Amino acid sequence determination and three-dimensional modelling of thioredoxin from the photosynthetic bacterium Rhodobacter sphaeroides Y.

The complete primary structure of thioredoxin from Rhodobacter sphaeroides Y has been determined by analysis of peptides after cleavage with cyanogen bromide, chymotrypsin and trypsin. Peptides were separated by HPLC and analyzed by liquid-phase and gas-phase sequencer degradations. The protein consists of 105 residues (Mr = 11,180); its amino acid sequence shows a clear homology to the five known thioredoxins from plant or bacterial sources, with 40-56% residue identity when the proteins are aligned at the active-site disulfide. Not only the active-site regions are conserved, but also residues which belong to the hydrophobic surface suggested to be important for binding of procaryote thioredoxins in redox interactions with other proteins (residues 75-76; 91-93 in Escherichia coli). A three-dimensional model of Rb. sphaeroides thioredoxin has been derived from the E. coli crystallographic structure with computer graphics. This model indicates that the overall structures as well as the active sites are closely similar; however, the residue substitutions allow both proteins to adopt different local folding as shown in the hydrophobic core.