The SFB 1078 kindly invites you to the following colloquium talk:

Prof Hiroshi Ishikita

Research Center for Advanced Science and Technology, The University of Tokyo, Japan

Title: 

Light-induced electron transfer and proton transfer in photosystem II

Abstract: 

Type-II photosynthetic reaction centers, such as purple bacterial reaction centers (PbRC) and the oxygen-evolving enzyme photosystem II (PSII) utilize electron-transfer pathways for their light-driven energy conversion. In PSII, the catalytic Mn4CaO5/6 cluster facilitates oxygen evolution by releasing electrons and protons from two substrate water molecules.

Electron removal from substrate water molecules proceeds via a pathway from Mn4CaO5/6 to the redox-active tyrosine (TyrZ) and photo-oxidized chlorophyll, driven by the redox-potential cascade. In contrast, proton release requires the formation of low-barrier hydrogen bonds, a concept elucidated by Arieh Warshel (Nobel Prize in Chemistry, 2013). These low-barrier hydrogen bonds are characterized by symmetric potential-energy curves, indicating nearly equal pKa values for the hydrogen bond moieties.

This talk will explore the involvement of low-barrier hydrogen bonds in proton transfer in Type-II reaction centers, including processes such as proton release from substrate water molecules and proton-coupled electron transfer between quinone cofactors.