NMR SOLUTION STRUCTURE OF AN OXIDIZED THIOREDOXIN-H FROM THE EUKARYOTIC GREEN-ALGA CHLAMYDOMONAS-REINHARDTII

NMR solution structures of a cytosolic plant thioredoxin h (112 amino acids, 11.7 kDa) from the green alga Chlamydomonas reinhardtii have be en calculated on the basis of 1904 NMR distance restraints, which incl ude 90 distances used to restrain 45 hydrogen bonds, and 44 phi dihedr al restraints. The structure of C. reinhardtii thioredoxin h was solve d in its oxidised form, and the ensemble of 23 converged structures su perpose to the geometric average structure with an atomic rmsd of 0.08 0 nm+/-0.016 for the (N, C alpha C) backbone atoms of residues 4-110. Comparisons with other thioredoxins, such as thioredoxin from the bact erium Escherichia coli, thioredoxin 2 from a cyanobacterium of the Ana baena genus, and human thioredoxin, showed that thioredoxin h models s hare more structural features with human thioredoxin than with other b acterial thioredoxins. Examination of the accessible surface around th e redox-active peptide sequence indicates that a potent thioredoxin-h- substrate interaction could be similar to the vertebrate thioredoxin-s ubstrate interactions.