Thioredoxins are enzymes found in all cells. They participate in a broad range of biological processes, including cell proliferation, blood clotting, seed germination, insulin degradation, repair of oxidative damage, and enzyme regulation. The common mechanism of these activities is the reduction of protein disulphide bonds.

Plate VII shows a multiple sequence alignment of 16 thioredoxins. The structure of E. coli thioredoxin contains a central five-stranded ?-sheet flanked on either side by ?-helices; these helices and strands are indicated by the symbols ? and ?. Other thioredoxins are expected to share most but not all of the secondary structure of the E. coli enzyme. The plate also shows a summary of the alignment as a sequence logo, in which letters of different sizes indicate different proportions of amino acids. (T. Schneider and M. Stephens designed sequence logos; this example was produced using the webserver of S.E. Brenner, http://www.bio.cam.ac.uk/cgi-bin/seqlogo/logo.cgi).

Plate VII: (a) Alignment of amino-acid sequences of E. coli thioredoxin and homologues. Some of the sequences have been trimmed at their termini. Residue numbers in this table correspond to positions in the E. coli sequence (top line). Helix (a) and strand ( ?) assignments for E. coli thioredoxin are from PDB entry 2TRX. (b) Sequence logo derived from this multiple-sequence alignment. (c) The structure of E. coli thioredoxin [2TRX] contains a central five-stranded ?-sheet flanked on either side by ?-helices. Residue...