CRYSTAL-STRUCTURE OF SPINACH PLASTOCYANIN AT 1.7 ANGSTROM RESOLUTION

The crystal structure of plastocyanin from spinach has been determined using molecular replacement, with the structure of plastocyanin from poplar as a search model. Successful crystallization was facilitated b y site-directed mutagenesis in which residue Gly8 was substituted with Asp. The region around residue 8 was believed to be too mobile for th e wild-type protein to form crystals despite extensive screening. The current structure represents the oxidized plastocyanin, copper in), at low pH (approximate to 4.4). In contrast to the similarity in the cor e region as compared to its poplar counterpart, the structure shows so me significant differences in loop regions. The most notable is the la rge shift of the 59-61 loop where the largest shift is 3.0 Angstrom fo r the C-alpha atom of Glu59. This results in different patterns of ele ctrostatic potential around the acidic patches for the two proteins.