Positive charges on lysine residues of the extrinsic 18 kDa protein are important to its electrostatic interaction with spinach photosystem II membranes.
To determine the contribution of charged amino acids to binding with the photosystem II complex (PSII), the amino or carboxyl groups of the extrinsic 18 kDa protein were modified with N-succinimidyl propionate (NSP) or glycine methyl ester (GME) in the presence of a water-soluble carbodiimide, respectively. Based on isoelectric point shift, 4-10 and 10-14 amino groups were modified in the presence of 2 and 4 mM NSP, respectively. Similarly, 3-4 carboxyl groups were modified by reaction with 100 mM GME. Neutralization of negatively charged carboxyl groups with GME did not alter the binding activity of the extrinsic 18 kDa protein. However, the NSP-modified 18 kDa protein, in which the positively charged amino groups had been modified to uncharged methyl esters, failed to bind with the PSII membrane in the presence of the extrinsic 23 kDa protein. This defect can not be attributed to structural or conformational alterations imposed by chemical modification, as the fluorescence and circular dichroism spectra among native, GME- and NSP-modified extrinsic 18 kDa proteins were similar. Thus, we have concluded that the positive charges of lysyl residues in the extrinsic 18 kDa protein are important for its interaction with PSII membranes in the presence of the extrinsic 23 kDa protein. Furthermore, it was found that the negative charges of carboxyl groups of this protein did not participate in binding with the extrinsic 23 kDa protein associated with PSII membranes.
Gao
Jin-Peng
JP
Institute of Plant Physiology and Ecology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200032, China.
Yong
Zhen-Hua
ZH
Zhang
Feng
F
Ruan
Kang-Cheng
KC
Xu
Chun-He
CH
Chen
Gen-Yun
GY
D001665:Binding Sites; D002462:Cell Membrane / Q000737:chemistry*; D005998:Glycine / Q000031:analogs & derivatives* / Q000737:chemistry; D008239:Lysine / Q000737:chemistry*; D008970:Molecular Weight; D045332:Photosystem II Protein Complex / Q000737:chemistry*; D011422:Propionates / Q000737:chemistry*; D011485:Protein Binding; D018724:Spinacia oleracea / Q000737:chemistry*; D055672:Static Electricity
D045332:Photosystem II Protein Complex; D011422:Propionates; C021749:N-succinimidyl propionate; C035591:glycine methyl ester; D008239:Lysine; D005998:Glycine