Abstract
Members of the light-harvesting complex protein family participate in multiple processes connected with light sensing, light absorption, and pigment binding within the thylakoid membrane. Amino acid residues of the light-harvesting chlorophyll a/b-binding proteins involved in pigment binding have been precisely identified through x-ray crystallography experiments. In vitro pigment-binding studies have been performed with LIGHT-HARVESTING-LIKE3 proteins, and the pigment-binding ability of cyanobacterial high-light-inducible proteins has been studied in detail. However, analysis of pigment binding by plant high-light-inducible protein homologs, called ONE-HELIX PROTEINS (OHPs), is lacking. Here, we report on successful in vitro reconstitution of Arabidopsis (Arabidopsis thaliana) OHPs with chlorophylls and carotenoids and show that pigment binding depends on the formation of OHP1/OHP2 heterodimers. Pigment-binding capacity was completely lost in each of the OHPs when residues of the light-harvesting complex chlorophyll-binding motif required for chlorophyll binding were mutated. Moreover, the mutated OHP variants failed to rescue the respective knockout (T-DNA insertion) mutants, indicating that pigment-binding ability is essential for OHP function in vivo. The scaffold protein HIGH CHLOROPHYLL FLUORESCENCE244 (HCF244) is tethered to the thylakoid membrane by the OHP heterodimer. We show that HCF244 stability depends on OHP heterodimer formation and introduce the concept of a functional unit consisting of OHP1, OHP2, and HCF244, in which each protein requires the others. Because of their pigment-binding capacity, we suggest that OHPs function in the delivery of pigments to the D1 subunit of PSII.
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Claims 6
Claim · model-written summary
In vitro reconstitution of Arabidopsis OHPs with chlorophylls and carotenoids succeeded.
- Taxon
- Arabidopsis thaliana
Arabidopsis thalianae0 - Outcome
- successful in vitro reconstitutione0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“we report on successful in vitro reconstitution of Arabidopsis (Arabidopsis thaliana) OHPs with chlorophylls and carotenoids”
Claim · model-written summary
Pigment binding depends on the formation of OHP1/OHP2 heterodimers.
- Taxon
- Arabidopsis thalianaArabidopsis thalianae0
- Gene
- OHP1/OHP2 heterodimerse1
- Outcome
- pigment bindinge1
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“we report on successful in vitro reconstitution of Arabidopsis (Arabidopsis thaliana) OHPs”
e1“show that pigment binding depends on the formation of OHP1/OHP2 heterodimers”
Claim · model-written summary
Pigment-binding capacity of each OHP was completely lost when chlorophyll-binding motif residues were mutated.
- Taxon
- Arabidopsis thalianaArabidopsis thalianae0
- Treatment
- residues of the light-harvesting complex chlorophyll-binding motife2
- Outcome
- Pigment-binding capacitye2
- Direction
- completely loste2
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“we report on successful in vitro reconstitution of Arabidopsis (Arabidopsis thaliana) OHPs”
e2“Pigment-binding capacity was completely lost in each of the OHPs when residues of the light-harvesting complex chlorophyll-binding motif required for chlorophyll binding were mutated”
Claim · model-written summary
Mutated OHP variants failed to rescue the knockout mutants, indicating that pigment-binding ability is essential for OHP function in vivo.
- Taxon
- Arabidopsis thalianaArabidopsis thalianae0
- Treatment
- mutated OHP variantse3
- Outcome
- rescuee3
- Direction
- failed to rescuee3
- Qualifier
- pigment-binding ability is essential for OHP function in vivoe3
- Comparator
- knockout (T-DNA insertion) mutantse3
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“we report on successful in vitro reconstitution of Arabidopsis (Arabidopsis thaliana) OHPs”
e3“the mutated OHP variants failed to rescue the respective knockout (T-DNA insertion) mutants, indicating that pigment-binding ability is essential for OHP function in vivo”
Claim · model-written summary
HCF244 stability depends on OHP heterodimer formation.
- Taxon
- Arabidopsis thalianaArabidopsis thalianae0
- Gene
- HCF244e4
- Outcome
- HCF244 stabilitye4
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“we report on successful in vitro reconstitution of Arabidopsis (Arabidopsis thaliana) OHPs”
e4“We show that HCF244 stability depends on OHP heterodimer formation”
Claim · model-written summary
OHPs are suggested to function in the delivery of pigments to the D1 subunit of PSII.
- Taxon
- Arabidopsis thalianaArabidopsis thalianae0
- Gene
- OHPse5
- Outcome
- delivery of pigments to the D1 subunit of PSIIe5
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Arabidopsis (Arabidopsis thaliana) OHPs”
e5“Because of their pigment-binding capacity, we suggest that OHPs function in the delivery of pigments to the D1 subunit of PSII”
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