Protonation states of histidine and other key residues in deoxy normal human adult hemoglobin by neutron protein crystallography

A pH-sensitive motif in an outer membrane protein activates bacterial membrane vesicle production

Outer membrane vesicles (OMVs) produced by Gram-negative bacteria have key roles in cell envelope homeostasis, secretion, interbacterial communication, and pathogenesis. The facultative intracellular pathogen Salmonella Typhimurium increases OMV production inside the acidic vacuoles of host cells by changing expression of its outer membrane proteins and modifying the composition of lipid A. However, the molecular mechanisms that translate pH changes into OMV production are not completely understood. Here, we show that the outer membrane protein PagC promotes OMV production through pH-dependent interactions between its extracellular loops and surrounding lipopolysaccharide (LPS). Structural comparisons and mutational studies indicate that a pH-responsive amino acid motif in PagC extracellular loops, containing PagC-specific histidine residues, is crucial for OMV formation. Molecular dynamics simulations suggest that protonation of histidine residues leads to changes in the structure and flexibility of PagC extracellular loops and their interactions with the surrounding LPS, altering membrane curvature. Consistent with that hypothesis, mimicking acidic pH by mutating those histidine residues to lysine increases OMV production. Thus, our findings reveal a mechanism for sensing and responding to environmental pH and for control of membrane dynamics by outer membrane proteins.

The effects of standardized ileal digestible His to Lys ratio on growth performance, intestinal health, and mobilization of histidine-containing proteins in pigs at 7 to 11 kg body weight

The objectives were to evaluate the effects of standardized ileal digestible (SID) His:Lys ratio above the current NRC requirement on growth performance, intestinal health, and mobilization of His-containing proteins, including hemoglobin, carnosine, and trypsinogen, in nursery pigs from 7 to 11 kg body weight (BW). Forty pigs (26 d of age; initial BW of 7.1 ± 0.5 kg) were allotted to 5 dietary treatments based on a randomized complete block design with sex and initial BW as blocks. Dietary treatments were supplemented with varying SID His to Lys ratios of 26%, 32%, 38%, 43%, and 49% and fed to pigs for 14 d (SID Lys = 1.22%). Feed intake and BW were recorded at d 0, 7, and 14 to measure growth performance. Blood samples were collected on d 12. Pigs were euthanized on d 14 to collect pancreas, longissimus dorsi muscles, mid-jejunum, and jejunal mucosa. Data were analyzed using the Proc Mixed of SAS. Growth performance was not affected, whereas varying SID His to Lys ratio affected hemoglobin (P < 0.05, max: 12 g/dL at 36%), immunoglobulin A (IgA, P < 0.05, min: 1.25 μg/mg at 35%) in jejunal mucosa, villus height (P = 0.065, max: 536 μm at 40%) in jejunum, trypsinogen (P = 0.083, max: 242 pg/mg at 41%) in pancreas, and carnosine (P = 0.051, max: 4.7 ng/mg at 38%) in muscles. Varying SID His to Lys ratios linearly increased (P < 0.05, from 1.95 to 2.80 nmol/mg) protein carbonyl in muscles and decreased (P < 0.05, from 29.1% to 26.9%) enterocyte proliferation. In conclusion, SID His to Lys ratio between 35% and 41% in diets fed to nursery pigs at 7 to 11 kg enhanced intestinal health and maximized concentrations of His-containing proteins, indicating that His-containing proteins are effective response criteria when determining His requirement.

Detection of exogenous substances in latent fingermarks by silver-assisted LDI imaging MS: perspectives in forensic sciences

For over one hundred years, the fingerprint has reigned as one of the most trusted pieces of forensic evidence for suspect identification. Today, modern imaging mass spectrometry technology allows to correlate molecular information to the fingerprint giving us valuable insights into a suspect lifestyle and behaviour.

AltitudeOmics: Red Blood Cell Metabolic Adaptation to High Altitude Hypoxia

Red blood cells (RBCs) are key players in systemic oxygen transport. RBCs respond to in vitro hypoxia through the so-called oxygen-dependent metabolic regulation, which involves the competitive binding of deoxyhemoglobin and glycolytic enzymes to the N-terminal cytosolic domain of band 3. This mechanism promotes the accumulation of 2,3-DPG, stabilizing the deoxygenated state of hemoglobin, and cytosol acidification, triggering oxygen off-loading through the Bohr effect. Despite in vitro studies, in vivo adaptations to hypoxia have not yet been completely elucidated. Within the framework of the AltitudeOmics study, erythrocytes were collected from 21 healthy volunteers at sea level, after exposure to high altitude (5260 m) for 1, 7, and 16 days, and following reascent after 7 days at 1525 m. UHPLC-MS metabolomics results were correlated to physiological and athletic performance parameters. Immediate metabolic adaptations were noted as early as a few hours from ascending to >5000 m, and maintained for 16 days at high altitude. Consistent with the mechanisms elucidated in vitro, hypoxia promoted glycolysis and deregulated the pentose phosphate pathway, as well purine catabolism, glutathione homeostasis, arginine/nitric oxide, and sulfur/H₂S metabolism. Metabolic adaptations were preserved 1 week after descent, consistently with improved physical performances in comparison to the first ascendance, suggesting a mechanism of metabolic memory.