Close association of the 33 kDa extrinsic protein with the apoprotein of CPa1 in photosystem II
Abstract
The structural arrangement of the extrinsic 33 kDa protein and the 49/53 kDa apoprotein of CPa1 were investigated in oxygen-evolving photosystem II preparations. N-Hydrosuccinimidobiotin (NHS-biotin) was used to label accessible amino groups in control, NaCl-, CaCl2- and alkaline tris-washed membranes. Labeling of the apoprotein of CPa1 was observed in treatments which removed the extrinsic 33 kDa protein. The water-soluble carbodiimide, 1-ethyl-3(3-dimethylaminopropyl)carbodiimide (EDC) was used to crosslink proteins with complementary charged groups in close proximity to one another. Two crosslinked complexes of the extrinsic 33 kDa and the CPa1 apoprotein were observed at 76 and 65 kDa. These complexes were not formed in membranes lacking the 33 kDa extrinsic protein. Finally, the homobifunctional cleavable crosslinker, dithiobis[succinimidylpropionate] (DTSP), was used to reversibly crosslink the 33 kDa extrinsic protein with the apoprotein of CPa1 in oxygen-evolving PS II core complex preparations. These results suggest a very close association of the extrinsic 33 kDa protein and the apoprotein of CPa1 in the photosynthetic membrane. We suggest that the apoprotein of CPa1 may provide a binding site for the 33 kDa extrinsic component. © 1988.