Biology subjects

Jonker, T.

Publications and source records attributed to Jonker, T..

3 recordsLinked to original sources

bioRxiv2025

Characterization of the Mitomycin C Resistance Protein McrA

McrA from Streptomyces lavendulae is a flavin-dependent enzyme thought to provide self-resistance against the DNA-alkylating antibiotic mitomycin C (MMC). McrA belongs to the berberine bridge enzyme (BBE)-like subfamily of oxidases and catalyzes the oxidation of reduced MMC converting it back into the inactive prodrug form, thereby preventing rearrangement into the reactive quinone methide intermediate. Here we demonstrate the first crystal structure of McrA, allowing us to identify key residues involved in retaining MMC in the active site. Biochemical characterization studies such as pre-steady state kinetics verified McrA oxidase activity, while binding studies demonstrated its ability to recognize oxidized MMC.

biochemistry↗

bioRxiv2025

AAV6-HCN4t-mediated biological pacing as a potential life-saving therapy for congenital complete heart block

Congenital complete heart block (CCHB) is a life-threatening condition in fetuses due to severe bradycardia. Maternal administration of {beta}-adrenergic agonists is used to increase fetal heart rates, but its effectiveness is limited and lost over time most likely due to insufficient expression of HCN channels in some individuals. We report the development of an injectable gene therapy that produces reliable cardiac pacemaker function in the presence of {beta}-adrenergic stimulation. Intramyocardial injection of adeno-associated viral serotype 6 vectors expressing HCN4t (AAV6-HCN4t) into the left ventricular apex significantly increased ectopic pacing frequency and heart rate in response to isoproterenol in rats with complete heart block, and this effect remained stable throughout the 4 weeks of follow-up. Injection of AAV6-HCN4t showed similar reliable biological pacing in complete heart block pigs. These results suggest that AAV6-HCN4t generates robust biological pacing in the presence of isoproterenol, providing the foundation for a potentially life-saving therapy for in utero CCHB.

physiology↗

bioRxiv2024

Membrane fusion-based drug delivery liposomes transiently modify the material properties of synthetic and biological membranes

Many drug targets are located in intracellular compartments of cells but they often remain inaccessible to standard imaging and therapeutic agents. To aid intracellular delivery, drug carrier nanoparticles have been used to overcome the barrier imposed by the plasma membrane. The carrier must entrap large amounts of cargo, efficiently and quickly deliver the cargo in the cytosol or other intracellular compartments, and must be as inert as possible. In other words, they should not induce cellular responses or alter the cell state in the course of delivery. Here, we show that cationic liposomes with high charge density efficiently fuse with synthetic membranes and the plasma membrane of living cells. Direct fusion efficiently delivers large amounts of cargo to cells and cell-like vesicles within seconds, bypassing slow and often inefficient internalization-based pathways. These effects depend on liposome charge density and, to some extent, liposome concentration and the helper lipid. However, fusion-mediated cargo delivery results in the incorporation of large amounts of foreign lipids that leads to changes in the material properties of these membranes, namely modifications in membrane packing and fluidity, induction of membrane curvature, decrease in surface tension and the formation of (short-lived) pores. Importantly, these effects are transient and liposome removal allows cells to recover their state prior to liposome interaction.

biophysics↗