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

• Published in: Nature communications 2018-11, Vol.9 (1), p.4971-10, Article 4971
• Main Authors: Stock, C., Hielkema, L., Tascón, I., Wunnicke, D., Oostergetel, G. T., Azkargorta, M., Paulino, C., Hänelt, I.
• Format: Article
• Language: English
• Subjects: 101/28; 631/45/269/1151; 631/535/1258/1259; 631/57/2270/1140; 631/57/2283; 82/58; Activation; Binding sites; Biological membranes; Cations; Channels; Cryoelectron Microscopy; Crystal structure; Cytoplasm; Electron Spin Resonance Spectroscopy; Escherichia coli Proteins - chemistry; Escherichia coli Proteins - metabolism; Escherichia coli Proteins - ultrastructure; Humanities and Social Sciences; Ion Transport; Membranes; multidisciplinary; Phosphorylation; Potassium; Potassium - metabolism; Protein Conformation; Protein Subunits - chemistry; Protein Subunits - metabolism; Science; Science (multidisciplinary); Selectivity; Topology; Translocation; Transport
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/s41467-018-07319-2

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. The P-type ATPase subunit KdpB of KdpFABC hydrolyzes ATP while K + transport was assumed to occur through channel-like subunit KdpA. Here, the authors show two cryo-EM structures of KdpFABC which suggest a translocation pathway through two inter-subunit half-channels formed by KdpA and KdpB.