Title
Pb2+ Binds to DREAM and Modulates Its Interactions with Binding Partners: a Link between Neuronal Calcium Sensors and Pb2+ Neurotoxicity.
Author
Samiol Azam, Jaroslava Miksovska
Year
2018
Journal
ACS Chemical Neuroscience
Abstract
Pb2+ exposure leads to diverse neurological disorders; however, the mechanism of Pb2+-induced neurotoxicity is not clearly understood. Here we demonstrate that Pb2+ binds to EF-hands in DREAM (Downstream regulatory element antagonist modulator) with a lower equilibrium dissociation constant (Kd = 20 ± 2 nM) than Ca2+ (Kd = 1μM). Based on the Trp 169 emission and CD spectra, we report that Pb2+ association triggers changes in the protein secondary and tertiary structures that are analogous to those previously observed for Ca2+-bound protein. 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. Pb2+ association to DREAM also modulates interactions between DREAM and its intracellular partners as evident from the fact that Pb2+-bound DREAM associates to peptide-based model systems, presenilin-1 helix-9 “PS1HL9” and Kv4.3(70-90) “site-2” and Kv4.3(2-22) "site 1". Namely, dissociation constants for Pb2+-bound DREAM interaction with PS1HL9 (Kd = 2.4 ± 0.1 μM), site-2 (Kd = 11.0 ± 0.5 μM) and site 1 (Kd = 5.0 ± 0.6μM) are nearly identical to those observed for Ca2+ bound DREAM. Isothermal titration calorimetry data reveal that Pb2+ binds to two high affinity sites in Ca2+ bound DREAM with the overall apparent dissociation constant of 4.81 ± 0.06 μM and its binding to DREAM is entropy-driven. Taking into account the structural and sequence similarity between DREAM and other neuronal calcium sensor (NCS) proteins, these results strongly indicate that DREAM and possibly other NCS bind Pb2+ with a higher affinity than that for Ca2+ and Pb2+ interactions with NCS can contribute to the lead-induced neurotoxicity.
Instrument
J-810
Keywords
Circular dichroism, Secondary structure, Tertiary structure, Ligand binding, Biochemistry