Understanding of the binding interface between PsaC and the PsaA/PsaB heterodimer in photosystem I

Bharat Jagannathan, John H. Golbeck

Research output: Contribution to journalArticle

15 Citations (Scopus)

Abstract

The PsaC subunit of Photosystem I (PS I) is tightly bound to the PsaA/PsaB heterodimer via an extensive network of ionic and hydrogen bonds. To improve our understanding of the design of the PsaC-PsaA/PsaB binding interface, variants of PsaC were generated, each lacking a key binding contact with the PsaA/PsaB heterodimer. The characteristics of the reconstituted, variant PS I complexes were monitored by time-resolved optical spectroscopy, low-temperature EPR spectroscopy, and electron transfer throughput measurements. In the absence of the ionic bond forming contacts R52C or R65C, a markedly slower charge recombination occurs between P700+ and [FA/FB]-. The addition of PsaD leads to the restoration of native recombination kinetics in a fraction of the PS I complexes reconstituted with R52AC, but not with R65AC. Contrary to expectation, the absence of Y80C, which forms two symmetry-breaking H-bonds with PsaB, does not significantly affect the binding of PsaC as judged by the rate of charge recombination between P700+ and [FA/FB]-. However, the removal of the entire C-terminus results in a dramatic decrease in the rate of charge recombination. Low-temperature EPR spectra of the variant PS I complexes indicate that the magnetic environments of FA and FB are altered when compared to that of native PS I. The slowing of the rate of charge recombination in the variant PS I complexes could be due to an increase in the distance between FX and FA/FB as the result of non-native binding or to an altered reduction potential of the iron-sulfur clusters, which would result in a different rate of thermalization up the electron acceptor chain. The most significant finding is that the variant PS I complexes support lower rates of light-induced flavodoxin reduction and that the rates deteriorate rapidly on exposure to dioxygen due to the degradation of FA and FB. We suggest that the extensive set of ionic bonds and H-bonds between PsaC and the PsaA/PsaB heterodimer has evolved to ensure an exceedingly tight binding interface, thereby rendering the [4Fe-4S] clusters in PsaC inaccessible to dioxygen at the onset of oxygenic photosynthesis.

Original languageEnglish (US)
Pages (from-to)5405-5416
Number of pages12
JournalBiochemistry
Volume48
Issue number23
DOIs
StatePublished - Jun 16 2009

Fingerprint

Photosystem I Protein Complex
Genetic Recombination
Paramagnetic resonance
Spectrum Analysis
Flavodoxin
Electrons
Oxygen
Temperature
Photosynthesis
Sulfur
Restoration
Hydrogen
Hydrogen bonds
Iron
Throughput
Spectroscopy
Light
Degradation
Kinetics

All Science Journal Classification (ASJC) codes

  • Biochemistry

Cite this

@article{f98b2950201d47869f8bac01797aa84e,
title = "Understanding of the binding interface between PsaC and the PsaA/PsaB heterodimer in photosystem I",
abstract = "The PsaC subunit of Photosystem I (PS I) is tightly bound to the PsaA/PsaB heterodimer via an extensive network of ionic and hydrogen bonds. To improve our understanding of the design of the PsaC-PsaA/PsaB binding interface, variants of PsaC were generated, each lacking a key binding contact with the PsaA/PsaB heterodimer. The characteristics of the reconstituted, variant PS I complexes were monitored by time-resolved optical spectroscopy, low-temperature EPR spectroscopy, and electron transfer throughput measurements. In the absence of the ionic bond forming contacts R52C or R65C, a markedly slower charge recombination occurs between P700+ and [FA/FB]-. The addition of PsaD leads to the restoration of native recombination kinetics in a fraction of the PS I complexes reconstituted with R52AC, but not with R65AC. Contrary to expectation, the absence of Y80C, which forms two symmetry-breaking H-bonds with PsaB, does not significantly affect the binding of PsaC as judged by the rate of charge recombination between P700+ and [FA/FB]-. However, the removal of the entire C-terminus results in a dramatic decrease in the rate of charge recombination. Low-temperature EPR spectra of the variant PS I complexes indicate that the magnetic environments of FA and FB are altered when compared to that of native PS I. The slowing of the rate of charge recombination in the variant PS I complexes could be due to an increase in the distance between FX and FA/FB as the result of non-native binding or to an altered reduction potential of the iron-sulfur clusters, which would result in a different rate of thermalization up the electron acceptor chain. The most significant finding is that the variant PS I complexes support lower rates of light-induced flavodoxin reduction and that the rates deteriorate rapidly on exposure to dioxygen due to the degradation of FA and FB. We suggest that the extensive set of ionic bonds and H-bonds between PsaC and the PsaA/PsaB heterodimer has evolved to ensure an exceedingly tight binding interface, thereby rendering the [4Fe-4S] clusters in PsaC inaccessible to dioxygen at the onset of oxygenic photosynthesis.",
author = "Bharat Jagannathan and Golbeck, {John H.}",
year = "2009",
month = "6",
day = "16",
doi = "10.1021/bi900243f",
language = "English (US)",
volume = "48",
pages = "5405--5416",
journal = "Biochemistry",
issn = "0006-2960",
publisher = "American Chemical Society",
number = "23",

}

Understanding of the binding interface between PsaC and the PsaA/PsaB heterodimer in photosystem I. / Jagannathan, Bharat; Golbeck, John H.

