Vacuolar ATPases

Struve, I., Weber, A., Liittge, U., Ball, E. Smith, J.A.C. (1985). Increased vacuolar ATPase activity correlated with CAM induction in Mesembryanthemum crystallinum and Kalanchoe blossfeldiana cv. Tom Thumb. Journal of Plant Physiology, 117, 451-68. 

Clague Ml, Urbe S, Aniento F, Gruenberg J. Vacuolar ATPase activity is required for endosomal carrier vesicle formation. J Biol Chem 1994 269(1) 21-24. 

Two other types of proton-pumping ATPases are considered in Chapter 18. One is the mitochondrial F,F0 ATPase, which ordinarily operates in the reverse direction as the body s principal ATP synthase. The other type, which in some ways resembles the mitochondrial FjFq ATPase, is the vacuolar ATPase (V-ATPase). These are true proton pumps which acidify vacuoles of plants and also lysosomes and phagocytic vacuoles.554 555 They are also considered in Chapter 18. 

One of the first inteins discovered was found in the 119-kDa precursor to a subunit of a vacuolar ATPase of yeast.a,c In this 50-kDa intein Thr 72, His 75, and His 197 may have catalytic functions.d The intein is spliced out to form the 69-kDa subunit. 

The F-, V-, and A-ATPases constitute a family of ATP hydrolysis-driven ion pumps which are found in Archaea, eubacteria, simple eukaryotes such as yeast, and higher eukaryotes including plants and mammals. The family of ion pumps is divided into three subfamilies the F-ATPases (which function mainly as ATP synthases), the vacuolar ATPases (which function solely as ATP hydrolysis-driven ion pumps) and the Archaeal A-type ATPases (whose function can be either in the direction of ATP synthesis or hydrolysis). All three members of the family are evolutionarily related, and it is believed that the three subfamilies have arisen from a common ancestor. 

Subunit Composition of the FiF0-ATP Synthase, the Eukaryotic Vacuolar ATPase and the Archaeal A-ATPase... 

AThe subunit has been confirmed for the insect (Merzendorfer et al, 1999) and chromaffin granule enzyme (Ludwig et al, 1998) and has recently been found in the yeast enzyme (Sambade and Kane, 2004). The subunit compositions of the F-ATPase from the bacterium Escherichia coli, the vacuolar ATPase from yeast and bovine brain clathrin-coated vesicles, and the A-ATPase from the Archaeon Thermoplasma acidophilum are listed. Molecular masses are calculated from the amino acid sequence where available. 

Fig. 1. Working models of the F-, V-, and A-ATPases. Model of the subunit arrange-mentin the (A) FjFo-ATP synthase from Escherichia colt, (B) vacuolar ATPase from bovine brain clathrin- coated vesicles, and (C) A A0-ATPase from Thermoplasma acidophilum. The catalytic domain is in blue, the rotor domain is in green, and the stator domain is in orange.

In the cell, the vacuolar ATPase functions exclusively as an ATP hydrolysis-driven proton pump. This functional preference of the vacuolar ATPase seems not to be due to a fundamental structural difference compared with the ATP synthase because it has been shown that the V-ATPase can be reversed to synthesize ATP in vitro, albeit with very low efficiency (Hirata et al., 2000). 

Fig. 3. Electron microscopy of the Escherichia coli FjFo-ATP synthase and the bovine brain vacuolar ATPase (A) Projection image of the E. coli F-ATPase (Wilkens, 2000). The positions of subunit a (large black arrowhead), the peripheral stalk (white arrow), the C-terminal domain of the 6-subunits (white arrowhead), and the 5-subunit (small black...

Dschida, W. J., and Bowman, B. J. (1992). Structure of the vacuolar ATPase from Neurospora crassa as determined by electron microscopy. J. Biol Chem. 267, 18783-18789. 

Wilkens, S., and Forgac, M. (2001). Three-dimensional structure of the vacuolar ATPase proton channel by electron microscopy. / Biol. Chem. 276, 44064-44068. 

Wilkens, S., Zhang, Z., and Zheng, Y. (2005). A structural model of the vacuolar ATPase from transmission electron microscopy. Micron 36, 109-126. 

Roush et al. applied the diastereoselective crotylboration methodology in the total synthesis of bafilomycin Ai (66), a potent vacuolar ATPase inhibitor that displays broad antibiotic activity27 (Scheme 3.lx). In the synthesis, the known aldehyde (R)-67 was treated with ( )-crotylboronate (R,R)-43E to provide an 85 15 mixture of the homoallylic alcohol 68 and the undesired 3,4-anti-4,5-syn diastereomer with an isolated 78% yield of 68. Alcohol protection as a TBS ether followed by hydroboration mediated by Wilkinson s catalyst efficiently provided the primary alcohol 69. 

Vacuolar ATPase subunit H Enriched in amyloid plaques Liao et al. 2004... 

Figure 5. Components and processes of a membrane-bound organelle, representing either a Protein Storage Vacuole (PSV) or a membrane-bound globoid found within a compound PSV V-PPase = vacuolar inorganic pyrophosphatase. V-ATPase = vacuolar ATPase. TIP = Tonoplast Intrinsic Protein. Ptdlns = phosphatidylinositol. DAG = diacylglycerol. Questionmarks indicate purely speculative aspects of the diagram.

The enzyme proved to be composed of four types of subunits (87, 60, 29 and 20 kDa). The subunit ratio was assumed to be equal to 3 3 1 1 [66]. The sequences of major subunits showed significant (more than 50%) homology with the detachable sector of eukaryotic vacuolar (V-type) H -ATPase. On the other hand, homology with bacterial Fi ATPase proved to be less than 30%. Since the above-mentioned inhibitor pattern is, in fact, identical with those of the vacuolar ATPase, one might assume that halobacterial ATPase corresponds to the V-type. However, the sequence of proteolipid (c subunit) of... 

Three types of ATP-driven cation pumps can be distinguished on the basis of their structure and their sensitivity to inhibitors. They are the E E2-ATPases, the FiFo-proton-translocating ATP synthase, and the vacuolar ATPases which are designated as P-, F-, and V-type ATPases, respectively [37]. Several of the distinguishing characteristics of these enzymes are summarized in Table 1. The F- and V-ATPases can be differentiated by the sensitivity of the former to azide and the latter to nitrate and A-ethylmaleimide (NEM)[38]. In addition, the V-ATPases are exquisitely sensitive to the antibiotic bafilomycin A [39,40]. 

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