Structure
E. coli thioredoxin reductase structure: In E. coli ThxR there is are two binding domains, one for FAD and another for NADPH. The connection between these two domains is a two-stranded anti-parallel f3-sheet. Each domain individually is very similar to the analogous domains in glutathione reductase, and lipoamide dehydrogenase but they relative orientation of these domains in ThxR is rotated by 66 degrees. This becomes significant in the enzyme mechanism of action which is described below. ThxR homo-dimerizes with the interface between the two monomers formed by three alpha-helicies and two loops. Each monomer can separately bind a molecule of thioredoxin.
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Structure of E. coli ThxR dimer bound thioredoxin
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Structure of E. coli ThxR with FAD and NADPH prosthetic groups labeled
Mammalian thioredoxin reductase structure: Mammalian TrxR structure is similar to E. coli. It contains a FAD and NADPH binding domain, and an interface between two monomer subunits. In mammalian ThxR there is an insertion in the FAD binding domain between two alpha helices which forms a small pair of beta strands. The active disulfide in the enzyme is located on one of these helices and thus the active disulfide bond is located in the FAD domain and not the NADPH domain as in E. coli and other prokaryotes.
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Structure of human ThxR FAD and NADPH prosthetic groups
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“There is no such thing as a language, not if a language is anything like what many philosophers and linguists have supposed. There is therefore no such thing to be learned, mastered, or born with. We must give up the idea of a clearly defined shared structure which language-users acquire and then apply to cases.”
—Donald Davidson (b. 1917)