ArticleJournal of the American Chemical Society2011
Slow dissociation of a charged ligand: analysis of the primary quinone Q(A) site of photosynthetic bacterial reaction centers.
Article in Journal of the American Chemical Society, 2011. The graph could read no effect estimate from its abstract, so it casts no vote on the map. Cited by 6 papers.
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Who cites it
6 citing papers in PubMed, 16 citations in OpenAlex.
- Molecular dynamics simulations in photosynthesis.Photosynthesis research · 2020Review
- Redox-coupled quinone dynamics in the respiratory complex I.Proceedings of the National Academy of Sciences of the United States of America · 2018Article
- Affinity and activity of non-native quinones at the Q(B) site of bacterial photosynthetic reaction centers.Photosynthesis research · 2014Article
- A review on the role of quinones in renal disorders.SpringerPlus · 2013Article
- Article
- Molecular mechanisms for generating transmembrane proton gradients.Biochimica et biophysica actaReview
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Authors and funding
4 authors at 1 institution in 1 country.
Funding
Abstract
Reaction centers (RCs) are integral membrane proteins that undergo a series of electron transfer reactions during the process of photosynthesis. In the Q(A) site of RCs from Rhodobacter sphaeroides, ubiquinone-10 is reduced, by a single electron transfer, to its semiquinone. The neutral quinone and anionic semiquinone have similar affinities, which is required for correct in situ reaction thermodynamics. A previous study showed that despite similar affinities, anionic quinones associate and dissociate from the Q(A) site at rates ≈10(4) times slower than neutral quinones indicating that anionic quinones encounter larger binding barriers (Madeo, J.; Gunner, M. R. Modeling binding kinetics at the Q(A) site in bacterial reaction centers. Biochemistry 2005, 44, 10994-11004). The present study investigates these barriers computationally, using steered molecular dynamics (SMD) to model the unbinding of neutral ground state ubiquinone (UQ) and its reduced anionic semiquinone (SQ(-)) from the Q(A) site. In agreement with experiment, the SMD unbinding barrier for SQ(-) is larger than for UQ. Multi Conformational Continuum Electrostatics (MCCE), used here to calculate the binding energy, shows that SQ(-) and UQ have comparable affinities. In the Q(A) site, there are stronger binding interactions for SQ(-) compared to UQ, especially electrostatic attraction to a bound non-heme Fe(2+). These interactions compensate for the higher SQ(-) desolvation penalty, allowing both redox states to have similar affinities. These additional interactions also increase the dissociation barrier for SQ(-) relative to UQ. Thus, the slower SQ(-) dissociation rate is a direct physical consequence of the additional binding interactions required to achieve a Q(A) site affinity similar to that of UQ. By a similar mechanism, the slower association rate is caused by stronger interactions between SQ(-) and the polar solvent. Thus, stronger interactions for both the unbound and bound states of charged and highly polar ligands can slow their binding kinetics without a conformational gate. Implications of this for other systems are discussed.
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