ATPase proteolipid

The Vo is made of subunits acc c"de. Subunits c, c, and c" are proteolipid isoforms each containing one essential lipid-exposed glutamate residue. The proteolipids in the V-ATPase are twice the size compared with the F-ATPase proteolipids, and it is assumed that the four transmembrane a helix c- and c -subunits are a result of an early gene fusion event. Subunit c" has two lipid-exposed glutamates, but only one of them is essential for proton pumping. The 100-kDa subunit a is a two-domain protein with a... 

Muller V, Aufurth S, Rahlfs S. 2001. The Na -cycle in Acetobacterium woodii identification and characterization of a Na -translocating FiFo-ATPase with a mixed oligomer of 8 and 16-kDa proteolipids. Biochim Biophys Acta 1505 108-20. 

Rahlfs S, Aufurth S, Muller V. 1999. The Na -FiFo-ATPase operon from Acetobac-terium woodiv. operon structure and presence of multiple copies of atpE, which encode proteolipids of 8- and 18-kDa. J Biol Chem 274 33999 004. 

Activity is modulated by other proteins present in the membrane. These include a glycoprotein (MW 53 000) which stimulates ATPase activity 138 a 60 000 molecular weight protein, which is phosphorylated in a calmodulin-dependent fashion, affects accumulation of calcium 139 while the activity of the enzyme is affected by an endogenous kinase and phosphatase which phosphorylates and dephosphorylates the protein.140 Phospholamban is a proteolipid (MW 22 000) in cardiac SR which undergoes both cyclic AMP-dependent and calcium-calmodulin-dependent phosphorylation,141 but at different sites. All these proteins are probably involved in regulating the activity of the calcium pump. 

The subunit nomenclature for the A-ATPase is Kfor the proteolipid, I for the V- and F-ATPase a-subunit, and C for the V-ATPase subunit d. The small polypeptide called H in the A-ATPase is probably the homologue of the V-ATPase G-subunit. 

What is known is that the ( -subunits from different species are able to form rings of between 10 and 14 proteolipids. For example, the x-ray crystal structure of the yeast F-ATPase (Stock et at, 1999) shows that there are 10 e-subunits, whereas the chloroplast enzyme has 14 (Seelert et at,... 

Hilario, E., and Gogarten, J. P. (1998). The prokaryote-to-eukaryote transition reflected in the evolution of the V/F/A-ATPase catalytic and proteolipid subunits./ Mol. Evol. 46, 703-715. 

Mandel, M., Moriyama, Y., Hulmes.J. D., Pan, Y. C., Nelson, H., and Nelson, N. (1988). cDNA sequence encoding the 16-kDa proteolipid of chromaffin granules implies gene duplication in the evolution of H+-ATPases. Proc. Natl. Acad. Sci. USA 85, 5521-5524. 

A membrane-embedded hairpin structure for the c subunit was established from genetic studies.31 The role of cAsp-61 in the second membrane helix of the c subunit has been studied in detail the cAsp-61— Asn or Gly mutants showed no proton conduction or ATP synthesis.99 Binding of DCCD to this residue blocked proton conduction. These results are consistent with the notion that cAsp-61 is part of the proton pathway. The carboxyl residue at position 61 was able to be transferred to the corresponding position of the first helix.100 Vacuolar-type ATPase has a similar proteolipid subunit possibly evolved from the same ancestral protein as the c subunit.25 The vacuolar proteolipid has glutamate in the middle of the fourth membrane-spanning helix, corresponding to the position of c Asp-61 of the c subunit. The glutamate may play an important role in proton conduction similar to the c subunit.101 ... 

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... 

The nucleotide sequence derived from the gene for the DCCD-reactive proteolipid from S. acidocaldarius (strain 7) indicates that the peptide has an Mr of about 10 000 [67], A partial amino-acid sequence derived from the nucleotide sequence shows considerable homology with subunit c of F-ATPases but not the Mr 16000 proteolipid of V-type ATPases. It is proposed that the proteolipid associated with V-ATPases is a product of a gene that duplicated after the V- and archaeal ATPases had differentiated [67],... 

The sarcoplasmic reticulum (SR) calcium pump together with phosphorylation of specific proteins, has an important role in myocardial contraction and relaxation. Phospholamban, a 20-24 kDa proteolipid, is phosphorylated by cAMP-dependent protein kinase as well as calmodulin-dependent protein kinase. Phosphorylation of this protein results in stimulation of Ca +-ATPase and Ca + transport by the SR (Scheme 4.1.1). ... 

J Hermolin and RH Fillingame (1989) hT-ATPase activity of Escherichia coli F Fq is blocked after reaction of dicyclohexylcarbodllmide with a single proteolipid subunit c) of the Fq complex. J Biol Chem 264 3896-3903... 

Both cAMP-dependent and calmodulin-Ca2+ dependent phosphorylation of a proteolipid (phospholamban) of the protein kinases, result in stimulation of Ca2+ transport and Ca2+ dependent ATPase activities of sarcoplasmic reticulum (50, 31,... 

The main constituent of the membrane sector of F and V-ATPases is a highly hydrophobic polypeptide that binds DCCD, and on account of its solubility in chloroform/methanol was called proteolipid (20-23). In the F-ATPases and V-ATPases of archaebacteria the proteolipid is about 8 kDa and spans the membrane two times. 

FIGURE 2. A proposal for the initial steps in the evolution of F-ATPases. A symmetric hexameric structure is proposed. The catalytic sector was comprised of six identical subunits which evolved to the current 3 a and 3 P structure following the gene duplication. The hexameric form of the proteolipid is based on the identification of a functional hexamer in F-ATPases (26-30). However, ten to twelve copies were reported in other studies (31,32). 

Sato, N. Suzuki, N. Yamaguchi, M. Yamaguchi, N. Okuma, K. Proteolipid subunits of vacuolar H" -ATPase (ATP6F) as tumor antigens, application to cancer therapy, and use of proton pump inhibitor as anticancer agent. Jpn. Kokai Tokkyo Koho JP 2001286284,2001 Chem. Abstr. 2001,135, 314438. 

Similar results were obtained in reconstitution experiments with Upophilin and proteolipid apoprotein-lecithin systems, sarcoplasmic reticulum Ca +, Mg +-ATPase, rhodopsin, and glycophorin. In all these cases deuterium NMR revealed only one lipid population while the epr spectra (as far as available) showed two components. The results further show that proteins either disorder orhave little effect on hydrocarbon chain order in membranes above the gel-to-liquid crystal phase transition temperature, Tc, of the pure lipids. 

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