Dynamics in Photo system II Structure and Function
11
@
N
@®
DI
G @@\ @@ 0
0 . 1 8~!m Io<~IV 1-[oJ T ® ~ 'elixV
Io
® i' " ~ iJ'
. ". 134® Y w .. ". y
i.nH
f;\
~'" Q~'" "~.~ .. ' 'QB ~
G
V
s~ ~N ....... ,U0211 88 ~I
y
® A
ni-H 15
@
®
;:. ®
R ""Dl
~2
~n
The transmembrane helices viewed
from the donor side
D2
\!J
®..
E
beli.m
',bV
® ®
~....fi')
®0
®w
Italics: mutations in herbicide tolerance
Fig. 1.4. A blow up view of the extended loop in the reaction center polypeptides of Dl
and D2 photosystem II in the membrane. Viewed from the matrix (acceptor) side. A
possible folding of the extended loops that are in contact above the quinone-binding sites
is indicated out of scale. Ten transmembrane helices of the two polypeptides are indicated
as circles. As these helices are tilted in the membrane, their order is somewhat different
when viewed either from the matrix or lumen side. (Italics: mutations in herbicide
tolerance)
D1 protein. As will be discussed below, it is in this extended loop that
dynamic properties of possibly regulatory significance in photosynthesis take
place. The extended loop in the D1 and also the D2 protein will fold
differently from the shorter sequence in the homologous Land M subunits.
It has been proposed (Trebst 1991) that they fold back above the OA and
Os sites and provide a contact point where the structural and functional
information between the two quinone-binding sites can be exchanged
(Fig. 1.4).
It appears that the correlation of structure and function of photosystem II
is well based and makes it possible to address many detailed questions
on the molecular mechanism in a photosystem at a highly sophisticated
biophysical level (Lauterwasser et al. 1992). This chapter will not address
this, but instead focus on an aspect of regulation of photosystem II activity.
1.4 Dynamics in the Dl Protein in Rapid Turnover
and Stress-Enhanced Photoinhibition
Photo system II has a suprising property. Although designed to absorb light
and split water to oxygen, it is also light-sensitive, and this particularly in the
presence of oxygen. Photosystem II function is easily inactivated by excess
11
@
N
@®
DI
G @@\ @@ 0
0 . 1 8~!m Io<~IV 1-[oJ T ® ~ 'elixV
Io
® i' " ~ iJ'
. ". 134® Y w .. ". y
i.nH
f;\
~'" Q~'" "~.~ .. ' 'QB ~
G
V
s~ ~N ....... ,U0211 88 ~I
y
® A
ni-H 15
@
®
;:. ®
R ""Dl
~2
~n
The transmembrane helices viewed
from the donor side
D2
\!J
®..
E
beli.m
',bV
® ®
~....fi')
®0
®w
Italics: mutations in herbicide tolerance
Fig. 1.4. A blow up view of the extended loop in the reaction center polypeptides of Dl
and D2 photosystem II in the membrane. Viewed from the matrix (acceptor) side. A
possible folding of the extended loops that are in contact above the quinone-binding sites
is indicated out of scale. Ten transmembrane helices of the two polypeptides are indicated
as circles. As these helices are tilted in the membrane, their order is somewhat different
when viewed either from the matrix or lumen side. (Italics: mutations in herbicide
tolerance)
D1 protein. As will be discussed below, it is in this extended loop that
dynamic properties of possibly regulatory significance in photosynthesis take
place. The extended loop in the D1 and also the D2 protein will fold
differently from the shorter sequence in the homologous Land M subunits.
It has been proposed (Trebst 1991) that they fold back above the OA and
Os sites and provide a contact point where the structural and functional
information between the two quinone-binding sites can be exchanged
(Fig. 1.4).
It appears that the correlation of structure and function of photosystem II
is well based and makes it possible to address many detailed questions
on the molecular mechanism in a photosystem at a highly sophisticated
biophysical level (Lauterwasser et al. 1992). This chapter will not address
this, but instead focus on an aspect of regulation of photosystem II activity.
1.4 Dynamics in the Dl Protein in Rapid Turnover
and Stress-Enhanced Photoinhibition
Photo system II has a suprising property. Although designed to absorb light
and split water to oxygen, it is also light-sensitive, and this particularly in the
presence of oxygen. Photosystem II function is easily inactivated by excess