Contributions of the protein environment to the midpoint potentials of the A1 phylloquinones and the FX iron-sulfur cluster in photosystem I

Irina Karyagina, Yulia Pushkar, Dietmar Stehlik, Art Van Der Est, Hiroshi Ishikita, Ernst Walter Knapp, Bharat Jagannathan, Rufat Agalarov, John H. Golbeck

Research output: Contribution to journalArticle

16 Citations (Scopus)

Abstract

Electrostatic calculations have predicted that the partial negative charge associated with D575PsaB plays a significant role in modulating the midpoint potentials of the A1A and A1B phylloquinones in photosystem I. To test this prediction, the side chain of residue 575 PsaB was changed from negatively charged (D) to neutral (A) and to positively charged (K). D566PsaB, which is located at a considerable distance from either A1A or A1B, and should affect primarily the midpoint potential of FX, was similarly changed. In the 575PsaB variants, the rate of electron transfer from A1A to FX is observed to decrease slightly according to the sequence D/A/K. In the 566PsaB variants, the opposite effect of a slight increase in the rate is observed according to the same sequence D/A/K. These results are consistent with the expectation that changing these residues will shift the midpoint potentials of nearby cofactors to more positive values and that the magnitude of this shift will depend on the distance between the cofactors and the residues being changed. Thus, the midpoint potentials of A1A and A1B should experience a larger shift than will FX in the 575PsaB variants, while FX should experience a larger shift than will either A1A or A1B in the 566PsaB variants. As a result, the driving energy for electron transfer from A1A and A1B to FX will be decreased in the former and increased in the latter. This rationalization of the changes in kinetics is compared with the results of electrostatic calculations. While the altered amino acids shift the midpoint potentials of A1A, A1B, and FX by different amounts, the difference in the shifts between A1A and FX or between A1B and FX is small so that the overall effect on the electron transfer rate between A1A and FX or between A1B and F X is predicted to be small. These conclusions are borne out by experiment.

Original languageEnglish (US)
Pages (from-to)10804-10816
Number of pages13
JournalBiochemistry
Volume46
Issue number38
DOIs
StatePublished - Sep 25 2007

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Vitamin K 1
Photosystem I Protein Complex
Sulfur
Iron
Electrons
Static Electricity
Electrostatics
Proteins
Energy Transfer
Amino Acids
Kinetics
Experiments

All Science Journal Classification (ASJC) codes

  • Biochemistry

Cite this

Karyagina, Irina ; Pushkar, Yulia ; Stehlik, Dietmar ; Van Der Est, Art ; Ishikita, Hiroshi ; Knapp, Ernst Walter ; Jagannathan, Bharat ; Agalarov, Rufat ; Golbeck, John H. / Contributions of the protein environment to the midpoint potentials of the A1 phylloquinones and the FX iron-sulfur cluster in photosystem I. In: Biochemistry. 2007 ; Vol. 46, No. 38. pp. 10804-10816.
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title = "Contributions of the protein environment to the midpoint potentials of the A1 phylloquinones and the FX iron-sulfur cluster in photosystem I",
abstract = "Electrostatic calculations have predicted that the partial negative charge associated with D575PsaB plays a significant role in modulating the midpoint potentials of the A1A and A1B phylloquinones in photosystem I. To test this prediction, the side chain of residue 575 PsaB was changed from negatively charged (D) to neutral (A) and to positively charged (K). D566PsaB, which is located at a considerable distance from either A1A or A1B, and should affect primarily the midpoint potential of FX, was similarly changed. In the 575PsaB variants, the rate of electron transfer from A1A to FX is observed to decrease slightly according to the sequence D/A/K. In the 566PsaB variants, the opposite effect of a slight increase in the rate is observed according to the same sequence D/A/K. These results are consistent with the expectation that changing these residues will shift the midpoint potentials of nearby cofactors to more positive values and that the magnitude of this shift will depend on the distance between the cofactors and the residues being changed. Thus, the midpoint potentials of A1A and A1B should experience a larger shift than will FX in the 575PsaB variants, while FX should experience a larger shift than will either A1A or A1B in the 566PsaB variants. As a result, the driving energy for electron transfer from A1A and A1B to FX will be decreased in the former and increased in the latter. This rationalization of the changes in kinetics is compared with the results of electrostatic calculations. While the altered amino acids shift the midpoint potentials of A1A, A1B, and FX by different amounts, the difference in the shifts between A1A and FX or between A1B and FX is small so that the overall effect on the electron transfer rate between A1A and FX or between A1B and F X is predicted to be small. These conclusions are borne out by experiment.",
author = "Irina Karyagina and Yulia Pushkar and Dietmar Stehlik and {Van Der Est}, Art and Hiroshi Ishikita and Knapp, {Ernst Walter} and Bharat Jagannathan and Rufat Agalarov and Golbeck, {John H.}",
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Karyagina, I, Pushkar, Y, Stehlik, D, Van Der Est, A, Ishikita, H, Knapp, EW, Jagannathan, B, Agalarov, R & Golbeck, JH 2007, 'Contributions of the protein environment to the midpoint potentials of the A1 phylloquinones and the FX iron-sulfur cluster in photosystem I', Biochemistry, vol. 46, no. 38, pp. 10804-10816. https://doi.org/10.1021/bi700846z