In: Biochemistry, Vol. 48, No. 23, 16.06.2009, p. 5405-5416.

Research output: Contribution to journalArticle

TY - JOUR

T1 - Understanding of the binding interface between PsaC and the PsaA/PsaB heterodimer in photosystem I

AU - Jagannathan, Bharat

AU - Golbeck, John H.

PY - 2009/6/16

Y1 - 2009/6/16

N2 - The PsaC subunit of Photosystem I (PS I) is tightly bound to the PsaA/PsaB heterodimer via an extensive network of ionic and hydrogen bonds. To improve our understanding of the design of the PsaC-PsaA/PsaB binding interface, variants of PsaC were generated, each lacking a key binding contact with the PsaA/PsaB heterodimer. The characteristics of the reconstituted, variant PS I complexes were monitored by time-resolved optical spectroscopy, low-temperature EPR spectroscopy, and electron transfer throughput measurements. In the absence of the ionic bond forming contacts R52C or R65C, a markedly slower charge recombination occurs between P700+ and [FA/FB]-. The addition of PsaD leads to the restoration of native recombination kinetics in a fraction of the PS I complexes reconstituted with R52AC, but not with R65AC. Contrary to expectation, the absence of Y80C, which forms two symmetry-breaking H-bonds with PsaB, does not significantly affect the binding of PsaC as judged by the rate of charge recombination between P700+ and [FA/FB]-. However, the removal of the entire C-terminus results in a dramatic decrease in the rate of charge recombination. Low-temperature EPR spectra of the variant PS I complexes indicate that the magnetic environments of FA and FB are altered when compared to that of native PS I. The slowing of the rate of charge recombination in the variant PS I complexes could be due to an increase in the distance between FX and FA/FB as the result of non-native binding or to an altered reduction potential of the iron-sulfur clusters, which would result in a different rate of thermalization up the electron acceptor chain. The most significant finding is that the variant PS I complexes support lower rates of light-induced flavodoxin reduction and that the rates deteriorate rapidly on exposure to dioxygen due to the degradation of FA and FB. We suggest that the extensive set of ionic bonds and H-bonds between PsaC and the PsaA/PsaB heterodimer has evolved to ensure an exceedingly tight binding interface, thereby rendering the [4Fe-4S] clusters in PsaC inaccessible to dioxygen at the onset of oxygenic photosynthesis.

AB - The PsaC subunit of Photosystem I (PS I) is tightly bound to the PsaA/PsaB heterodimer via an extensive network of ionic and hydrogen bonds. To improve our understanding of the design of the PsaC-PsaA/PsaB binding interface, variants of PsaC were generated, each lacking a key binding contact with the PsaA/PsaB heterodimer. The characteristics of the reconstituted, variant PS I complexes were monitored by time-resolved optical spectroscopy, low-temperature EPR spectroscopy, and electron transfer throughput measurements. In the absence of the ionic bond forming contacts R52C or R65C, a markedly slower charge recombination occurs between P700+ and [FA/FB]-. The addition of PsaD leads to the restoration of native recombination kinetics in a fraction of the PS I complexes reconstituted with R52AC, but not with R65AC. Contrary to expectation, the absence of Y80C, which forms two symmetry-breaking H-bonds with PsaB, does not significantly affect the binding of PsaC as judged by the rate of charge recombination between P700+ and [FA/FB]-. However, the removal of the entire C-terminus results in a dramatic decrease in the rate of charge recombination. Low-temperature EPR spectra of the variant PS I complexes indicate that the magnetic environments of FA and FB are altered when compared to that of native PS I. The slowing of the rate of charge recombination in the variant PS I complexes could be due to an increase in the distance between FX and FA/FB as the result of non-native binding or to an altered reduction potential of the iron-sulfur clusters, which would result in a different rate of thermalization up the electron acceptor chain. The most significant finding is that the variant PS I complexes support lower rates of light-induced flavodoxin reduction and that the rates deteriorate rapidly on exposure to dioxygen due to the degradation of FA and FB. We suggest that the extensive set of ionic bonds and H-bonds between PsaC and the PsaA/PsaB heterodimer has evolved to ensure an exceedingly tight binding interface, thereby rendering the [4Fe-4S] clusters in PsaC inaccessible to dioxygen at the onset of oxygenic photosynthesis.

UR - http://www.scopus.com/inward/record.url?scp=67049146502&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=67049146502&partnerID=8YFLogxK

U2 - 10.1021/bi900243f

DO - 10.1021/bi900243f

M3 - Article

C2 - 19432395

AN - SCOPUS:67049146502

VL - 48

SP - 5405

EP - 5416

JO - Biochemistry

JF - Biochemistry

SN - 0006-2960

IS - 23

ER -