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

• Published in: BMC biology Vol. 21; no. 1; p. 47
• Main Authors: Kahle, Maximilian, Appelgren, Sofia, Elofsson, Arne, Carroni, Marta, Ädelroth, Pia
• Format: Journal Article
• Language: English
• Published: England BioMed Central Ltd 28-02-2023; BioMed Central; BMC
• Subjects: AAA Proteins; AAA+; Adenosine triphosphatase; AlphaFold; Analysis; ATPase; Binding; Binding sites; Carboxylates; cNOR; Cryo-EM; Cytochrome; Cytochrome c; Cytochromes; Drugs; E coli; FeB; Heme; Hydrolysis; Insertion; Iron; Metalloproteins; Methods; Molecular Chaperones; MoxR; Nitric oxide; Nitric oxide reductase; nor accessory genes; Norethindrone; Paracoccus denitrificans; Protein families; Protein remodeling; Proteins; Reductases; Structure-Activity Relationship; Structure-activity relationship (Pharmacology); Structure-activity relationships; Structure-function relationships; Von Willebrand factor; VWA; Sweden; cNOR; VWA; FeB; AAA+; Nitric oxide reductase; nor accessory genes; ATPase; AlphaFold; Cryo-EM; Protein remodeling; MoxR; Iron
• ISSN: 1741-7007; 1741-7007
• DOI: 10.1186/s12915-023-01546-w

NorQ, a member of the MoxR-class of AAA+ ATPases, and NorD, a protein containing a Von Willebrand Factor Type A (VWA) domain, are essential for non-heme iron (Fe
) cofactor insertion into cytochrome c-dependent nitric oxide reductase (cNOR). cNOR catalyzes NO reduction, a key step of bacterial denitrification. This work aimed at elucidating the specific mechanism of NorQD-catalyzed Fe
insertion, and the general mechanism of the MoxR/VWA interacting protein families.
We show that NorQ-catalyzed ATP hydrolysis, an intact VWA domain in NorD, and specific surface carboxylates on cNOR are all features required for cNOR activation. Supported by BN-PAGE, low-resolution cryo-EM structures of NorQ and the NorQD complex show that NorQ forms a circular hexamer with a monomer of NorD binding both to the side and to the central pore of the NorQ ring. Guided by AlphaFold predictions, we assign the density that "plugs" the NorQ ring pore to the VWA domain of NorD with a protruding "finger" inserting through the pore and suggest this binding mode to be general for MoxR/VWA couples.
Based on our results, we present a tentative model for the mechanism of NorQD-catalyzed cNOR remodeling and suggest many of its features to be applicable to the whole MoxR/VWA family.