Mutations in algal and cyanobacterial Photosystem I that independently affect the yield of initial charge separation in the two electron transfer cofactor branches

Syed Lal Badshah, Junlei Sun, Sam Mula, Mike Gorka, Patricia Baker, Rajiv Luthra, Su Lin, Art van der Est, John H. Golbeck, Kevin E. Redding

Research output: Contribution to journalArticle

Abstract

In Photosystem I, light-induced electron transfer can occur in either of two symmetry-related branches of cofactors, each of which is composed of a pair of chlorophylls (ec2A/ec3A or ec2B/ec3B) and a phylloquinone (PhQA or PhQB). The axial ligand to the central Mg2 + of the ec2A and ec2B chlorophylls is a water molecule that is also H-bonded to a nearby Asn residue. Here, we investigate the importance of this interaction for charge separation by converting each of the Asn residues to a Leu in the green alga, Chlamydomonas reinhardtii, and the cyanobacterium, Synechocystis sp. PCC6803, and studying the energy and electron transfer using time-resolved optical and EPR spectroscopy. Nanosecond transient absorbance measurements of the PhQ to FX electron transfer show that in both species, the PsaA-N604L mutation (near ec2B) results in a ~ 50% reduction in the amount of electron transfer in the B-branch, while the PsaB-N591L mutation (near ec2A) results in a ~ 70% reduction in the amount of electron transfer in the A-branch. A diminished quantum yield of P700+ PhQ is also observed in ultrafast optical experiments, but the lower yield does not appear to be a consequence of charge recombination in the nanosecond or microsecond timescales. The most significant finding is that the yield of electron transfer in the unaffected branch did not increase to compensate for the lower yield in the affected branch. Hence, each branch of the reaction center appears to operate independently of the other in carrying out light-induced charge separation.

LanguageEnglish (US)
Pages42-55
Number of pages14
JournalBiochimica et Biophysica Acta - Bioenergetics
Volume1859
Issue number1
DOIs
StatePublished - Jan 1 2018

Fingerprint

Photosystem I Protein Complex
Electrons
Mutation
Chlorophyll
Vitamin K 1
Synechocystis
Light
Chlamydomonas reinhardtii
Chlorophyta
Energy Transfer
Cyanobacteria
Quantum yield
Algae
Genetic Recombination
Paramagnetic resonance
Spectrum Analysis
Spectroscopy
Ligands
Molecules
Water

Keywords

  • Electron transfer
  • Photosynthesis
  • Photosystem I
  • Primary charge separation
  • Quantum yield

ASJC Scopus subject areas

  • Biophysics
  • Biochemistry
  • Cell Biology

Cite this

Mutations in algal and cyanobacterial Photosystem I that independently affect the yield of initial charge separation in the two electron transfer cofactor branches. / Badshah, Syed Lal; Sun, Junlei; Mula, Sam; Gorka, Mike; Baker, Patricia; Luthra, Rajiv; Lin, Su; van der Est, Art; Golbeck, John H.; Redding, Kevin E.

In: Biochimica et Biophysica Acta - Bioenergetics, Vol. 1859, No. 1, 01.01.2018, p. 42-55.

Research output: Contribution to journalArticle

Badshah, Syed Lal ; Sun, Junlei ; Mula, Sam ; Gorka, Mike ; Baker, Patricia ; Luthra, Rajiv ; Lin, Su ; van der Est, Art ; Golbeck, John H. ; Redding, Kevin E./ Mutations in algal and cyanobacterial Photosystem I that independently affect the yield of initial charge separation in the two electron transfer cofactor branches. In: Biochimica et Biophysica Acta - Bioenergetics. 2018 ; Vol. 1859, No. 1. pp. 42-55
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T1 - Mutations in algal and cyanobacterial Photosystem I that independently affect the yield of initial charge separation in the two electron transfer cofactor branches

AU - Badshah,Syed Lal

AU - Sun,Junlei

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AU - Gorka,Mike

AU - Baker,Patricia

AU - Luthra,Rajiv

AU - Lin,Su

AU - van der Est,Art

AU - Golbeck,John H.

AU - Redding,Kevin E.

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AB - In Photosystem I, light-induced electron transfer can occur in either of two symmetry-related branches of cofactors, each of which is composed of a pair of chlorophylls (ec2A/ec3A or ec2B/ec3B) and a phylloquinone (PhQA or PhQB). The axial ligand to the central Mg2 + of the ec2A and ec2B chlorophylls is a water molecule that is also H-bonded to a nearby Asn residue. Here, we investigate the importance of this interaction for charge separation by converting each of the Asn residues to a Leu in the green alga, Chlamydomonas reinhardtii, and the cyanobacterium, Synechocystis sp. PCC6803, and studying the energy and electron transfer using time-resolved optical and EPR spectroscopy. Nanosecond transient absorbance measurements of the PhQ to FX electron transfer show that in both species, the PsaA-N604L mutation (near ec2B) results in a ~ 50% reduction in the amount of electron transfer in the B-branch, while the PsaB-N591L mutation (near ec2A) results in a ~ 70% reduction in the amount of electron transfer in the A-branch. A diminished quantum yield of P700+ PhQ− is also observed in ultrafast optical experiments, but the lower yield does not appear to be a consequence of charge recombination in the nanosecond or microsecond timescales. The most significant finding is that the yield of electron transfer in the unaffected branch did not increase to compensate for the lower yield in the affected branch. Hence, each branch of the reaction center appears to operate independently of the other in carrying out light-induced charge separation.

KW - Electron transfer

KW - Photosynthesis

KW - Photosystem I

KW - Primary charge separation

KW - Quantum yield

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