skip to main content
US FlagAn official website of the United States government
dot gov icon
Official websites use .gov
A .gov website belongs to an official government organization in the United States.
https lock icon
Secure .gov websites use HTTPS
A lock ( lock ) or https:// means you've safely connected to the .gov website. Share sensitive information only on official, secure websites.

Explore Research Products in the PAR
It may take a few hours for recently added research products to appear in PAR search results.


Title: Shedding Light on Primary Donors in Photosynthetic Reaction Centers
Chlorophylls (Chl)s exist in a variety of flavors and are ubiquitous in both the energy and electron transfer processes of photosynthesis. The functions they perform often occur on the ultrafast (fs–ns) time scale and until recently, these have been difficult to measure in real time. Further, the complexity of the binding pockets and the resulting protein-matrix effects that alter the respective electronic properties have rendered theoretical modeling of these states difficult. Recent advances in experimental methodology, computational modeling, and emergence of new reaction center (RC) structures have renewed interest in these processes and allowed researchers to elucidate previously ambiguous functions of Chls and related pheophytins. This is complemented by a wealth of experimental data obtained from decades of prior research. Studying the electronic properties of Chl molecules has advanced our understanding of both the nature of the primary charge separation and subsequent electron transfer processes of RCs. In this review, we examine the structures of primary electron donors in Type I and Type II RCs in relation to the vast body of spectroscopic research that has been performed on them to date. Further, we present density functional theory calculations on each oxidized primary donor to study both their electronic properties and our ability to model experimental spectroscopic data. This allows us to directly compare the electronic properties of hetero- and homodimeric RCs.  more » « less
Award ID(s):
1852309
PAR ID:
10463499
Author(s) / Creator(s):
; ; ; ; ;
Date Published:
Journal Name:
Frontiers in Microbiology
Volume:
12
ISSN:
1664-302X
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. ; ; ; ; ; ; ; (, Advances in photosynthesis)
    H. J. M. Hou and S. I. Allakhverdiev (Ed.)
    Photosynthetic Reaction Centers (RCs) can be considered blueprints for highly efficient energy transfer. Embedded with an array of cofactors, including (bacterio)chlorophyll ((B)Chl) and (B)pheophytin ((B)Pheo) molecules, RCs function with a high quantum yield that spans a wide spectral range. Understanding the principles that underlie their function can influence the design of the next generation of artificial photosynthetic devices. We are particularly interested in the factors that influence the early stages of light-driven charge separation in RCs. With the recent publication of several highly anticipated RC structures and advanced computational methods available, it is possible to probe both the geometric and electronic structures of an array of RCs. In this chapter, we review the electronic and geometric structures of the (B)Chl and (B)Pheo primary electron acceptors from five RCs, comprising both Type I and Type II RCs and representing both heterodimeric and homodimeric systems. We showcase the dimeric A0●– state of Type I RCs, whereby the unpaired electron is delocalized, to various extents, over two (B)Chl molecules, (B)Chl2 and (B)Chl3. This delocalization is controlled by several factors, including the structure of the (B)Chls, interactions with the surrounding protein matrix, and the orientation and distances of the cofactors themselves. In contrast, the primary acceptors of Type II RCs are entirely monomeric, with electron density residing solely on the (B)Pheo. We compare the natural design of the primary acceptors of the Type I and Type II RCs from both an evolutionary and application based perspective. 
    more » « less
  2. ; ; ; ; ; ; ; ; (, Inorganic Chemistry)
    Type 1 copper (T1Cu) proteins play important roles in electron transfer in biology, largely due to the unique structure of the T1Cu center, which is reflected by its spectroscopic properties. Previous reports have suggested a correlation between a high ratio of electronic absorbance at ∼450 nm to that at ∼600 nm (R = A450/A600) and a large copper(II) hyperfine coupling in the z direction (Az) in electron paramagnetic resonance (EPR). However, this correlation does not have a clear physical meaning, nor does it hold for many proteins with a perturbed T1Cu center. To address this issue, a new parameter of R′ [A450/(A450 + A600)] with a better physical meaning of a fractional SCys pseudo-σ to Cu(II) charge transfer transition intensity is defined and a quadratic relationship between R′ and Az is found on the basis of a comprehensive analysis of ultraviolet–visible absorption, EPR, and structural parameters of T1Cu proteins. We are able to find good correlations between R′ and the displacement of copper from the trigonal plane defined by the His2Cys ligands and the angle between the NHis1–Cu–NHis2 plane and the SCys–Cu–axial ligand plane, providing a structural basis for the observed correlation. These findings and analyses provide a new framework for a deeper understanding of the spectroscopic and electronic properties of T1Cu proteins, which may allow better design and applications of this important class of proteins for redox and electron transfer functions. 
