Crystal structures of the photosystem II D1 C-terminal processing protease

We report here the first three-dimensional structure of the D1 C-terminal p rocessing protease (DIP), which is encoded by the ctpA gene. This enzyme re moves the C-terminal extension of the D1 polypeptide of photosystem II of o xygenic photosynthesis, Proteolytic processing is necessary to allow the li ght driven assembly of the tetranuclear manganese duster, which is responsi ble for photosynthetic water oxidation. The X-ray structure of the Scenedes mus obliquus enzyme has been determined at 1.8 Angstrom resolution using th e multiwavelength anomalous dispersion method. The enzyme is monomeric and is composed of three folding domains. The middle domain is topologically ho mologous to known PDZ motifs and is proposed to be the site at which the su bstrate C-terminus binds. The remainder of the substrate likely extends acr oss the face of the enzyme, interacting at its scissile bond with the enzym e active site Ser 372/Lys 397 catalytic dyed, which lies at the center of t he protein at the interface of the three domains.