Lk. Frankel et al., Carboxylate groups on the manganese-stabilizing protein are required for its efficient binding to photosystem II, BIOCHEM, 38(43), 1999, pp. 14271-14278
The effects of the modification of carboxylate groups on the manganese-stab
ilizing protein of photosystem II were investigated. Carboxylate groups (in
cluding possibly the C-terminus) on the manganese-stabilizing protein were
modified with glycine methyl ester in a reaction facilitated by 1-ethyl-3-
[3-(dimethylamino)propyl]carbodiimide. The manganese-stabilizing protein th
at was modified while associated with NaCl-washed photosystem II membranes
contained 1-2 modified carboxylates, whereas the protein that was modified
while free in solution contained 4 modified carboxylates. Both types of mod
ified protein could reconstitute oxygen evolution at high manganese-stabili
zing protein to photosystem II reaction center ratios. However, the protein
that had been modified in solution exhibited a dramatically altered bindin
g affinity for photosystem LT. No such alteration in binding affinity was o
bserved for the protein that had been modified while associated with the ph
otosystem. Mapping of the sites of modification was carried out by trypsin
and Staphylococcus V8 protease digestion of the modified proteins and analy
sis by matrix-assisted laser desorption/ionization mass spectrometry. These
studies indicated that the domains D-157-D-168 and E-212-(247)Q (C-terminu
s) are labeled only when the manganese-stabilizing protein is modified in s
olution. Modified carboxylates in these domains are responsible for the alt
ered binding affinity of this protein for the photosystem.