Evidence for a subgroup of thioredoxin h that requires GSH/Grx for its reduction.

Poplar thioredoxin h4 (popTrxh4) and a related CXXS type (popCXXS3) are both members of a plant thioredoxin h subgroup. PopTrxh4 exhibits the usual catalytic site WCGPC, whereas popCXXS3 harbors the non-typical active site WCMPS. Recombinant popTrxh4 and popCXXS3 are not reduced either by Arabidopsis thaliana NADPH-dependent thioredoxin reductases (NTR) A and B or by Escherichia coli NTR. We report here evidence that a poplar glutaredoxin as well as three E. coli Grxs are able to reduce popTrxh4. PopTrxh4 is able to reduce several thioredoxin targets as peroxiredoxins or methionine sulfoxide reductases. On the other hand, popCXXS3 exhibits an activity in the presence of glutathione and hydroxyethyldisulfide. Except for examples of glutathiolation, these are the first two examples of a direct interconnection between the thioredoxin and glutathione/glutaredoxin systems.