The inhibitory action of phospholamban involves stabilization of α-helices within the Ca-ATPase

We have used attenuated total reflection Fourier transform infrared (ATR-FTIR) and circular dichroism (CD) spectroscopies to identify secondary and dynamic structural changes within the Ca-ATPase that result from the functional inhibition of transport activity by phospholamban (PLB). Isotopically labeled [C-13]PLB was expressed and purified from Escherichia coli and was functionally reconstituted with unlabeled Ca-ATPase, permitting the resolution: of the amide I and II absorbance bands of the Ca-ATPase from those of [C-13]PLB. Upon co-reconstitution of the Ca-ATPase with PLB, spectral shifts are observed in both the CD spectra and the amide I and II bands associated with the Ca-ATPase, which are indicative of increased alpha-helical stability. Corresponding changes in the kinetics of H/D exchange occur upon association with PLB, indicating that 100 20 residues in the Ca-ATPase that normally undergo rapid amide H/D exchange become exchange resistant. There are no corresponding large changes in the secondary structure of PLB. The affinity of the structural interaction between PLB and the Ca-ATPase is virtually identical to that associated with functional inhibition (K-d = 140 +/- 30 muM), confirming that the inhibitory regulation of the Ca-ATPase by PLB involves the stabilization of alpha-helices within the Ca-ATPase.