Contributions of the protein environment to the midpoint potentials of the A1 phylloquinones and the FX iron-sulfur cluster in photosystem I. / Karyagina, Irina; Pushkar, Yulia; Stehlik, Dietmar; Van Der Est, Art; Ishikita, Hiroshi; Knapp, Ernst Walter; Jagannathan, Bharat; Agalarov, Rufat; Golbeck, John H.

In: Biochemistry, Vol. 46, No. 38, 25.09.2007, p. 10804-10816.

Research output: Contribution to journalArticle

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T1 - Contributions of the protein environment to the midpoint potentials of the A1 phylloquinones and the FX iron-sulfur cluster in photosystem I

AU - Karyagina, Irina

AU - Pushkar, Yulia

AU - Stehlik, Dietmar

AU - Van Der Est, Art

AU - Ishikita, Hiroshi

AU - Knapp, Ernst Walter

AU - Jagannathan, Bharat

AU - Agalarov, Rufat

AU - Golbeck, John H.

PY - 2007/9/25

Y1 - 2007/9/25

N2 - Electrostatic calculations have predicted that the partial negative charge associated with D575PsaB plays a significant role in modulating the midpoint potentials of the A1A and A1B phylloquinones in photosystem I. To test this prediction, the side chain of residue 575 PsaB was changed from negatively charged (D) to neutral (A) and to positively charged (K). D566PsaB, which is located at a considerable distance from either A1A or A1B, and should affect primarily the midpoint potential of FX, was similarly changed. In the 575PsaB variants, the rate of electron transfer from A1A to FX is observed to decrease slightly according to the sequence D/A/K. In the 566PsaB variants, the opposite effect of a slight increase in the rate is observed according to the same sequence D/A/K. These results are consistent with the expectation that changing these residues will shift the midpoint potentials of nearby cofactors to more positive values and that the magnitude of this shift will depend on the distance between the cofactors and the residues being changed. Thus, the midpoint potentials of A1A and A1B should experience a larger shift than will FX in the 575PsaB variants, while FX should experience a larger shift than will either A1A or A1B in the 566PsaB variants. As a result, the driving energy for electron transfer from A1A and A1B to FX will be decreased in the former and increased in the latter. This rationalization of the changes in kinetics is compared with the results of electrostatic calculations. While the altered amino acids shift the midpoint potentials of A1A, A1B, and FX by different amounts, the difference in the shifts between A1A and FX or between A1B and FX is small so that the overall effect on the electron transfer rate between A1A and FX or between A1B and F X is predicted to be small. These conclusions are borne out by experiment.

AB - Electrostatic calculations have predicted that the partial negative charge associated with D575PsaB plays a significant role in modulating the midpoint potentials of the A1A and A1B phylloquinones in photosystem I. To test this prediction, the side chain of residue 575 PsaB was changed from negatively charged (D) to neutral (A) and to positively charged (K). D566PsaB, which is located at a considerable distance from either A1A or A1B, and should affect primarily the midpoint potential of FX, was similarly changed. In the 575PsaB variants, the rate of electron transfer from A1A to FX is observed to decrease slightly according to the sequence D/A/K. In the 566PsaB variants, the opposite effect of a slight increase in the rate is observed according to the same sequence D/A/K. These results are consistent with the expectation that changing these residues will shift the midpoint potentials of nearby cofactors to more positive values and that the magnitude of this shift will depend on the distance between the cofactors and the residues being changed. Thus, the midpoint potentials of A1A and A1B should experience a larger shift than will FX in the 575PsaB variants, while FX should experience a larger shift than will either A1A or A1B in the 566PsaB variants. As a result, the driving energy for electron transfer from A1A and A1B to FX will be decreased in the former and increased in the latter. This rationalization of the changes in kinetics is compared with the results of electrostatic calculations. While the altered amino acids shift the midpoint potentials of A1A, A1B, and FX by different amounts, the difference in the shifts between A1A and FX or between A1B and FX is small so that the overall effect on the electron transfer rate between A1A and FX or between A1B and F X is predicted to be small. These conclusions are borne out by experiment.

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