Vacuolar proton-translocating ATPase pumps consist of two domains, V 1 and V o . Subunit d is a component of V o located in a central stalk that rotates during catalysis. By generating mutations, we showed that subunit d couples ATP hydrolysis and proton transport. The mutation F94A strongly uncoupled the enzyme, preventing proton transport but not ATPase activity. C-terminal mutations changed coupling as well; ATPase activity was decreased by 59 -72%, whereas proton transport was not measurable (E328A) or was moderately reduced (E317A and C329A). Except for W325A, which had low levels of V 1 V o , mutations allowed wild-type assembly regardless of the fact that subunits E and d were reduced at the membrane. N-and C-terminal deletions of various lengths were inhibitory and gradually desta- Viral infections, cancer, osteoporosis, and renal tubular acidosis are some of the human disease states associated with the V-ATPase 2 function. V-ATPases are ATP-driven proton pumps present in Golgi, endosomes, lysosomes, and vacuoles, where they are responsible for maintaining the acidic luminal pH essential for receptor-mediated endocytosis, zymogen activation, and protein sorting (1-4). In addition to the endogenously distributed V-ATPases, some cells contain V-ATPases at the plasma membrane, where they pump protons from the cytosol to the extracellular milieu. V-ATPase proton transport across the plasma membrane is essential for bone resorption, urinary acidification, sperm maturation, and neurotransmitter sequestration (3).V-ATPases are related to F-ATP synthases (5), and both protein complexes work as molecular motors (6 -9). V-ATPases, however, work exclusively in the direction of ATP hydrolysis in vivo. V-ATPases consist of two domains, V 1 and V o , similar to the F 1 and F o domains found in ATP synthases (1-4). Eight different subunits (A-H) compose V 1 , which is peripherally attached to the membrane and hydrolyzes ATP (1-4). Six different subunits (a, c, cЈ, cЉ, d, and e) associate to form V o , which holds V 1 at the membrane and forms the path to transport protons (1-4). V 1 and V o subunits contribute to the formation of one central stalk and two or three peripheral stalk structures that connect a proteolipid ring (made of subunits c, cЈ, and cЉ) in V o and the catalytic core of V 1 (a hexamer of three subunits A alternating with three subunits B) (10, 11).The organization of the central and peripheral stalks is essential for structural and functional coupling of ATP hydrolysis and proton transport. It is proposed that during catalysis, ATP hydrolysis at the V 1 hexamer A 3 B 3 drives rotation of a rotor (central stalk made of subunits D, F, and d connected to the proteolipid ring) (6, 12). Six essential glutamates are protonated in the ring when protons are transferred from the cytosol via two half-tunnel structures formed in the stationary subunit a at the membrane (13-15). By connecting the stationary subunits (A 3 B 3 and a), the peripheral stalk(s) (subunits C, E, G, H, and the N terminus of subunit a) wo...

Rechargeable magnesium batteries provide the potential for lower cost and improved safety compared with lithium-ion batteries, however obtaining cathode materials with highly reversible Mg-ion capacities is hindered by the high polarizability of divalent Mg-ions and slow solid-state Mg-ion diffusion. We report that incorporating poly(ethylene oxide) (PEO) between the layers of hydrated vanadium pentoxide (V 2 O 5) xerogels results in significantly improved reversible Mg-ion capacities. X-ray diffraction and high resolution transmission electron microscopy show that the interlayer spacing between V 2 O 5 layers was increased by PEO incorporation. Vibrational spectroscopy supports that the polymer interacts with the V 2 O 5 lattice. The V 2 O 5-PEO nanocomposite exhibited a 5-fold enhancement in Mg-ion capacity, improved stability, and improved rate capabilities compared with V 2 O 5 xerogels. The Mg-ion diffusion coefficient of the nanocomposite was increased compared with that of V 2 O 5 xerogels and is attributed to enhanced Mg-ion mobility due to shielding interaction of PEO with the V 2 O 5 lattice. This study shows that beyond only interlayer spacing, the nature of interlayer interactions of Mg-ions with V 2 O 5 , PEO, and H 2 O are key factors that affect Mg-ion charge transport and storage in layered materials. The design of layered materials with controlled interlayer interactions provides a new approach to develop improved cathodes for magnesium batteries.

Acidic oxygen evolution reaction (OER) electrocatalysts that have high activity, extended durability, and lower costs are needed to further the development and wide-scale adoption of proton-exchange membrane electrolyzers. In this...