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Fig. 10 | BMC Biology

Fig. 10

From: Insights into the structure-function relationship of the NorQ/NorD chaperones from Paracoccus denitrificans reveal shared principles of interacting MoxR AAA+/VWA domain proteins

Fig. 10

Proposed mechanism of cNOR activation by NorQD based on the presented data. a Structure models for the P. denitrificans cNOR based on PDB ID: 3O0R [5], overall arrangement of the NorQD complex based on our cryo-EM data, detailed structures of NorD and NorQ protein based on 6L1Q (CbbQ for NorQ) and the predicted structure of NorD (Fig. 7a), respectively. b Step 1: Hexameric NorQ (pink/magenta) uses one NorD (blue) as an adaptor protein in order to bind the apo-form of cNOR (gray, the suggested “immature” nature of this form indicated by the larger accessibility of the acidic patch). Interaction of NorQD with cNOR occurs via the MIDAS site on the NorD VWA domain binding to D220/E222 on NorB (light gray). Step 2: NorQ induces ATP hydrolysis-powered conformational changes in cNOR via the “finger” from the NorD VWA domain inserted into the hexamer pore. These conformational changes would then propagate from the NorD VWA via the NorB surface further up the TM helix VII, modulating accessibility and/or affinity of the Fe binding site. The inset (*) shows how the “finger”/H2I region in our model is structurally indirectly connected to the FeB site in cNOR. Step 3: Once cNOR has acquired the FeB cofactor and gained/restored functionality, the NorQD complex unbinds cNOR

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