Vhr. Schmid et al., IN-VITRO RECONSTITUTION OF THE PHOTOSYSTEM-I LIGHT-HARVESTING COMPLEXLHCI-730 - HETERODIMERIZATION IS REQUIRED FOR ANTENNA PIGMENT ORGANIZATION, Proceedings of the National Academy of Sciences of the United Statesof America, 94(14), 1997, pp. 7667-7672
Here we describe the in vitro reconstitution of photosystem I light-ha
rvesting complexes with pigments and proteins (Lhca1 and Lhca4) obtain
ed by overexpression of tomato Lhca genes in Escherichia coil. Using L
hca1 and Lhca4 individually for reconstitution results in monomeric pi
gment-proteins, whereas a combination thereof yields a dimeric complex
. Interactions of the apoproteins is highly specific, as reconstitutio
n of either of the two constituent proteins in combination with a ligh
t-harvesting protein of photosystem II does not result in dimerization
. The reconstituted Lhca1/4, but not complexes obtained with either Lh
ca1 or Lhca4 alone, closely resembles the native LHCI-730 dimer from t
omato leaves with regard to spectroscopic properties, pigment composit
ion, and stoichiometry. Monomeric complexes of Lhcal or Lhca4 possess
lower pigment/protein ratios, indicating that interactions of the two
subunits not only facilitates pigment reorganization but also recruitm
ent of additional pigments. In addition to higher averages of chloroph
yll a/b ratios in monomeric complexes than in LHCI-730, comparative fl
uorescence and CD spectra demonstrate that heterodimerization involves
preferential ligation of more chlorophyll b.