    more » « less
  3. ; ; ; ; ; (, Photochem)
    Chemically identical chlorophyll (Chl) molecules undergo conformational changes when they are embedded in a protein matrix. The conformational changes will modulate their absorption spectra to meet the need for programmed excitation energy transfer or electron transfer. To interpret spectroscopic data using the knowledge of pigment–protein interactions requires a single pigment embedded in one polypeptide matrix. Unfortunately, most of the known photosynthetic systems contain a set of multiple pigments in each protein subunit. This makes it complicated to interpret spectroscopic data using structural data due to the potential overlapping spectra of two or more pigments. Chl–protein interactions have not been systematically studied to answer three fundamental questions: (i) What are the structural characteristics and commonly shared substructures of different types of Chl molecules (e.g., Chl a, b, c, d, and f)? (ii) How many structural groups can Chl molecules be divided into and how are different structural groups influenced by their surrounding environments? (iii) What are the structural characteristics of pigment surrounding environments? Having no clear answers to the unresolved questions is probably due to a lack of computational methods for quantifying conformational changes in individual Chls and individual surrounding amino acids. The first version of the Triangular Spatial Relationship (TSR)-based method was developed for comparing protein 3D structures. The input data for the TSR-based method are experimentally determined 3D structures from the Protein Data Bank (PDB). In this study, we take advantage of the 3D structures of Chl-binding proteins deposited in the PDB and the TSR-based method to systematically investigate the 3D structures of various types of Chls and their protein environments. The key contributions of this study can be summarized as follows: (i) Specific structural characteristics of Chl d and f were identified and are defined using the TSR keys. (ii) Two and three clusters were found for various types of Chls and Chls a, respectively. The signature structures for distinguishing their corresponding two and three clusters were identified. (iii) Histidine residues were used as an example for revealing structural characteristics of Chl-binding sites. This study provides evidence for the three unresolved questions and builds a structural foundation through quantifying Chl conformations as well as structures of their embedded protein environments for future mechanistic understanding of relationships between Chl–protein interactions and their corresponding spectroscopic data. 
    more » « less
  4. ; ; ; ; (, Journal of Computational Chemistry)
    Abstract Time‐dependent density functional theory (TDDFT) was applied to gain insights into the electronic and vibrational spectroscopic properties of an important electron transport mediator, methyl viologen (MV2+). An organic dication, MV2+has numerous applications in electrochemistry that include energy conversion and storage, environmental remediation, and chemical sensing and electrosynthesis. MV2+is easily reduced by a single electron transfer to form a radical cation species (MV•+), which has an intense UV–visible absorption near 600 nm. The redox properties of the MV2+/MV•+couple and light‐sensitivity of MV•+have made the system appealing for photo‐electrochemical energy conversion (e.g., solar hydrogen generation from water) and the study of photo‐induced charge transfer processes through electronic absorption and resonance Raman spectroscopic measurements. The reported work applies leading TDDFT approaches to investigate the electronic and vibrational spectroscopic properties of MV2+and MV•+. Using a conventional hybrid exchange functional (B3‐LYP) and a long‐range corrected hybrid exchange functional (ωB97X‐D3), including with a conductor‐like polarizable continuum model to account for solvation, the electronic absorption and resonance Raman spectra predicted are in good agreement with experiment. Also analyzed are the charge transfer character and natural transition orbitals derived from the TDDFT vertical excitations calculated. The findings and models developed further the understanding of the electronic properties of viologens and related organic redox mediators important in renewable energy applications and serve as a reference for guiding the interpretation of electronic absorption and Raman spectra of the ions. 
    more » « less
  5. ; ; ; ; ; ; (, Materials Advances)
    Melanins have complex structures, difficult-to-characterize properties, and poorly understood biological functions. Electrochemical methods are revealing how melanin's redox-state molecular-switching is coupled to its electron-transfer activities. 
    more » « less
  • Citation Formats
  • MLA
  • APA
  • Chicago
  • BibTeX
  • Save / Share this Record
  • Send to Email