Identification of domains on the extrinsic 33-kDa protein possibly involved in electrostatic interaction with photosystem II complex by means of chemical modification

The extrinsic 33-kDa protein of photosystem II (PSII) was modified with various reagents, and the resulting proteins were checked for the ability to rebind to PSII and to reactivate oxygen evolution. While modification of more than eight carboxyl groups of aspartyl and glutamyl residues with glycine methyl ester did not affect the rebinding and reactivating capabilities, modification of amino groups of lysyl residues with either N-succinimidyl propionate or 2,4,6-trinitrobenzene sulfonic acid or modification of guanidino groups of arginyl residues with 2,3-butanedione resulted in a loss of rebinding and reactivating capabilities of the 33-kDa protein. Moreover, the number of lysyl and arginyl residues susceptible to modification was significantly decreased when the protein was bound to PSII as compared with when it was free in solution, whereas the number of carboxyl groups modified was little affected. These results suggested that positive charges are important for the electrostatic interaction between the extrinsic 33-kDa protein and PSII intrinsic proteins, whereas negative charges on the protein do not contribute to such interaction. By a combination of protease digestion and mass spectroscopic analysis, the domains of lysyl residues accessible to N-succinimidyl propionate or 2,4,6-trinitrobenzene sulfonic acid modification only when the 33-kDa protein is free in solution were determined to be Lys ⁴, Lys ²⁰, Lys ⁶⁶-Lys ⁷⁶, Lys ¹⁰¹, Lys ¹⁰⁵, Lys ¹³⁰, Lys ¹⁵⁹, Lys ¹⁸⁶, and Lys ²³⁰-Lys ²³⁶. These domains include those previously reported accessible to N-hydroxysuccinimidoblotin only in solution (Frankel and Bricker (1995) Biochemistry 34, 7492-7497), and may be important for the interaction of the 33-kDa protein with PSII intrinsic proteins.