PDIA3/ERp57, a multifunctional protein
P41009
G. PagliaI, M. EufemiI, L. CervoniI, S. ChichiarelliI, F. GiamoganteI, S. CarissimiI, E. RubiniI, F. AltieriI
IDepartment of Biochemical Sciences "A. Rossi Fanelli" Sapienza University of Rome, Rome, Italy
PDIA3 is a member of the protein disulfide isomerase family mainly found in the endoplasmic reticulum where it modulates the folding of newly synthesized glycoproteins. PDIA3 is also involved in several human diseases due to its multisubcellular localization, its overexpression in cancer and above all flexible binding sites. Taking into account the ability of PDIA3 to interact with a series of small ligands, e.g. flavonoids, the thermodynamic parameters, binding constants and the effects on enzymatic activity of the interaction between PDIA3 and a wide range of flavonoids were characterized. Two flavonoids, silibinin and punicalagin, showed the ability to bind and modify protein properties in the micromolar range of concentration. In order to understand if the silibinin and punicalagin binding effects are only PDIA3 specific, the aim of this study is to perform a comparative study between PDIA1 and PDIA3. Flavonoids’ binding and the effects on both proteins were evaluated by quenching analysis of the protein intrinsic fluorescence, differential scanning calorimetry and isothermal titration calorimetry assays, while disulfide reductase activity was assayed with a fluorescent substrate. The punicalagin and silibinin exhibit different behaviours on both PDIAs suggesting that the interactions between flavonoids and PDIAs involve different binding sites. The ability of the silibinin and punicalagin to modulate PDIAs could be used in the treatment of diseases in which the PDIAs are overexpressed, such as in different types of cancer, in platelet aggregation where PDIA3 plays an important role and as adjuvant in chemotherapy promoting endoplasmic reticulum stress and apoptosis.