Background: Protein-disulfide isomerase (PDI) has previously been identified to bind bisphenol A (BPA), an endocrine disrupter.Results: BPA inhibited Ero1α-PDI-mediated disulfide bond formation.Conclusion: BPA significantly inhibited the Ero1α and PDI oxidative cycle, probably through closure of the substrate- and Ero1α-binding pocket in the PDI b′ domain.Significance: BPA may have inhibitory effects on oxidative folding of secretory and membrane proteins.

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In erythrocytes, 4.1R80 (80 kDa isoform of protein 4.1R) binds to the cytoplasmic tail of the transmembrane proteins band 3 and GPC (glycophorin C), and to the membrane-associated protein p55 through the N- (N-terminal), α- (α-helix-rich) and C- (C-terminal) lobes of R30 [N-terminal 30 kDa FERM (4.1/ezrin/radixin/moesin) domain of protein 4.1R] respectively. We have shown previously that R30 binds to CaM (calmodulin) in a Ca2+-independent manner, the equilibrium dissociation constant (Kd) for R30-CaM binding being very similar (in the submicromolar range) in the presence or absence of Ca2+. In the present study, we investigated the consequences of CaM binding on R30's structural stability using resonant mirror detection and FTIR (Fourier-transform IR) spectroscopy. After a 30 min incubation above 40° C, R30 could no longer bind to band 3 or to GPC. In contrast, R30 binding to p55, which could be detected at a temperature as low as 34° C, was maintained up to 44° C in the presence of apo-CaM. Dynamic light scattering measurements indicated that R30, either alone or complexed with apo-CaM, did not aggregate up to 40° C. FTIR spectroscopy revealed that the dramatic variations in the structure of the β-sheet structure of R30 observed at various temperatures were minimized in the presence of apo-CaM. On the basis of Kd values calculated at various temperatures, ΔCp and ΔG° for R30 binding to apo-CaM were determined as -10 kJ · K(-1) · mol-1 and ~ -38 kJ · mol(-1) at 37° C (310.15 K) respectively. These data support the notion that apo-CaM stabilizes R30 through interaction with its β-strand-rich C-lobe and provide a novel function for CaM, i.e. structural stabilization of 4.1R80.

a b s t r a c tAmyloid fibrils are fibrous protein assemblies with distinctive cross-b structures. For amyloidosis, there are disease-associated mutations outside of the cross-b structures. Thus, it is necessary to elucidate the role of peripheral sequences outside the cross-b structure. Amyloid fibrils are generally 10 nm in width; however, the amyloid fibrils of truncated barnase M1 peptides missing the Cterminal sequence outside the cross-b structure are 20 nm in width. In this study, we performed comparative analysis of the structural stability of amyloids formed by the respective peptides. We found that the C-terminal amino acids dramatically affect the conformational instability in the presence of a denaturing reagent.