ATPase

ATPase is an enzyme which catalyzes the breakdown of ATP into ADP and a phosphate ion. This dephosphorylation releases energy which the enzyme uses to drive other reactions. ATPAse types include:

• F-ATPase - the prime producers of ATP;
  
• V-ATPase or Vacuolar-type H+ ATPase couples the energy to proton transport across membranes;
  
• A-ATPase are found in archaea. For details see A-ATP Synthase;
  
• P-ATPase transport ions;
  
• E-ATPase hydrolyze extracellular ATP.
  
• MipZ is an ATPase which forms a complex with the chromosome partitioning protein ParB and is responsible for the regulation of FtsZ ring formation.
  

ATPase domains include metal-binding domain (MBD) and nucleotide-binding domain (NBD). For more details see:

• Cu transporting ATPase are in P(1B)-Type Cu(I) Transporting ATPases ATP7A and ATP7B.
  
• Na/K transporting ATPase are in Sodium-Potassium ATPase.
  
• H/K transporting ATPase are in Esomeprazole and H+/K+ - ATPase Interaction.
  
• Transitional endoplasmic reticulum ATPase are in Valosin Containing Protein D120.
  
• Central stalk in F(1)-ATPase is described in A-ATP Synthase.

Structural and functional insights into a dodecameric molecular machine – The RuvBL1/RuvBL2 complex (ATPase)^[1]
(RuvB-like 1; 2c9o ^[2]; colored magenta) and its homolog RuvBL2 are evolutionarily highly conserved AAA+ ATPases essential for many cellular activities. They play an important role in chromatin remodeling, transcriptional regulation and DNA damage repair. RuvBL1 and RuvBL2 are overexpressed in different types of cancer and interact with major oncogenic factors, such as β-catenin and c-myc regulating their function. Since the full-length complex did not crystallize, were generated: (R1∆DII) and (R2∆DII). Crystals of the selenomethionine derivative of the R1∆DII/R2∆DII complex diffracted to 3 Å resolution and led to the determination of the three-dimensional structure of the complex. The structure reveals a (the RuvBL1 and the RuvBL2 are colored darkmagenta and cyan, respectively) bound to ADP/ATP (click on or, alternatively on to see protein/nucleotide interactions). The two heterohexamers interact with each other via the retained part of domain II, which is however poorly visible in the electron density maps, probably because the complex was not crystallized in a single conformational state. This is also hinted by evidence that in the RuvBL1 monomers, ATP was partly hydrolyzed to ADP. The dodecameric quaternary structure of the R1ΔDII/R2ΔDII complex observed in the crystal structure was confirmed by small-angle X-ray scattering analysis. RuvBL1 and RuvBL2 share . Due to the low data resolution, and even though the crystal structure could be solved by molecular replacement using a truncated RuvBL1 model, the use of a selenomethionine derivative was essential to elucidate the complex composition, since only one methionine residue is conserved out of 11 in R1ΔDII and 12 in R2ΔDII. Interestingly, truncation of domain II led to a substantial increase in ATP consumption of RuvBL1, RuvBL2 and their complex. In addition, we present evidence that DNA unwinding of the human RuvBL proteins can be auto-inhibited by domain II, which is not present in the homologous bacterial helicase RuvB. The alternation of charges in the central channel of the dodecamer shown below, combined with the diameter of the channel (ranging between 17 and 21 Å) suggests interactions with single-stranded nucleic acids.

Electrostatic potential mapped at the molecular surface for the R1deltaDII/R2deltaDII dodecamer. (a) top view and (b) cross-section view showing the central channel. (c) cross-section view of the SV40 Ltag hexamer complexed with ATP (PDB 1svm), included for comparison. In (a) and (b) the R1deltaDII and R2deltaDII monomers are colored gold and cyan, respectively. In (c) the SV40 monomers are alternately colored gold and cyan.

Our data give new insights into the molecular arrangement of RuvBL1 and RuvBL2 and strongly suggest that in vivo activities of these highly interesting therapeutic drug targets are regulated by cofactors inducing conformational changes via domain II in order to modulate the enzyme complex into its active state.