The Flexible N-Terminus of BchL Autoinhibits Activity Through Interaction With Its [4Fe-4S] Cluster and Released Upon ATP Binding
Document Type
Article
Journal/Book Title
Journal of Biological Chemistry
Publication Date
1-4-2020
Publisher
Elsevier Inc.
Volume
296
First Page
1
Last Page
15
Abstract
A key step in bacteriochlorophyll biosynthesis is the reduction of protochlorophyllide to chlorophyllide, catalyzed by dark-operative protochlorophyllide oxidoreductase. Darkoperative protochlorophyllide oxidoreductase 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 is 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 hyperactive enzyme complex, suggesting a role for the N-terminus in autoinhibition. 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 intersubunit cross stabilization of the two subunits. A linked BchL dimer with one defective ATPbinding site does not support protochlorophyllide reduction, illustrating nucleotide binding to both subunits as a prerequisite for the intersubunit cross stabilization. The masking of the [4Fe-4S] cluster by the flexible N-terminal region and the associated inhibition of the 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.
Recommended Citation
Corless, E. I., Imran, S. M. S., Watkins, M. B., Bacik, J.-P., Mattice, J., Patterson, A., Danyal, K., Soffe, M., Kitelinger, R., Seefeldt, L. C., Origanti, S. S., Bennett, B., Bothner, B., Ando, N., and Antony, E. (2020) The flexible N-terminus of BchL autoinhibits activity through interaction with its [4Fe-4S] cluster and relieved upon ATP binding. J. Biol. Chem. 296, 100107.
