Many Combinations of Amino Acid Sequences in a Conserved Region of the D1 Protein Satisfy Photosystem II Function

Hadar Kless, Willem Vermaas

Research output: Contribution to journalArticle

20 Citations (Scopus)

Abstract

The putativedehelix of the D1 protein is located at the acceptor side of photosystem II (PS II) and serves as an indispensable part of a niche that binds the secondary plastoquinone QB. Combinatorial mutagenesis was applied to a stretch of four residues in a highy conserved region of this putative helix in order to reveal amino acid combinations that are able to support PS II function. An obligate photoheterotrophic mutant of the cyanobacteriumSynechocystiss o. PCC 6803, missing four residues (ΔYFGR254-7in thedehelix, was transformed with a D1-coding sequence carrying fully degenerate combinations of codons at the site of the deletion. Upon selection for photoautotrophy, 25 mutants with functional PS II were isolated. All mutants showed different codon combinations at positions 254 to 257; none was identical to the wild-type sequence, and none of the conserved residues was found to be mandatory for PS II function. However, 24 of the mutants contained Tyr or Phe at position 254 while at the other three positions many different amino acid combinations could be functionally accommodated. Most sequences maintained an amphiphilic arrangement of the helix that may align Tyr254 facing the lQBbinding pocket. This residue is proposed to be functionall y analogous to Phe216 of the L subunit in purple bacteria which contributes to binding of QB. Most of the PS II properties were similar in the mutants compared to wild-type. Noticeable modifications in the mutants concerned the semiquinone equilibrium of electron transfer between QAand QB, and the affinity of PS II inhibitors. Differential effects on the semiquinone equilibrium were observed between two distinct quinones occupying the QBsite (plastoquinoneversus2,5-dichloro-p-benzo-quinone), implying that residues in this domain are involved, directly or indirectly, with different binding determinants of the quinones. Even though many different combinations of amino acids in positions 254 to 257 of the D1 protein may satisfy the primary function of PS II, complex requirements need to be combined for optimized performance of the QBbinding niche.

Original languageEnglish (US)
Pages (from-to)120-131
Number of pages12
JournalJournal of Molecular Biology
Volume246
Issue number1
DOIs
StatePublished - Feb 10 1995

Fingerprint

Photosystem II Protein Complex
Amino Acid Sequence
Proteins
Quinones
Amino Acids
Codon
Plastoquinone
Proteobacteria
Conserved Sequence
Mutagenesis
Electrons

Keywords

  • combinatorial mutagenesis
  • cyanobacteria
  • molecular evolution
  • protein-cofactor interaction
  • reaction center

ASJC Scopus subject areas

  • Molecular Biology
  • Virology

Cite this

Many Combinations of Amino Acid Sequences in a Conserved Region of the D1 Protein Satisfy Photosystem II Function. / Kless, Hadar; Vermaas, Willem.

In: Journal of Molecular Biology, Vol. 246, No. 1, 10.02.1995, p. 120-131.

Research output: Contribution to journalArticle

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abstract = "The putativedehelix of the D1 protein is located at the acceptor side of photosystem II (PS II) and serves as an indispensable part of a niche that binds the secondary plastoquinone QB. Combinatorial mutagenesis was applied to a stretch of four residues in a highy conserved region of this putative helix in order to reveal amino acid combinations that are able to support PS II function. An obligate photoheterotrophic mutant of the cyanobacteriumSynechocystiss o. PCC 6803, missing four residues (ΔYFGR254-7in thedehelix, was transformed with a D1-coding sequence carrying fully degenerate combinations of codons at the site of the deletion. Upon selection for photoautotrophy, 25 mutants with functional PS II were isolated. All mutants showed different codon combinations at positions 254 to 257; none was identical to the wild-type sequence, and none of the conserved residues was found to be mandatory for PS II function. However, 24 of the mutants contained Tyr or Phe at position 254 while at the other three positions many different amino acid combinations could be functionally accommodated. Most sequences maintained an amphiphilic arrangement of the helix that may align Tyr254 facing the lQBbinding pocket. This residue is proposed to be functionall y analogous to Phe216 of the L subunit in purple bacteria which contributes to binding of QB. Most of the PS II properties were similar in the mutants compared to wild-type. Noticeable modifications in the mutants concerned the semiquinone equilibrium of electron transfer between QAand QB, and the affinity of PS II inhibitors. Differential effects on the semiquinone equilibrium were observed between two distinct quinones occupying the QBsite (plastoquinoneversus2,5-dichloro-p-benzo-quinone), implying that residues in this domain are involved, directly or indirectly, with different binding determinants of the quinones. Even though many different combinations of amino acids in positions 254 to 257 of the D1 protein may satisfy the primary function of PS II, complex requirements need to be combined for optimized performance of the QBbinding niche.",
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