NMR solution structure of plastocyanin from the photosynthetic prokaryote,Prochlorothrix hollandica

The solution structure of a divergent plastocyanin (PC) from the photosynth etic prokaryote Prochlorothrix hollandica was determined by homonuclear H-1 NMR spectroscopy. Nineteen structures were calculated from 1222 distance r estraints, yielding a family of structures having an average rmsd of 0.42 /- 0.08 Angstrom, for backbone atoms and 0.71 +/- 0.07 Angstrom for heavy a toms to the mean structure. No distance constraint was violated by more tha n 0.26 Angstrom in the structure family. Despite the low number of conserve d residues shared with other PC homologues, the overall folding pattern of P. hollandica PC is similar to other PCs, in that the protein forms a two-s heet beta-barrel tertiary structure. The greatest variability among the bac kbone structures is seen in the loop region from residues 47-60. The differ ences seen in the P. hollandica PC homologue likely arise due to a small de letion of 2-4 residues compared to the PC consensus; this yields a less ext ended loop containing a short alpha-helix from residues Ala52-Leu55. Additi onally, the protein has an altered hydrophobic patch thought to be importan t in binding reaction partners. Whereas the backbone structure is very simi lar within the loops of the hydrophobic region, the presence of two unique residues (Tyr12 and Pro14) yields a structurally different hydrophobic surf ace likely important in binding P. hollandica Photosystem I.