ATPases conformational changes

A minimal mechanism for Na, K -ATPase postulates that the enzyme cycles between two principal conformations, denoted Ej and Eg (Figure 10.11). El has a high affinity for Na and ATP and is rapidly phosphorylated in the presence of Mg to form Ei-P, a state which contains three oeeluded Na ions (occluded in the sense that they are tightly bound and not easily dissociated from the enzyme in this conformation). A conformation change yields Eg-P, a form of the enzyme with relatively low affinity for Na, but a high affinity for K. This state presumably releases 3 Na ions and binds 2 ions on the outside of the cell. Dephosphorylation leaves EgKg, a form of the enzyme with two... 

Dynein, kinesin, and myosin are motor proteins with ATPase activity that convert the chemical bond energy released by ATP hydrolysis into mechanical work. Each motor molecule reacts cyclically with a polymerized cytoskeletal filament in this chemomechanical transduction process. The motor protein first binds to the filament and then undergoes a conformational change that produces an increment of movement, known as the power stroke. The motor protein then releases its hold on the filament before reattaching at a new site to begin another cycle. Events in the mechanical cycle are believed to depend on intermediate steps in the ATPase cycle. Cytoplasmic dynein and kinesin walk (albeit in opposite... 

Mutations in another region, the second cytoplasmic loop between M2 and M3 in Ca-ATPase of sarcoplasmic reticulum (Thr ->Ala, Gly -t Ala, and Glu Gln) also result in a complete loss of Ca-transport and Ca-ATPase activity associated with a dramatic reduction in the rate of phosphoenzyme turnover [96]. These mutations do not affect the affinity of the enzyme for Pj and therefore resemble the Pro mutants [123] in that they affect only the E1P-E2P conformational change and not the affinities for ATP, Ca or Pj. 

Conformational changes within or near the ATP-binding site of H,K-ATPase have also been demonstrated with the reversible fluorescent probes TNP-ATP [97,98] and... 

Recently Rabon et al. [100] reported on a new conformational probe of H,K-ATPase. This fluorescent quinoline derivative MDPQ was shown to be a reversible luminal K -site inhibitor of both K -ATPase and K -pNPPase activity. High-affinity MgATP binding induced a conformational change with fluorophore movement into a more hydrophobic environment. 

The conformational changes which have been described so far are probably all relatively small local changes in the structure of H,K-ATPase. This has been confirmed by Mitchell et al. [101] who demonstrated by Fourier transform infrared spectroscopy that a gross change in the protein secondary structure does not occur upon a conformational change from Ei to 3. Circular dichroism measurements, however [102,103], indicated an increase in a-helical structure upon addition of ATP to H,K-ATPase in the presence of Mg and... 

Kane DJ, Fendler K, Grell E et al (1997) Stopped-flow kinetic investigations of conformational changes of pig kidney Na+,K+-ATPase. Biochemistry 36 13406-13420... 

Wang, J., Song, J. J., Seong, I. S., Franklin, M. C., Kamtekar, S., Eom, S. H., and Chung, C. H. Nucleotide-dependent conformational changes in a protease-associated ATPase HslU. Structure fCambJ 2001b, 9, 1107-1116. 

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