jz5b02851_si_001.pdf (211.29 kB)
Mechanism of Water Delivery to the Active Site of Photosystem II along the S2 to S3 Transition
journal contribution
posted on 2016-01-26, 17:50 authored by Matteo Capone, Daniele Narzi, Daniele Bovi, Leonardo GuidoniThe two water molecules serving as
substrate for the oxygen evolution
in Photosystem II are already bound in the S2 state of
the Kok–Joliot’s cycle. Nevertheless, an additional
water molecule is supposed to bind the cluster during the transition
between the S2 and S3 states, which has been
recently revealed to have the Mn4CaO5 catalytic
cluster arranged in an open cubane fashion. In this Letter, by means
of ab initio calculations, we investigated the possible pathways for
the binding of the upcoming water molecule. Upon the four different
possibilities checked in our calculations, the binding of the crystallographic
water molecule, originally located nearby the Cl– binding site, showed the lowest activation energy barrier. Our findings
therefore support the view in which the W2 hydroxyl group and the
O5 oxygen act as substrates for the oxygen evolution. Within this
framework the role of the open and closed Mn4CaO5 conformers is clarified as well as the exact mechanistic events
occurring along the S2 to S3 transition.