Electrochemically induced deposition of poly(benzoxazine) precursors as immobilization matrix for enzymes

Pyrroloquinoline quinone-dependent glucose dehydrogenase bioelectrodes based on one-step electrochemical entrapment over single-wall carbon nanotubes

Development of effective direct electron transfer is considered an interesting platform to obtain high performance bioelectrodes. Therefore, designing of scalable and cost-effective immobilization routes that promotes correct direct electrical contacting between the electrode material and the redox enzyme is still required. As we present here, electrochemical entrapment of pyrroloquinoline quinone-dependent glucose dehydrogenase (PQQ-GDH) on single-wall carbon nanotube (SWCNT)-modified electrodes was carried out in a single step during electrooxidation of para-aminophenyl phosphonic acid (4-APPA) to obtain active bioelectrodes. The adequate interaction between SWCNTs and the enzyme can be achieved by making use of phosphorus groups introduced during the electrochemical co-deposition of films, improving the electrocatalytic activity towards glucose oxidation. Two different procedures were investigated for electrode fabrication, namely the entrapment of reconstituted holoenzyme (PQQ-GDH) and the entrapment of apoenzyme (apo-GDH) followed by subsequent in situ reconstitution with the redox cofactor PQQ. In both cases, PQQ-GDH preserves its electrocatalytic activity towards glucose oxidation. Moreover, in comparison with a conventional drop-casting method, an important enhancement in sensitivity was obtained for glucose oxidation (981.7 ± 3.5 nA mM^-1) using substantially lower amounts of enzyme and cofactor (PQQ). The single step electrochemical entrapment in presence of 4-APPA provides a simple method for the fabrication of enzymatic bioelectrodes.

Mechanical stretch activates piezo1 in caveolae of alveolar type I cells to trigger ATP release and paracrine stimulation of surfactant secretion from alveolar type II cells

Secretion of pulmonary surfactant in the alveoli of the lungs is essential to maintain lung function. Stretching of alveoli during lung inflation is the main trigger for surfactant secretion. Yet, the molecular mechanisms how mechanical distension of alveoli results in surfactant secretion are still elusive. The alveolar epithelium consists of alveolar epithelial type I (ATI) and surfactant secreting type II (ATII) cells. ATI, but not ATII cells, express caveolae, small plasma membrane invaginations that can respond to plasma membrane stresses and serve mechanotransductive roles. Within this study, we investigated the role of caveolae as mechanosensors in the alveolus. We generated a human caveolin-1 knockout ATI cell (hAELVi^cav-/- ) using CRISPR/Cas9. Wildtype (hAELVi^wt ) and hAELVi^cav-/- cells grown on flexible membranes responded to increasing stretch amplitudes with rises in intracellular Ca²⁺ . The response was less frequent and started at higher stretch amplitudes in hAELVi^cav-/- cells. Stretch-induced Ca²⁺ -signals depended on Ca²⁺ -entry via piezo1 channels, localized within caveolae in hAELVi^wt and primary ATI cells. Ca²⁺ -entry via piezo1 activated pannexin-1 hemichannels resulting in ATP release from ATI cells. ATP release was reduced in hAELVi^cav-/- cells. In co-cultures resembling the alveolar epithelium, released ATP stimulated Ca²⁺ signals and surfactant secretion from neighboring ATII cells when co-cultured with hAELVi^wt but not hAELVi^cav-/- cells. In summary, we propose that caveolae in ATI cells are mechanosensors within alveoli regulating stretch-induced surfactant secretion from ATII cells.

(Multi)functional Atomic Force Microscopy Imaging

Incorporating functionality to atomic force microscopy (AFM) to obtain physical and chemical information has always been a strong focus in AFM research. Modifying AFM probes with specific molecules permits accessibility of chemical information via specific reactions and interactions. Fundamental understanding of molecular processes at the solid/liquid interface with high spatial resolution is essential to many emerging research areas. Nanoscale electrochemical imaging has emerged as a complementary technique to advanced AFM techniques, providing information on electrochemical interfacial processes. While this review presents a brief introduction to advanced AFM imaging modes, such as multiparametric AFM and topography recognition imaging, the main focus herein is on electrochemical imaging via hybrid AFM-scanning electrochemical microscopy. Recent applications and the challenges associated with such nanoelectrochemical imaging strategies are presented.

ATP is stored in lamellar bodies to activate vesicular P2X4 in an autocrine fashion upon exocytosis

P2X₄ receptor activation facilitates secretion of pulmonary surfactant from secretory vesicles called lamellar bodies in alveolar epithelial cells. Fois et al. reveal that P2X₄ receptors on the lamellar body membranes are activated by ATP stored within the vesicles themselves upon vesicle exocytosis.

Vesicular P2X₄ receptors are known to facilitate secretion and activation of pulmonary surfactant in the alveoli of the lungs. P2X₄ receptors are expressed in the membrane of lamellar bodies (LBs), large secretory lysosomes that store lung surfactant in alveolar type II epithelial cells, and become inserted into the plasma membrane after exocytosis. Subsequent activation of P2X₄ receptors by adenosine triphosphate (ATP) results in local fusion-activated cation entry (FACE), facilitating fusion pore dilation, surfactant secretion, and surfactant activation. Despite the importance of ATP in the alveoli, and hence lung function, the origin of ATP in the alveoli is still elusive. In this study, we demonstrate that ATP is stored within LBs themselves at a concentration of ∼1.9 mM. ATP is loaded into LBs by the vesicular nucleotide transporter but does not activate P2X₄ receptors because of the low intraluminal pH (5.5). However, the rise in intravesicular pH after opening of the exocytic fusion pore results in immediate activation of vesicular P2X₄ by vesicular ATP. Our data suggest a new model in which agonist (ATP) and receptor (P2X₄) are located in the same intracellular compartment (LB), protected from premature degradation (ATP) and activation (P2X₄), and ideally placed to ensure coordinated and timely receptor activation as soon as fusion occurs to facilitate surfactant secretion.

Poly(benzoxazine)s Modified with Osmium Complexes as a Class of Redox Polymers for Wiring of Enzymes to Electrode Surfaces

Benzoxazine-based redox polymers bearing Os complexes are synthesized and used as an immobilization matrix for glucose oxidase (GOx) as a model system for a reagentless biosensor. The polymers are formed by electrochemically induced anodic polymerization of the corresponding benzoxazine monomers modified with Os complexes. The precursors are synthesized in a Mannich-type reaction between bisphenol A, formaldehyde, and the corresponding Os complexes or ligands, which contain free amino groups. The Os complexes are redox active within the polymer films, and thus, can be used as redox relays for the electron transfer between the electrode surface and the prosthetic group within the enzyme. Entrapment of GOx within the poly(benzoxazine) film is achieved successfully, as shown by the biocatalytic activity of the poly(benzoxazine)/GOx films upon the addition of glucose.