Conserved residue PsaB-Trp673 is essential for high-efficiency electron transfer between the phylloquinones and the iron-sulfur clusters in Photosystem I

Vasily Kurashov, George Milanovsky, Lujun Luo, Antoine Martin, Alexey Yu Semenov, Sergei Savikhin, Dmitry A. Cherepanov, John H. Golbeck, Wu Xu

Research output: Contribution to journalArticlepeer-review

Abstract

Despite the high level of symmetry between the PsaA and PsaB polypeptides in Photosystem I, some amino acids pairs are strikingly different, such as PsaA-Gly693 and PsaB-Trp673, which are located near a cluster of 11 water molecules between the A1A and A1B quinones and the FX iron-sulfur cluster. In this work, we changed PsaB-Trp673 to PsaB-Phe673 in Synechocystis sp. PCC 6803. The variant contains ~ 85% of wild-type (WT) levels of Photosystem I but is unable to grow photoautotrophically. Both time-resolved and steady-state optical measurements show that in the PsaB-W673F variant less than 50% of the electrons reach the terminal iron-sulfur clusters FA and FB; the majority of the electrons recombine from A1A and A1B. However, in those reaction centers which pass electrons forward the transfer is heterogeneous: a minor population shows electron transfer rates from A1A and A1B to FX slightly slower than that of the WT, whereas a major population shows forward electron transfer rates to FX slowed to the ~ 10 µs time range. Competition between relatively similar forward and backward rates of electron transfer from the quinones to the FX cluster account for the relatively low yield of long-lived charge separation in the PsaB-W673F variant. A higher water content and its increased mobility observed in MD simulations in the interquinone cavity of the PsaB-W673F variant shifts the pK of PsaB-Asp575 and allows its deprotonation in situ. The heterogeneity found may be rooted in protonation state of PsaB-Asp575, which controls whether electron transfer can proceed beyond the phylloquinone cofactors.

Original languageEnglish (US)
Pages (from-to)161-180
Number of pages20
JournalPhotosynthesis research
Volume148
Issue number3
DOIs
StatePublished - Jun 2021

All Science Journal Classification (ASJC) codes

  • Biochemistry
  • Plant Science
  • Cell Biology

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