7MH5

Crystal structure of R. sphaeroides Photosynthetic Reaction Center variant; Y(M210)3-iodotyrosine

Summary for 7MH5

• Entry DOI: 10.2210/pdb7mh5/pdb
• Descriptor: Reaction center protein H chain, CARDIOLIPIN, Reaction center protein L chain, ... (11 entities in total)
• Functional Keywords: photosynthetic, membrane protein, noncanonical amino acid, iodotyrosine, photosynthesis
• Biological source: Rhodobacter sphaeroides (Rhodopseudomonas sphaeroides); More
• Total number of polymer chains: 3
• Total formula weight: 105569.30

Authors

Mathews, I.,Weaver, J.,Boxer, S.G. (deposition date: 2021-04-14, release date: 2021-12-29)

Primary citation

Weaver, J.B.,Lin, C.Y.,Faries, K.M.,Mathews, I.I.,Russi, S.,Holten, D.,Kirmaier, C.,Boxer, S.G.
Photosynthetic reaction center variants made via genetic code expansion show Tyr at M210 tunes the initial electron transfer mechanism.
Proc.Natl.Acad.Sci.USA, 118:-, 2021

PubMed Abstract: Photosynthetic reaction centers (RCs) from were engineered to vary the electronic properties of a key tyrosine (M210) close to an essential electron transfer component via its replacement with site-specific, genetically encoded noncanonical amino acid tyrosine analogs. High fidelity of noncanonical amino acid incorporation was verified with mass spectrometry and X-ray crystallography and demonstrated that RC variants exhibit no significant structural alterations relative to wild type (WT). Ultrafast transient absorption spectroscopy indicates the excited primary electron donor, P*, decays via a ∼4-ps and a ∼20-ps population to produce the charge-separated state PH in all variants. Global analysis indicates that in the ∼4-ps population, PH forms through a two-step process, P*→ PB→ PH, while in the ∼20-ps population, it forms via a one-step P* → PH superexchange mechanism. The percentage of the P* population that decays via the superexchange route varies from ∼25 to ∼45% among variants, while in WT, this percentage is ∼15%. Increases in the P* population that decays via superexchange correlate with increases in the free energy of the PB intermediate caused by a given M210 tyrosine analog. This was experimentally estimated through resonance Stark spectroscopy, redox titrations, and near-infrared absorption measurements. As the most energetically perturbative variant, 3-nitrotyrosine at M210 creates an ∼110-meV increase in the free energy of PB along with a dramatic diminution of the 1,030-nm transient absorption band indicative of PB formation. Collectively, this work indicates the tyrosine at M210 tunes the mechanism of primary electron transfer in the RC.

PubMed: 34907018
DOI: 10.1073/pnas.2116439118

Experimental method

X-RAY DIFFRACTION (2.85 Å)