Mechanism of the formation of proton transfer pathways in photosynthetic reaction centers
Yu Sugo, Keisuke Saito, Hiroshi Ishikita
Abstract
Significance The crystal structures of photosynthetic reaction centers from purple bacteria (PbRCs) and photosystem II show large structural similarity. However, the proposed mechanisms of proton transfer toward the terminal electron acceptor quinone (Q B ) are not consistent. In particular, not His-L190, which is an H-bond partner of Q B , but rather Glu-L212, which is ∼6 Å away from Q B , was assumed to be the direct proton donor for Q B . We demonstrate that the H-bond between His-L190 and Q B is a low-barrier H-bond, which facilitates proton transfer from singly protonated His-L190 to Q B . Furthermore, Glu-L212 is not a direct H-bond donor for Q B . However, it facilitates proton transfer toward deprotonated His-L190 via water molecules after Q B H 2 forms and leaves the PbRC.