The Trx-binding site lies at the interface between the FAD-and NADPH-binding domains. As described above, this binding site is crucial for electron transport and reduction of Trx. In FR conformation of the reductase, the active disulfide is presented on the surface, thus enabling the dithiol-disulfide interaction after binding of Trx. It was shown previously that an E. coli Trx-TrxR complex is formed by the interaction of the Trx-loop Tyr70-Ile75 (Ala67-Ile75 for Msm-TrxR) with a complementary cleft on the respective TrxR. Due to high sequence similarity, this can be transferred to Msm-TrxR. Another interaction occurs at E. coli's Phe141 and Phe142 (Phe143 and Phe144 for Msm-TrxR) with a hydrophobic pocket described by Lennon et al. and Koch et al. If fragments bind to these sites, the binding of Trx might be inhibited.