The NADPH Thioredoxin Reductase C from Cyanobacterium Thermosynechococcus elongatus BP-1 Has a Chaperone Activity Regulated by a 2-Cys Peroxiredoxin and NADPH.

Abstract

Peroxiredoxins are ubiquitous thiol peroxidases which catalyze the reduction of hydroperoxide. Among them, 2-Cys peroxiredoxin has been proposed to play a key role in the regulation of H₂O₂ level. We have described that an NADPH thioredoxin reductase C (NTRC) is a reductant for a 2-Cys peroxiredoxin which is called BAS1 in a thermophilic cyanobacterium Thermosynechococcus elongatesBP-1. In this work, we discovered that NTRC has a chaperone activity in addition to the peroxiredoxin reductase activity. Although the thermal aggregation of citrate synthase was not reduced by the addition of BAS1, it was efficiently prevented by the addition of NTRC in dose dependent manner, indicating that NTRC protects citrate synthase against thermal aggregation. In the absence of NADPH, NTRC and BAS1 formed aggregates which showed no chaperone activity. The aggregates were dissociated by the addition of NADPH, resulting in recovery of the chaperone activity of NTRC. The molecular mechanisms of the reversible formation of the aggregates of NTRC and BAS1 will be discussed.