Charge-Transfer Processes within the Isolated Tetramer Models of the Reaction Center Rhodobacter sphaeroides

Area of Science:

• Photosynthesis research
• Structural biology
• Computational biophysics

Background:

• Photosystem (PS) supercomplexes are crucial for photosynthesis but remain complex to study.
• The Rhodobacter sphaeroides reaction center (RSRC) initiates charge separation (CS) via a charge-transfer (CT) step at the special pair (P).

Purpose of the Study:

• To computationally investigate charge transfer (CT) rectification mechanisms in the RSRC.
• To elucidate the factors influencing the directionality and rate of electron transfer in RSRC.

Main Methods:

• Employed a first-principles approach using an optimally tuned screened range-separated hybrid functional (SRSH).
• Utilized a polarizable continuum model (PCM) to simulate the protein environment.
• Calculated rate constants using Fermi's golden rule.

Main Results:

• Observed a significantly faster CT rate in the A branch compared to the B branch of the RSRC.
• Attributed the rate difference to the specific orientation of pigments near the special pair (P).
• Identified the influence of the surrounding protein complex on the local dielectric constant as a key factor.

Conclusions:

• The RSRC exhibits directional charge transfer, with the A branch facilitating faster electron transfer.
• Pigment arrangement and the protein microenvironment are critical determinants of CT efficiency in RSRC.
• This study provides a detailed computational insight into the mechanisms governing charge separation in photosynthetic reaction centers.