The crystal structure of two of these members shows that this domain has a ferredoxin like fold and is likely to exists as at least homodimers. Sulphate ions are are located at the dimer interfaces, which are thought to confer additional stability. Although the function of this domain remains to be identified, its structure suggests a role in protein-protein interactions possibly regulated by the binding of small-molecule ligands [1]. Solution of the structure of the hyperthermophilic anaerobic Thermotoga maritima sequence, UniProtKB:Q9WYV6, shows that this has a beta-alpha-beta-beta-alpha-beta ferredoxin-like fold and assembles as a homotetramer. It was possible to identify a pocket in each monmer that bound an unidentified ligand. It was also found that it bound charged thiamine though not hydroxymethyl pyrimidine. It is proposed that it is transporting charged thiamine around the cytoplasm. Under oxidative conditions this bacterium is under stress, and the transcriiptional unit within which this protein is expressed is up-regulated in these conditions, suggesting that the chelation of cytoplasmic thaimine is part of the response mechanism to such oxidatvie stress, which is mediated by this family [2].

1: Crystal structures of MTH1187 and its yeast ortholog YBL001c. Tao X, Khayat R, Christendat D, Savchenko A, Xu X, Goldsmith-Fischman S, Honig B, Edwards A, Arrowsmith CH, Tong L; Proteins 2003;52:478-480. PMID:12866058

2: TM0486 from the hyperthermophilic anaerobe Thermotoga maritima is a thiamin-binding protein involved in response of the cell to oxidative conditions. Dermoun Z, Foulon A, Miller MD, Harrington DJ, Deacon AM, Sebban-Kreuzer C, Roche P, Lafitte D, Bornet O, Wilson IA, Dolla A; J Mol Biol. 2010;400:463-476. PMID:20471400