文摘
Calmodulin (CaM) binds to the FERM domain of 80?kDa erythrocyte protein 4.1R (R30) independently of Ca2+ but, paradoxically, regulates R30 binding to transmembrane proteins in a Ca2+-dependent manner. We have previously mapped a Ca2+-independent CaM-binding site, pep11 (A264KKLWKVCVEHHTFFR), in 4.1R FERM domain and demonstrated that CaM, when saturated by Ca2+ (Ca2+/CaM), interacts simultaneously with pep11 and with Ser185 in A181KKLSMYGVDLHKAKD (pep9), the binding affinity of Ca2+/CaM for pep9 increasing dramatically in the presence of pep11. Based on these findings, we hypothesized that pep11 induced key conformational changes in the Ca2+/CaM complex. By differential scanning calorimetry analysis, we established that the C-lobe of CaM was more stable when bound to pep11 either in the presence or absence of Ca2+. Using nuclear magnetic resonance spectroscopy, we identified 8 residues in the N-lobe and 14 residues in the C-lobe of pep11 involved in interaction with CaM in both of presence and absence of Ca2+. Lastly, Kratky plots, generated by small-angle X-ray scattering analysis, indicated that the pep11/Ca2+/CaM complex adopted a relaxed globular shape. We propose that these unique properties may account in part for the previously described Ca2+/CaM-dependent regulation of R30 binding to membrane proteins.