composition and pathogenic properties of dental biofilms. These results suggest that the development of drugs that inhibit fluoride exporters could potentiate the anticaries effect of fluoride in over-the-counter products like toothpastes and mouth rinses. This is a novel strategy to treat dental caries.

microbiology↗

bioRxiv2022

Crystal structures of bacterial Small Multidrug Resistance transporter EmrE in complex with structurally diverse substrates

Proteins from the bacterial small multidrug resistance (SMR) family are proton-coupled exporters of diverse antiseptics and antimicrobials, including polyaromatic cations and quaternary ammonium compounds. The transport mechanism of the Escherichia coli transporter, EmrE, has been studied extensively, but a lack of high-resolution structural information has impeded a structural description of its molecular mechanism. Here we apply a novel approach, multipurpose crystallization chaperones, to solve several structures of EmrE, including a 2.9 [A] structure at low pH without substrate. We report five additional structures in complex with structurally diverse transported substrates, including quaternary phosphonium, quaternary ammonium, and planar polyaromatic compounds. These structures show that binding site tryptophan and glutamate residues adopt different rotamers to conform to disparate structures without requiring major rearrangements of the backbone structure. Structural and functional comparison to Gdx-Clo, an SMR protein that transports a much narrower spectrum of substrates, suggests that in EmrE, a relatively sparse hydrogen bond network among binding site residues permits increased sidechain flexibility.

biochemistry↗

bioRxiv2021

The fluoride permeation pathway and anion recognition in Fluc family fluoride channels

Fluc family fluoride channels protect microbes against ambient environmental fluoride by undermining the cytoplasmic accumulation of this toxic halide. These proteins are structurally idiosyncratic, and thus the permeation pathway and mechanism have no analogy in other known ion channels. Although fluoride binding sites were identified in previous structural studies, it was not evident how these ions access aqueous solution, and the molecular determinants of anion recognition and selectivity have not been elucidated. Using x-ray crystallography, planar bilayer electrophysiology and liposome-based assays, we identify additional binding sites along the permeation pathway. We use this information to develop an oriented system for planar lipid bilayer electrophysiology and observe anion block at one of these sites, revealing insights into the mechanism of anion recognition. We propose a permeation mechanism involving alternating occupancy of anion binding sites that are fully assembled only as the substrate approaches.

biochemistry↗