Abstract
P-type ATPases are a large family of membrane transporters that are found in all forms of life. These enzymes couple ATP hydrolysis to the transport of various ions or phospholipids across cellular membranes, thereby generating and maintaining crucial electrochemical potential gradients. P-type ATPases have been studied by a variety of methods that have provided a wealth of information about the structure, function, and regulation of this class of enzymes. Among the many techniques used to investigate P-type ATPases, the electrical method based on solid supported membranes (SSM) was employed to investigate the transport mechanism of various ion pumps. In particular, the SSM method allows the direct measurement of charge movements generated by the ATPase following adsorption of the membrane-bound enzyme on the SSM surface and chemical activation by a substrate concentration jump. This kind of measurement was useful to identify electrogenic partial reactions and localize ion translocation in the reaction cycle of the membrane transporter. In the present review, we discuss how the SSM method has contributed to investigate some key features of the transport mechanism of P-type ATPases, with a special focus on sarcoplasmic reticulum Ca2+-ATPase, mammalian Cu+-ATPases (ATP7A and ATP7B), and phospholipid flippase ATP8A2.
Highlights
P-type ATPases constitute a superfamily of membrane transporters that are present in all forms of life and are located in various membrane types, such as the plasma or cellular organelle membranes.The superfamily of P-type ATPases is classified into five distinct subfamilies (P1–P5), which are specific to different substrates [1,2,3]
solid supported membranes (SSM) measurements on ATP7A and ATP7B revealed that ATP-induced charge movement in these enzymes is not changed by alkaline or acid pH [48], as shown by charge transfer measurements at different pH values (Figure 5B)
The results of this study demonstrated the absence of H+ countertransport in the Cu+ translocation cycle of EcCopA, qualifying EcCopA as an electrogenic uniporter
Summary
P-type ATPases constitute a superfamily of membrane transporters that are present in all forms of life and are located in various membrane types, such as the plasma or cellular organelle membranes. The superfamily of P-type ATPases is classified into five distinct subfamilies (P1–P5), which are specific to different substrates [1,2,3] These enzymes use the energy provided by ATP hydrolysis to transport various ions or phospholipids across cellular membranes, thereby generating and maintaining essential electrochemical potential gradients. Is the accepted of two the the catalytic cycle of P-type ATPases ATPase protein canmodel assume catalytic cycle of According to this model, the ATPase protein can assume two main main conformational states, denoted E1 and E2, with different affinity for the transported ions and conformational. E2Pand is followed byaccelerating proton translocation release to the transition, which completes the catalytic and transport cycle.
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