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Figure 5. Model for the formation of a thioredoxin dimer bridged by a [2Fe-2S] iron–sulfur cluster. (A) Monomeric TrxA(CACA) is in equilibrium with a dimeric form of the protein (step 1). The catalytic sites constitute the dimer interface. The presence of four surface-exposed cysteine residues in the dimer interface allows the synthesis of an iron– sulfur cluster by the iron–sulfur cluster machinery (step 2). (B) Monomeric wild-type TrxA also forms weak dimers in vivo (step 1). However, only one cysteine residue is exposed in the catalytic site, which prevents the formation of an iron–sulfur cluster.
