Zam Is a Redox-Regulated Member of the RNB-Family Required for Optimal Photosynthesis in Cyanobacteria

The gene mediating resistance to acetazolamide in cyanobacteria was discovered thirty years ago during a drug tolerance screen. We use phylogenetics to show that Zam proteins are distributed across cyanobacteria and that they form their own unique clade of the ribonuclease II/R (RNB) family. Despite...

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Bibliographic Details
Published in:Microorganisms (Basel) 2022-05, Vol.10 (5), p.1055
Main Authors: Thomas, Patrick E, Gates, Colin, Campodonico-Burnett, William, Cameron, Jeffrey C
Format: Article
Language:English
Subjects:
Absorption spectroscopy
Acetazolamide
Antibiotics
Conserved sequence
Crystal structure
Cyanobacteria
Drug resistance
Drug tolerance
E coli
Enzymes
Gene deletion
Gene expression
Genomes
In vitro methods and tests
In vivo methods and tests
Low temperature
Mutation
Oxidation
Oxidation-reduction potential
Phenotypes
Photosynthesis
Photosystem II
phycobilisome
Phycocyanin
Phylogeny
Pigmentation
Plasmids
Prokaryotes
Proteins
reduction-oxidation
Residues
RNase
Room temperature
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Summary:The gene mediating resistance to acetazolamide in cyanobacteria was discovered thirty years ago during a drug tolerance screen. We use phylogenetics to show that Zam proteins are distributed across cyanobacteria and that they form their own unique clade of the ribonuclease II/R (RNB) family. Despite being RNB family members, multiple sequence alignments reveal that Zam proteins lack conservation and exhibit extreme degeneracy in the canonical active site-raising questions about their cellular function(s). Several known phenotypes arise from the deletion of , including drug resistance, slower growth, and altered pigmentation. Using room-temperature and low-temperature fluorescence and absorption spectroscopy, we show that deletion of results in decreased phycocyanin synthesis rates, altered PSI:PSII ratios, and an increase in coupling between the phycobilisome and PSII. Conserved cysteines within Zam are identified and assayed for function using in vitro and in vivo methods. We show that these cysteines are essential for Zam function, with mutation of either residue to serine causing phenotypes identical to the deletion of Zam. Redox regulation of Zam activity based on the reversible oxidation-reduction of a disulfide bond involving these cysteine residues could provide a mechanism to integrate the 'central dogma' with photosynthesis in cyanobacteria.
ISSN:2076-2607
2076-2607
DOI:10.3390/microorganisms10051055