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  • Title: Cryo-EM structures of KdpFABC suggest a K+ transport mechanism via two inter-subunit half-channels.
    Author: Stock C, Hielkema L, Tascón I, Wunnicke D, Oostergetel GT, Azkargorta M, Paulino C, Hänelt I.
    Journal: Nat Commun; 2018 Nov 26; 9(1):4971. PubMed ID: 30478378.
    Abstract:
    P-type ATPases ubiquitously pump cations across biological membranes to maintain vital ion gradients. Among those, the chimeric K+ uptake system KdpFABC is unique. While ATP hydrolysis is accomplished by the P-type ATPase subunit KdpB, K+ has been assumed to be transported by the channel-like subunit KdpA. A first crystal structure uncovered its overall topology, suggesting such a spatial separation of energizing and transporting units. Here, we report two cryo-EM structures of the 157 kDa, asymmetric KdpFABC complex at 3.7 Å and 4.0 Å resolution in an E1 and an E2 state, respectively. Unexpectedly, the structures suggest a translocation pathway through two half-channels along KdpA and KdpB, uniting the alternating-access mechanism of actively pumping P-type ATPases with the high affinity and selectivity of K+ channels. This way, KdpFABC would function as a true chimeric complex, synergizing the best features of otherwise separately evolved transport mechanisms.
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