Spectroscopical identification of residues of subunit G of the yeast V-ATPase in its connection with subunit E

Response of the vacuolar ATPase subunit E to RNA interference and four chemical pesticides in Leptinotarsa decemlineata (Say)

Vacuolar-type H(+)-ATPases (vATPases) are localized in the apical membranes of nearly all epithelial tissues of insects, energize the membranes to absorb and/or secrete ions and fluids, and play essential roles in many physiological functions. Here we cloned and characterized a 1041-bp full-length vATPase subunit E cDNA (named as LdATPaseE) that encoded a 226-amino acid protein in Leptinotarsa decemlineata. LdATPaseE mRNA levels were constantly increased from egg to the third- and fourth-instar stages, dropped in wandering and pupal stages and were elevated again in the adult stage. It was highly expressed in ileum and rectum, moderately expressed in Malpighian tubules, midgut and foregut, and lowly expressed in fat body, ventral ganglion, epidermis and haemocytes in the fourth instars. After continuously ingested double-stranded RNAs originated from two LdATPaseE fragments LdATPaseE1 and LdATPaseE2, the target mRNA levels in the larvae were reduced by 85% and 55%, the larval growth and survival were significantly affected. Furthermore, topical application of fipronil, butane-fipronil, endosulfan and cypermethrin significantly upregulated LdATPaseE expression up to 8.3, 4.2, 2.8 and 6.2-fold 1 day after experiment, and up to 15.8, 3.4, 3.6 and 4.5-fold 2 days after treatment. It seems that depletion of vATPase subunit E is lethal, indicating that targeting vATPases by dsRNA appears a promising means of combating L. decemlineata. Moreover, vATPase subunit E is a pesticide inducible gene and may play a role in pesticide toxicity.

The N termini of a-subunit isoforms are involved in signaling between vacuolar H+-ATPase (V-ATPase) and cytohesin-2

Previously, we reported an acidification-dependent interaction of the endosomal vacuolar H(+)-ATPase (V-ATPase) with cytohesin-2, a GDP/GTP exchange factor (GEF), suggesting that it functions as a pH-sensing receptor. Here, we have studied the molecular mechanism of signaling between the V-ATPase, cytohesin-2, and Arf GTP-binding proteins. We found that part of the N-terminal cytosolic tail of the V-ATPase a2-subunit (a2N), corresponding to its first 17 amino acids (a2N(1-17)), potently modulates the enzymatic GDP/GTP exchange activity of cytohesin-2. Moreover, this peptide strongly inhibits GEF activity via direct interaction with the Sec7 domain of cytohesin-2. The structure of a2N(1-17) and its amino acids Phe(5), Met(10), and Gln(14) involved in interaction with Sec7 domain were determined by NMR spectroscopy analysis. In silico docking experiments revealed that part of the V-ATPase formed by its a2N(1-17) epitope competes with the switch 2 region of Arf1 and Arf6 for binding to the Sec7 domain of cytohesin-2. The amino acid sequence alignment and GEF activity studies also uncovered the conserved character of signaling between all four (a1-a4) a-subunit isoforms of mammalian V-ATPase and cytohesin-2. Moreover, the conserved character of this phenomenon was also confirmed in experiments showing binding of mammalian cytohesin-2 to the intact yeast V-ATPase holo-complex. Thus, here we have uncovered an evolutionarily conserved function of the V-ATPase as a novel cytohesin-signaling receptor.

Structural divergence of the rotary ATPases

The rotary ATPase family of membrane protein complexes may have only three members, but each one plays a fundamental role in biological energy conversion. The F1Fo-ATPase (F-ATPase) couples ATP synthesis to the electrochemical membrane potential in bacteria, mitochondria and chloroplasts, while the vacuolar H+-ATPase (V-ATPase) operates as an ATP-driven proton pump in eukaryotic membranes. In different species of archaea and bacteria, the A1Ao-ATPase (A-ATPase) can function as either an ATP synthase or an ion pump. All three of these multi-subunit complexes are rotary molecular motors, sharing a fundamentally similar mechanism in which rotational movement drives the energy conversion process. By analogy to macroscopic systems, individual subunits can be assigned to rotor, axle or stator functions. Recently, three-dimensional reconstructions from electron microscopy and single particle image processing have led to a significant step forward in understanding of the overall architecture of all three forms of these complexes and have allowed the organisation of subunits within the rotor and stator parts of the motors to be more clearly mapped out. This review describes the emerging consensus regarding the organisation of the rotor and stator components of V-, A- and F-ATPases, examining core similarities that point to a common evolutionary origin, and highlighting key differences. In particular, it discusses how newly revealed variation in the complexity of the inter-domain connections may impact on the mechanics and regulation of these molecular machines.

The NMR solution structure of subunit G (G(61)(-)(101)) of the eukaryotic V1VO ATPase from Saccharomyces cerevisiae

Subunit G is an essential stalk subunit of the eukaryotic proton pump V(1)V(O) ATPase. Previously the structure of the N-terminal region, G(1)(-)(59), of the 13kDa subunit G was solved at higher resolution. Here solution NMR was performed to determine the structure of the recombinant C-terminal region (G(61)(-)(101)) of subunit G of the Saccharomyces cerevisiae V(1)V(O) ATPase. The protein forms an extended alpha-helix between residues 64 and 100, whereby the first five- and the last residues of G(61)(-)(101) are flexible. The surface charge distribution of G(61)(-)(101) reveals an amphiphilic character at the C-terminus due to positive and negative charge distribution at one side and a hydrophobic surface on the opposite side of the structure. The hydrophobic surface pattern is mainly formed by alanine residues. The alanine residues 72, 74 and 81 were exchanged by a single cysteine in the entire subunit G. Cysteines at positions 72 and 81 showed disulfide formation. In contrast, no crosslink could be formed for the mutant Ala74Cys. Together with the recently determined NMR solution structure of G(1)(-)(59), the presented solution structure of G(61)(-)(101) enabled us to present a first structural model of the entire subunit G of the S. cerevisiae V(1)V(O) ATPase.

Assembly of subunit d (Vma6p) and G (Vma10p) and the NMR solution structure of subunit G (G(1-59)) of the Saccharomyces cerevisiae V(1)V(O) ATPase

Understanding the structural traits of subunit G is essential, as it is needed for V(1)V(O) assembly and function. Here solution NMR of the recombinant N- (G(1-59)) and C-terminal segment (G(61-114)) of subunit G, has been performed in the absence and presence of subunit d of the yeast V-ATPase. The data show that G does bind to subunit d via its N-terminal part, G(1-59) only. The residues of G(1-59) involved in d binding are Gly7 to Lys34. The structure of G(1-59) has been solved, revealing an alpha-helix between residues 10 and 56, whereby the first nine- and the last three residues of G(1-59) are flexible. The surface charge distribution of G(1-59) reveals an amphiphilic character at the N-terminus due to positive and negative charge distribution at one side and a hydrophobic surface on the opposite side of the structure. The C-terminus exhibits a strip of negative residues. The data imply that G(1-59)-d assembly is accomplished by hydrophobic interactions and salt-bridges of the polar residues. Based on the recently determined NMR structure of segment E(18-38) of subunit E of yeast V-ATPase and the presently solved structure of G(1-59), both proteins have been docked and binding epitopes have been analyzed.