6uyk | pdb_00006uyk
Dark-operative protochlorophyllide oxidoreductase in the nucleotide-free form.
Structural highlights
Function[BCHL_RHOS4] Component of the dark-operative protochlorophyllide reductase (DPOR) that uses Mg-ATP and reduced ferredoxin to reduce ring D of protochlorophyllide (Pchlide) to form chlorophyllide a (Chlide). This reaction is light-independent. The L component serves as a unique electron donor to the NB-component of the complex, and binds Mg-ATP.[HAMAP-Rule:MF_00355][1] Publication Abstract from PubMedA key step in bacteriochlorophyll biosynthesis is the reduction of protochlorophyllide to chlorophyllide, catalyzed by dark-operative protochlorophyllide oxidoreductase (DPOR). DPOR contains two [4Fe-4S]-containing component proteins (BchL and BchNB) that assemble upon ATP binding to BchL to coordinate electron transfer and protochlorophyllide reduction. But the precise nature of the ATP-induced conformational changes are poorly understood. We present a crystal structure of BchL in the nucleotide-free form where a conserved, flexible region in the N-terminus masks the [4Fe-4S] cluster at the docking interface between BchL and BchNB. Amino acid substitutions in this region produce a hyper-active enzyme complex, suggesting a role for the N-terminus in auto-inhibition. Hydrogen deuterium exchange mass spectrometry shows that ATP-binding to BchL produces specific conformational changes leading to release of the flexible N-terminus from the docking interface. The release also promotes changes within the local environment surrounding the [4Fe-4S] cluster and promotes BchL complex formation with BchNB. A key patch of amino acids, Asp-Phe-Asp (the 'DFD patch'), situated at the mouth of the BchL ATP-binding pocket promotes inter-subunit cross stabilization of the two subunits. A linked BchL dimer with one defective ATP-binding site does not support protochlorophyllide reduction, illustrating nucleotide binding to both subunits as a prerequisite for the inter-subunit cross stabilization. The masking of the [4Fe-4S] cluster by the flexible N-terminal region and the associated inhibition of activity is a novel mechanism of regulation in metalloproteins. Such mechanisms are possibly an adaptation to the anaerobic nature of eubacterial cells with poor tolerance for oxygen. The flexible N-terminus of BchL autoinhibits activity through interaction with its [4Fe-4S] cluster and relieved upon ATP binding.,Corless EI, Saad Imran SM, Watkins MB, Bacik JP, Mattice J, Patterson A, Danyal K, Soffe M, Kitelinger R, Seefeldt LC, Origanti SS, Bennett B, Bothner B, Ando N, Antony E J Biol Chem. 2020 Nov 20:100107. doi: 10.1074/jbc.RA120.016278. PMID:33219127[2] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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