An Intracellular Pathway Controlled by the N-terminus of the Pump Subunit Inhibits the Bacterial KdpFABC Ion Pump in High K+ Conditions

Transcriptome responses of Lactococcus paracarnosus to different gas compositions and co-culture with Brochothrix thermosphacta

Lactococcus (Lc.) paracarnosus and the phylogenetically closely related Lc. carnosus species are common members of the microbiota in meat stored under modified atmosphere and at low temperature. The effect of these strains on meat spoilage is controversially discussed. While some strains are known to cause spoilage, others are being studied for their potential to suppress the growth of spoilage and pathogenic bacteria. In this study, Lc. paracarnosus DSM 111017T was selected based on a previous study for its ability to suppress the growth of meat spoilers, including Brochothrix thermosphacta. The mechanism by which this bioprotective strain inhibits competing bacteria and how it contributes to spoilage are not yet known. To answer these two questions, we investigated the effect of four different headspace gas mixtures (simulated air (21 % O2/79 % N2); HiOx-MAP (70 % O2/30 % CO2); nonOx-MAP (70 % N2/ 30 % CO2); simulated vacuum (100 % N2) and the presence of Brochothrix (B.) thermosphacta TMW 2.2101 on the growth and transcriptional response of Lc. paracarnosus DSM 111017T when cultured on a meat simulation agar surface at 4 °C. Analysis of genes specifically upregulated by the gas mixtures used revealed metabolic pathways that may lead to different levels of spoilage metabolites production. We propose that under elevated oxygen levels, Lc. paracarnosus preferentially converts pyruvate from glucose and glycerol to uncharged acetoin/diacetyl instead of lactate to counteract acid stress. Due to the potential production of a buttery off-flavour, the strain may not be suitable as a protective culture in meat packaged under high‑oxygen conditions. 70 % N2/ 30 % CO2, simulated vacuum- and the presence of Lc. paracarnosus inhibited the growth of B. thermosphacta TMW 2.2101. However, B. thermosphacta did not affect gene regulation of metabolic pathways in Lc. paracarnosus, and genes previously predicted to be involved in B. thermosphacta growth suppression were not regulated at the transcriptional level. In conclusion, the study indicates that the gas mixture used in packaging significantly affects the metabolism and spoilage potential of Lc. paracarnosus and its ability to inhibit B. thermosphacta growth.

Structural Basis for Binding of Potassium-Competitive Acid Blockers to the Gastric Proton Pump

As specific inhibitors of the gastric proton pump, responsible for gastric acidification, K⁺-competitive acid blockers (P-CABs) have recently been utilized in the clinical treatment of gastric acid-related diseases in Asia. However, as these compounds have been developed based on phenotypic screening, their detailed binding poses are unknown. We show crystal and cryo-EM structures of the gastric proton pump in complex with four different P-CABs, tegoprazan, soraprazan, PF-03716556 and revaprazan, at resolutions reaching 2.8 Å. The structures describe molecular details of their interactions and are supported by functional analyses of mutations and molecular dynamics simulations. We reveal that revaprazan has a novel binding mode in which its tetrahydroisoquinoline moiety binds deep in the cation transport conduit. The mechanism of action of these P-CABs can now be evaluated at the molecular level, which will facilitate the rational development and improvement of currently available P-CABs to provide better treatment of acid-related gastrointestinal diseases.