Name | Mr. Samiol Azam |
---|---|
Organization | Florida International University |
Type | Poster |
Topic | Biophysical |
Title | Lead tightly associates with neuronal calcium sensor (NCS) protein DREAM and promotes structural changes analogous to calcium bound DREAM. |
Author(s) | Samiol Azam, Jaroslava Miksovska |
Author Location(s) | Florida International University, Miami, Fl, USA |
Abstract | Downstream regulatory element antagonist modulator (DREAM), is a 29kDa Ca2+ binding protein that controls several neurological processes including gene expression, apoptosis, and modulation of Kv4 voltage channels. Here we demonstrate that Pb2+ binds to EF-hands in DREAM with and equilibrium affinity higher that that determined for Ca2+. Pb2+ association triggers changes in the secondary and tertiary structure of the protein that are analogous to those observed in Ca2+ bound DREAM based on Trp 169 emission data and CD spectra. Namely, Pb2+ binding to DREAM leads to decrease of Trp 169 emission intensity and decrease in CD signal at 220nm. The hydrophobic cavity in the C-terminal domain of DREAM is solvent exposed in the presence of Pb2+ as determined using a hydrophobic probe 1, 8-ANS. The Kd values for 1,8-ANS binding to Ca2+ and Pb2+ bound DREAM were found to be similar; 73±10 μM and 103 ± 10 µM, respectively. Pb2+ binding to DREAM also modulates DREAM interactions with intracellular partners. For example, titrations of presenilin-1 with DREAM in the presence of Ca2+ or Pb2+ showed that Pb2+ bound DREAM has a similar affinity for presenilin-1 (Kd= 2.44±0.19 µM) as Ca2+ bound DREAM(Kd= 6.23 ± 1.60 µM). The impact of Pb2+ association on DREAM conformational dynamics was proved in time-resolved fluorescence studies and thermodynamics parameters for Pb2+ association to EF-hands were obtained using isothermal titration calorimetry (ITC). Those results indicate that DREAM and likely other neuronal calcium sensors may contribute to lead-induced toxicity. |