Expression in Escherichia coli of the extrinsic 18-kDa protein of photosystem II of spinach.

A cDNA encoding the precursor for the 18-kDa protein of PSII of spinach was expressed in Escherichia coli. When the cell lysate was incubated at 7 degrees C, the precursor was degraded by proteases of E. coli to a polypeptide of 18 kDa (P18) that consisted of the mature protein moiety plus the last four residues of the transit peptide. P18 was able to reconstitute the water-oxidizing complex of NaCl-treated PSII membranes supplemented with the 23-kDa protein. Moreover, P18 was cleaved by the prolyl endoproteinase of spinach specifically at the Pro-12-Leu-13 bond, as was the authentic 18-kDa protein. These properties of P18 indicate that the present expression system is potentially useful for studies of the substrate specificity of the endoproteinase, as well as of the structure-function relationships of the 18-kDa protein.