HOMOLOGY PREDICTED STRUCTURE AND COMPARISON WITH THE SECONDARY STRUCTURE FROM NMR DATA FOR PLASTOCYANIN FROM THE CYANOBACTERIUM SYNECHOCYSTIS SP PCC-6803

Sequence specific H-1 NMR resonance assignments are reported here for 95 amino acids of reduced plastocyanin from the cyanobacterium Synecho cystis sp. PCC 6803 at pH 5.4. Spin systems of different amino acids w ere classified and identified using DQF-COSY and TOCSY spectra in D2O and H2O solvents. A variety of temperature conditions and two magnetic fields (400 and 600 MHz) were used to overcome resonance overlap. Seq uence specific assignment of the spin systems was made using NOE conne ctivities between adjacent amide, alpha and beta protons (alpha(i)-Nii +1, N-i-Nii+1 and beta(i)-Ni+1). A selection of beta H stereospecific assignments and chi(1) angles for some buried and surface residues of Synechocystis plastocyanin are presented as well. Analysis of interres idue NOE connectivities made possible the characterization of the seco ndary structure, which is of the beta-sheet type as is the case in all other plastocyanins. The protein in solution contains eight beta-stra nds, one short alpha-helix segment, five reverse turns and two loops. However, some differences in local conformation are observed between c yanobacterial, algal and higher plant plastocyanins. Four different ho mologous proteins as templates, two distinct alignments and two approa ches (MODELLER and CONGEN) were used to model the three-dimensional st ructure of Synechocystis plastocyanin. The lowest energy predicted str uctures reported herein can be considered of medium range resolution ( similar to 3 Angstrom). The detailed analysis of hydrogen bonded amide protons in Synechocystis models, the slowly exchanging amide protons determined by NMR, and comparison with hydrogen bonds in other charact erized plastocyanins indicate that the folding of Synechocystis plasto cyanin is quite similar to that of other plastocyanins. (C) 1998 Elsev ier Science S.A. All rights reserved.