The protein environment of the bacteriopheophytin anion modulates charge separation and charge recombination in bacterial reaction centers

Jie Pan, Rafael G. Saer, Su Lin, Zhi Guo, J. Thomas Beatty, Neal Woodbury

Research output: Contribution to journalArticle

10 Citations (Scopus)

Abstract

The kinetics and pathway of electron transfer has been explored in a series of reaction center mutants from Rhodobacter sphaeroides, in which the leucine residue at M214 near the bacteriopheophytin cofactor in the A-branch has been replaced with methionine, cysteine, alanine, and glycine. These amino acids have substantially different volumes, both from each other and, except for methionine, from the native leucine. Though the mutation site of M214 is close to the bacteriopheophytin cofactor, which is involved in the electron transfer, none of the mutations alter the cofactor composition of the reaction center and the primary charge separation reaction is essentially undisturbed. However, the kinetics of electron transfer from HA - → Q A becomes both slower and substantially heterogeneous in three of the four mutants. The decreased HA - → QA electron transfer rate allows charge recombination between P+ and HA - to compete with the forward reaction, resulting in a drop in the overall yield of charge separation. Both the yield change and the variation in kinetics correlate well with the volume of the mutant amino acid side chains. Analysis of the kinetics suggests that the introduction of a smaller side chain at M214 results in greater protein structural heterogeneity and dynamics on multiple time scales, resulting in perturbation of the electronic environment and its evolution in the vicinity of the early charge-separated radical pair, P+HA -, and the subsequent acceptor QA, affecting both the extent and time scale of dielectric relaxation. It appears that the reaction center has been optimized not only in terms of its static structure-function relationships, but also finely tuned to favor particular reaction pathways on particular time scales by adjusting protein dynamics.

Original languageEnglish (US)
Pages (from-to)7179-7189
Number of pages11
JournalJournal of Physical Chemistry B
Volume117
Issue number24
DOIs
StatePublished - Jun 20 2013

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polarization (charge separation)
Anions
Negative ions
anions
proteins
Proteins
Amino acids
Kinetics
Electrons
electron transfer
Leucine
Methionine
methionine
leucine
kinetics
mutations
Amino Acids
amino acids
Dielectric relaxation
Alanine

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Materials Chemistry
  • Surfaces, Coatings and Films

Cite this

The protein environment of the bacteriopheophytin anion modulates charge separation and charge recombination in bacterial reaction centers. / Pan, Jie; Saer, Rafael G.; Lin, Su; Guo, Zhi; Beatty, J. Thomas; Woodbury, Neal.

In: Journal of Physical Chemistry B, Vol. 117, No. 24, 20.06.2013, p. 7179-7189.

Research output: Contribution to journalArticle

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