Crystal structures of wild-type and mutant plastocyanins from a higher plant, Silene

Plastocyanin functions as an electron carrier between the cytochrome b(6)f complex and photosystem I, The crystal structures of the wild-type and E43K/D44K double mutant from the higher plant, Silene, have been determined at 2.0 and 1.75 Angstrom resolution, respectively, The wild-type plastocyanin comprises two monomers per asymmetric unit, one of which shows the unusually great distance between the copper ion and the N-delta 1 atom of H87 because of the hydrogen bond network formation between H87 and symmetry-related G10, The root mean square deviation for Ca atoms between the wild-type and mutant plastocyanins is 0.44 Angstrom, however, the electrostatic potential maps of their molecular surfaces are remarkably different. The low electron-transfer rate in the E43K/D44K mutant results from the hindrance of electrostatic interactions, not from the structural change due to the mutation.