ATPase complex bacterial

Aspects of four energy-transducing systems which can play an important role in bacterial energy metabolism will be discussed electron-transfer systems, the, Mg -activated ATPase complex, bacteriorhodopsin and secondary solute transport... 

Strongly curved membranes. For instance, in the study of bacterial photosynthetic membranes, a number of questions have not been addressed by AFM, like the location of the c d bc and ATPase complexes. The development of recognition imaging techniques, such as immuno-AFM, and the combination of AFM and confocal microscope are anticipated to overcome the difficulties. 

The transport of EDTA into a bacterial strain capable of its degradation has been examined (Witschel et al. 1997). Inhibition was observed with DCCD (ATPase inhibitor), nigericin (dissipates ApH), but not valinomycin (dissipates Av /), and was dependent on the stability constant of metal-EDTA complexes. 

F-ATPases (including the H+- or Na+-translocating subfamilies F-type, V-type and A-type ATPase) are found in eukaryotic mitochondria and chloroplasts, in bacteria and in Archaea. As multi-subunit complexes with three to 13 dissimilar subunits, they are embedded in the membrane and involved in primary energy conversion. Although extensively studied at the molecular level, the F-ATPases will not be discussed here in detail, since their main function is not the uptake of nutrients but the synthesis of ATP ( ATP synthase ) [127-130]. For example, synthesis of ATP is mediated by bacterial F-type ATPases when protons flow through the complex down the proton electrochemical gradient. Operating in the opposite direction, the ATPases pump 3 4 H+ and/or 3Na+ out of the cell per ATP hydrolysed. 

Although extensive biochemical data on both the bacterial and eukaryotic ATP-dependent proteases are available, the characterization of these proteolytic machines at atomic resolution has proven difficult, because of both the large size of these complexes and their lability to proteolysis and dissociation. No structural data at all are currently available for Lon and the mitochondrial ATP-dependent proteases. In the case of the cytosolic, membrane-integrated bacterial protease FtsH, atomic resolution data are available only for the ATPase domain (Krzywda et al. 2002 Niwa et al. 2002). In contrast, the ATP-dependent activators of the ClpAP and ClpXP proteolytic machines have so far resisted crystallization. Atomic resolution data are available only for the proteolytic component ClpP (Wang et al. 1997), and separately for a ClpX monomer (Kim and Kim 2003) and a ClpA monomer (Guo et al. 2002b). 

The Mg2+-activated ATPase (or ATP synthase) is made up of two parts. The Fj component is the catalytic, Mg2+-binding, extrinsic membrane protein composed of five different subunits, a, (3, y, S and e. The F0 component is an intrinsic membrane complex that contains three subunits, a, b and c, and mediates proton translocation. The F, protein is bound to the membrane through interaction with F0. The complexity of the F,F0 enzyme has presented many difficulties. Hie greatest advances have been made for the bacterial enzymes, notably for thermophiles, Escherichia coli and Rhodospirillum rubrum, where progress has been made in the purification of subunits and their reconstitution into membranes, and the identification of binding sites for Mg2+ and nucleotides on the Fi subunits.300 FiF0 preparations can be incorporated into liposomes and display H+ translocation, ATP-P, exchange and ATP synthesis.301... 

Copper ion homeostasis in prokaryotes involves Cu ion efflux and sequestration. The proteins involved in these processes are regulated in their biosynthesis by the cellular Cu ion status. The best studied bacterial Cu metalloregulation system is found in the gram-positive bacterium Enterococcus hirae. Cellular Cu levels in this bacterium control the expression of two P-type ATPases critical for Cu homeostasis (Odermatt and Solioz, 1995). The CopA ATPase functions in Cu ion uptake, whereas the CopB ATPase is a Cu(I) efflux pump (Solioz and Odermatt, 1995). The biosynthesis of both ATPases is regulated by a Cu-responsive transcription factor, CopY (Harrison et al., 2000). In low ambient Cu levels Cop Y represses transcription of the two ATPase genes. On exposure to Cu(I), CopY dissociates from promoter/operator sites on DNA with a for Cu of 20 jlM (Strausak and Solioz, 1997). Transcription of copA and copB proceeds after dissociation of CuCopY. The only other metal ions that induce CopY dissociation from DNA in vitro are Ag(I) and Cd(II), although the in vivo activation of copA and copB is specihc to Cu salts. The CuCopY complex is dimeric with two Cu(I) ions binding per monomer (C. T. Dameron, personal communication). The structural basis for the Cu-induced dissociation of CopY is unknown. Curiously, CopY is also activated in Cu-dehcient cells, but the mechanism is distinct from the described Cu-induced dissociation from DNA (Wunderh-Ye and Solioz, 1999). 

Figure 9 Yeast5. cerevisiae cell with small daughter cell bud and proteins of arsenate reduction and transport. Acr2p the yeast cytoplasmic arsenate reductase. Acr3p the potential-driven membrane arsenite efflux protein, equivalent to bacterial ArsB. Ycflp the novel As(III)-3 GSH adduct carrier than transports the adduct complex into the cell vacuole compartment, functioning as an ATPase.

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