Cryo-EM structures of KdpFABC suggest a K+ transport mechanism via two inter-subunit half-channels.

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.

SUBMITTER: Stock C 

PROVIDER: S-EPMC6255902 | biostudies-literature | 2018 Nov

REPOSITORIES: biostudies-literature