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PufQ regulates porphyrin flux at the haem/bacteriochlorophyll branchpoint of tetrapyrrole biosynthesis via interactions with ferrochelatase.

Authors
  • Chidgey, Jack W1
  • Jackson, Philip J1, 2
  • Dickman, Mark J2
  • Hunter, C Neil1
  • 1 Department of Molecular Biology and Biotechnology, University of Sheffield, Sheffield S10 2TN, UK.
  • 2 ChELSI Institute, Department of Chemical and Biological Engineering, University of Sheffield, Sheffield S1 3JD, UK.
Type
Published Article
Journal
Molecular Microbiology
Publisher
Wiley (Blackwell Publishing)
Publication Date
Dec 01, 2017
Volume
106
Issue
6
Pages
961–975
Identifiers
DOI: 10.1111/mmi.13861
PMID: 29030914
Source
Medline
License
Unknown

Abstract

Facultative phototrophs such as Rhodobacter sphaeroides can switch between heterotrophic and photosynthetic growth. This transition is governed by oxygen tension and involves the large-scale production of bacteriochlorophyll, which shares a biosynthetic pathway with haem up to protoporphyrin IX. Here, the pathways diverge with the insertion of Fe2+ or Mg2+ into protoporphyrin by ferrochelatase or magnesium chelatase, respectively. Tight regulation of this branchpoint is essential, but the mechanisms for switching between respiratory and photosynthetic growth are poorly understood. We show that PufQ governs the haem/bacteriochlorophyll switch; pufQ is found within the oxygen-regulated pufQBALMX operon encoding the reaction centre-light-harvesting photosystem complex. A pufQ deletion strain synthesises low levels of bacteriochlorophyll and accumulates the biosynthetic precursor coproporphyrinogen III; a suppressor mutant of this strain harbours a mutation in the hemH gene encoding ferrochelatase, substantially reducing ferrochelatase activity and increasing cellular bacteriochlorophyll levels. FLAG-immunoprecipitation experiments retrieve a ferrochelatase-PufQ-carotenoid complex, proposed to regulate the haem/bacteriochlorophyll branchpoint by directing porphyrin flux toward bacteriochlorophyll production under oxygen-limiting conditions. The co-location of pufQ and the photosystem genes in the same operon ensures that switching of tetrapyrrole metabolism toward bacteriochlorophyll is coordinated with the production of reaction centre and light-harvesting polypeptides.

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