Calculated coupling of electron and proton transfer in the photosynthetic reaction center of Rhodopseudomonas viridis.
AUTOR(ES)
Lancaster, C R
RESUMO
Based on new Rhodopseudomonas (Rp.) viridis reaction center (RC) coordinates with a reliable structure of the secondary acceptor quinone (QB) site, a continuum dielectric model and finite difference technique have been used to identify clusters of electrostatically interacting ionizable residues. Twenty-three residues within a distance of 25 A from QB (QB cluster) have been shown to be strongly electrostatically coupled to QB, either directly or indirectly. An analogous cluster of 24 residues is found to interact with QA (QA cluster). Both clusters extend to the cytoplasmic surface in at least two directions. However, the QB cluster differs from the QA cluster in that it has a surplus of acidic residues, more strong electrostatic interactions, is less solvated, and experiences a strong positive electrostatic field arising from the polypeptide backbone. Consequently, upon reduction of QA or QB, it is the QB cluster, and not the QA cluster, which is responsible for substoichiometric proton uptake at neutral pH. The bulk of the changes in the QB cluster are calculated to be due to the protonation of a tightly coupled cluster of the three Glu residues (L212, H177, and M234) within the QB cluster. If the lifetime of the doubly reduced state QB2- is long enough, Asp M43 and Ser L223 are predicted to also become protonated. The calculated complex titration behavior of the strongly interacting residues of the QB cluster and the resulting electrostatic response to electron transfer may be a common feature in proton-transferring membrane protein complexes.
ACESSO AO ARTIGO
http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1225230Documentos Relacionados
- Microaerophilic growth and induction of the photosynthetic reaction center in Rhodopseudomonas viridis.
- A system for site-specific mutagenesis of the photosynthetic reaction center in Rhodopseudomonas viridis.
- Nobel lecture. The photosynthetic reaction centre from the purple bacterium Rhodopseudomonas viridis.
- Gene transfer system for Rhodopseudomonas viridis.
- Nitrogen fixation and ammonia switch-off in the photosynthetic bacterium Rhodopseudomonas viridis.