Structure of plastocyanin from the cyanobacterium Anabaena variabilis

Plastocyanin from the cyanobacterium Anabaena variabilis was heterologously produced in Escherichia coli and purified. Plate-like crystals were obtained by crystallization in 1.15 M trisodium citrate and 7.67 mM sodium borate buffer pH 8.5. The crystals belong to the orthorhombic space group P2₁2₁2₁, with unit-cell parameters a = 67.85, b = 45.81, c = 63.41 Å. The structure of the oxidized protein was solved to a resolution of 1.6 Å using plastocyanin from Phormidium laminosum as a search model. Two molecules were found in the asymmetric unit. The electrostatic surface of the basic protein showed a large population of positively charged residues in the northern site, whereas the eastern site lacked the two strongly negatively charged patches. The copper ion was found to be relatively mobile and there were two distinct conformations of His61.