F. Pazos et al., Threading structural model of the manganese-stabilizing protein PsbO reveals presence of two possible beta-sandwich domains, PROTEINS, 45(4), 2001, pp. 372-381
The manganese-stabilizing protein (PsbO) is an essential component of photo
system II (PSII) and is present in all oxyphotosynthetic organisms. PsbO al
lows correct water splitting and oxygen evolution by stabilizing the reacti
ons driven by the manganese cluster. Despite its important role, its struct
ure and detailed functional mechanism are still unknown. In this article we
propose a structural model based on fold recognition and molecular modelin
g. This model has additional support from a study of the distribution of ch
aracteristics of the PsbO sequence family, such as the distribution of cons
erved, apolar, tree-determinants, and correlated positions. Our threading r
esults consistently showed PsbO as an all-beta (beta) protein, with two hom
ologous beta domains of approximately 120 amino acids linked by a flexible
Proline-Glycine-Glycine (PGG) motif. These features are compatible with a g
eneral elongated and flexible architecture, in which the two domains form a
sandwich-type structure with Greek key topology. The first domain is predi
cted to include 8 to 9 beta -strands, the second domain 6 to 7 beta -strand
s. An Ig-like beta -sandwich structure was selected as a template to build
the 3-D model. The second domain has, between the strands, long-loops rich
in Pro and Gly that are difficult to model. One of these long loops include
s a highly conserved region (between P148 and P174) and a short a-helix (be
tween E181 and N188)). These regions are characteristic parts of PsbO and s
how that the second domain is not so similar to the template. Overall, the
model was able to account for much of the experimental data reported by sev
eral authors, and it would allow the detection of key residues and regions
that are proposed in this article as essential for the structure and functi
on of PsbO. (C) 2001 Wiley-Liss, Inc.