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Kapetanaki SM, Fekete Z, Dorlet P, Vos MH, Liebl U, Lukacs A. Molecular insights into the role of heme in the transcriptional regulatory system AppA/PpsR. Biophys J 2022; 121:2135-2151. [PMID: 35488435 DOI: 10.1016/j.bpj.2022.04.031] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2021] [Revised: 03/07/2022] [Accepted: 04/26/2022] [Indexed: 11/30/2022] Open
Abstract
Heme has been shown to have a crucial role in the signal transduction mechanism of the facultative photoheterotrophic bacterium Rhodobacter sphaeroides. It interacts with the transcriptional regulatory complex AppA/PpsR in which AppA and PpsR function as the antirepressor and repressor, respectively of photosynthesis gene expression. The mechanism, however of this interaction remains incompletely understood. In this study, we combined EPR spectroscopy and FRET to demonstrate the ligation of heme in PpsR with a proposed cysteine residue. We show that heme binding in AppA affects the fluorescent properties of the dark-adapted state of the protein, suggesting a less constrained flavin environment compared to the absence of heme and the light-adapted state. We performed ultrafast transient absorption measurements in order to reveal potential differences in the dynamic processes in the full-length AppA and its heme-binding domain alone. Comparison of the CO-binding dynamics demonstrates a more open heme pocket in the holo-protein, qualitatively similar to what has been observed in the CO sensor RcoM-2, and suggests a communication path between the BLUF and SCHIC domains of AppA. We have also examined quantitatively, the affinity of PpsR to bind to individual DNA fragments of the puc promoter using fluorescence anisotropy assays. We conclude that oligomerization of PpsR is initially triggered by binding of one of the two DNA fragments and observe a ∼10-fold increase in the dissociation constant Kd for DNA binding upon heme binding to PpsR. Our study provides significant new insight at the molecular level on the regulatory role of heme that modulates the complex transcriptional regulation in R. sphaeroides and supports the two levels of heme signaling, via its binding to AppA and PpsR and via the sensing of gases like oxygen.
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Affiliation(s)
- Sofia M Kapetanaki
- Department of Biophysics, Medical School, University of Pécs, 7624 Pécs, Hungary; Szentagothai Research Center, University of Pecs, 7624 Pécs, Hungary.
| | - Zsuzsanna Fekete
- Department of Biophysics, Medical School, University of Pécs, 7624 Pécs, Hungary
| | - Pierre Dorlet
- Aix Marseille Univ, CNRS, BIP, IMM, Marseille, France
| | - Marten H Vos
- LOB, CNRS, INSERM, Ecole Polytechnique, Institut Polytechnique de Paris, 91128 Palaiseau Cedex, France
| | - Ursula Liebl
- LOB, CNRS, INSERM, Ecole Polytechnique, Institut Polytechnique de Paris, 91128 Palaiseau Cedex, France
| | - Andras Lukacs
- Department of Biophysics, Medical School, University of Pécs, 7624 Pécs, Hungary; Szentagothai Research Center, University of Pecs, 7624 Pécs, Hungary.
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Heintz U, Meinhart A, Winkler A. Multi-PAS domain-mediated protein oligomerization of PpsR from Rhodobacter sphaeroides. ACTA CRYSTALLOGRAPHICA. SECTION D, BIOLOGICAL CRYSTALLOGRAPHY 2014; 70:863-76. [PMID: 24598755 PMCID: PMC3949515 DOI: 10.1107/s1399004713033634] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 09/27/2013] [Accepted: 12/12/2013] [Indexed: 01/04/2023]
Abstract
Per-ARNT-Sim (PAS) domains are essential modules of many multi-domain signalling proteins that mediate protein interaction and/or sense environmental stimuli. Frequently, multiple PAS domains are present within single polypeptide chains, where their interplay is required for protein function. Although many isolated PAS domain structures have been reported over the last decades, only a few structures of multi-PAS proteins are known. Therefore, the molecular mechanism of multi-PAS domain-mediated protein oligomerization and function is poorly understood. The transcription factor PpsR from Rhodobacter sphaeroides is such a multi-PAS domain protein that, in addition to its three PAS domains, contains a glutamine-rich linker and a C-terminal helix-turn-helix DNA-binding motif. Here, crystal structures of two N-terminally and C-terminally truncated PpsR variants that comprise a single (PpsRQ-PAS1) and two (PpsRN-Q-PAS1) PAS domains, respectively, are presented and the multi-step strategy required for the phasing of a triple PAS domain construct (PpsRΔHTH) is illustrated. While parts of the biologically relevant dimerization interface can already be observed in the two shorter constructs, the PpsRΔHTH structure reveals how three PAS domains enable the formation of multiple oligomeric states (dimer, tetramer and octamer), highlighting that not only the PAS cores but also their α-helical extensions are essential for protein oligomerization. The results demonstrate that the long helical glutamine-rich linker of PpsR results from a direct fusion of the N-cap of the PAS1 domain with the C-terminal extension of the N-domain that plays an important role in signal transduction.
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Affiliation(s)
- Udo Heintz
- Department of Biomolecular Mechanisms, Max Planck Institute for Medical Research, Heidelberg, Germany
| | - Anton Meinhart
- Department of Biomolecular Mechanisms, Max Planck Institute for Medical Research, Heidelberg, Germany
| | - Andreas Winkler
- Department of Biomolecular Mechanisms, Max Planck Institute for Medical Research, Heidelberg, Germany
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Winkler A, Heintz U, Lindner R, Reinstein J, Shoeman RL, Schlichting I. A ternary AppA-PpsR-DNA complex mediates light regulation of photosynthesis-related gene expression. Nat Struct Mol Biol 2013; 20:859-67. [PMID: 23728293 PMCID: PMC3702404 DOI: 10.1038/nsmb.2597] [Citation(s) in RCA: 60] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2012] [Accepted: 04/10/2013] [Indexed: 11/09/2022]
Abstract
The anoxygenic phototrophic bacterium Rhodobacter sphaeroides uses different energy sources, depending on environmental conditions including aerobic respiration or, in the absence of oxygen, photosynthesis. Photosynthetic genes are repressed at high oxygen tension, but at intermediate levels their partial expression prepares the bacterium for using light energy. Illumination, however, enhances repression under semiaerobic conditions. Here, we describe molecular details of two proteins mediating oxygen and light control of photosynthesis-gene expression: the light-sensing antirepressor AppA and the transcriptional repressor PpsR. Our crystal structures of both proteins and their complex and hydrogen/deuterium-exchange data show that light activation of AppA-PpsR2 affects the PpsR effector region within the complex. DNA binding studies demonstrate the formation of a light-sensitive ternary AppA-PpsR-DNA complex. We discuss implications of these results for regulation by light and oxygen, highlighting new insights into blue light-mediated signal transduction.
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Affiliation(s)
- Andreas Winkler
- Department of Biomolecular Mechanisms, Max Planck Institute for Medical Research, Heidelberg, Germany.
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Hisatomi O, Iwasa T, Kataoka M, Ebrey T. Introduction to the Symposium-in-Print on Photoreceptors and Signal Transduction in Honor of Professor Fumio Tokunaga. Photochem Photobiol 2008. [DOI: 10.1111/j.1751-1097.2008.00391.x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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