Ca²⁺ and Mg²⁺ modulate conformational dynamics and stability of downstream regulatory element antagonist modulator

Abstract

Downstream Regulatory Element Antagonist Modulator (DREAM) belongs to the family of neuronal calcium sensors (NCS) that transduce the intracellular changes in Ca 21 concentration into a variety of responses including gene expression, regulation of Kv channel activity, and calcium homeostasis. Despite the significant sequence and structural similarities with other NCS members, DREAM shows several features unique among NCS such as formation of a tetramer in the apo-state, and interactions with various intracellular biomacromolecules including DNA, presenilin, Kv channels, and calmodulin. Here we use spectroscopic techniques in combination with molecular dynamics simulation to study conformational changes induced by Ca 21 /Mg 21 association to DREAM. Our data indicate a minor impact of Ca 21 association on the overall structure of the Nand C-terminal domains, although Ca 21 binding decreases the conformational heterogeneity as evident from the decrease in the fluorescence lifetime distribution in the Ca 21 bound forms of the protein. Time-resolved fluorescence data indicate that Ca 21 binding triggers a conformational transition that is characterized by more efficient quenching of Trp residue. The unfolding of DREAM occurs through an partially unfolded intermediate that is stabilized by Ca 21 association to EF-hand 3 and EF-hand 4. The native state is stabilized with respect to the partially unfolded state only in the presence of both Ca 21 and Mg 21 suggesting that, under physiological conditions, Ca 21 free DREAM exhibits a high conformational flexibility that may facilitate its physiological functions.

Molecular insight of DREAM and presenilin 1 C‐terminal fragment interactions

“…To understand the mechanism of how Ca 2+ regulates DREAM and PS1‐CTF interactions, the structure of Ca 2+ DREAM was superposed with the model structure of ApoDREAM (Fig. S3) . In the ApoDREAM structure, the aromatic ring of F252 rotates ~ 90° preventing π–π stacking with aromatic rings of F462 and F465 from PS1 and destabilizing the aromatic cluster between phenylalanine residues from DREAM and PS1‐CTF.…”

Conformational Dynamics and Stability Associated with Magnesium or Calcium Binding to DREAM in the Regulation of Interactions between DREAM and DNA or Presenilins

“…Alternatively, advances of molecular dynamics (MD) simulations provide a comprehensive approach to model the structures of proteins (Hospital et al, 2015). These results are in agreement with that observed from the previous MD simulation study in our group (Pham, Dhulipala et al 2015) and the NMR study reported by Lusin et al (Lusin et al, 2008), indicating that the force field (CHARMM27) and the MD …”

“…However, no significant changes in the protein secondary or tertiary structure takes place due to the Mg 2+ association to EF-hand 2, as evident from the absence of W169 emission enhancement and/or increase in the α-helical contain upon Mg 2+ association to ApoDREAM (Osawa et al, 2005;Lusin et al, 2008;Pham et al 2015;Gonzalez et al, 2016).…”

Characterization of the Photophysical, Thermodynamic, and Structural Properties of the Terbium(III)–DREAM Complex

“…Using molecular dynamics, we have previously shown that Trp169 in DREAM(Δ64) can populate two rotamers, and it is possible that Tb 3+ binding could enhance this rotamer transition, which would result in an increase in local dynamics. 43 …”