The binding of silibinin to ERp57

•Silibinin interacts with ERp57 by submicromolar dissociation constant.•We found that silibinin enhances the formation of ERp57/REF-1 complex.•Silibinin appears to affect the intracellular distribution of ERp57.

The flavonoid silibinin is known to intervene in many cellular processes involved in a variety of pathologies, thus appearing a promising therapeutic tool. The molecular mechanisms responsible for these activities, however, have not been clearly defined, and although some of its interactions with proteins have been identified, the relative affinities are often too low to appear relevant in vivo. Here we describe the interaction of silibinin with the protein disulfide isomerase ERp57, characterized by a submicromolar dissociation constant. This interaction enhances the formation of a ERp57/REF-1 complex, and furthermore appears to affect the intracellular distribution of ERp57. This protein is involved in signaling pathways which are also affected by silibinin. This suggests that the ERp57–silibinin interaction might explain at least some of the biological effects caused by the flavonoid.