Structural transitions in Orb2 prion-like domain relevant for functional aggregation in memory consolidation

Abstract

<jats:title>Abstract</jats:title><jats:p>The recent structural elucidation of <jats:italic>ex vivo Drosophila</jats:italic> Orb2 fibrils revealed a novel amyloid formed by interdigitated Gln and His residue side chains belonging to the prion-like domain. However, atomic-level details on the conformational transitions associated with memory consolidation remain unknown. Here, we have characterized the nascent conformation and dynamics of the prion-like domain (PLD) of Orb2A using a nonconventional liquid-state NMR spectroscopy strategy based on <jats:sup>13</jats:sup>C detection to afford an essentially complete set of <jats:sup>13</jats:sup>Cα, <jats:sup>13</jats:sup>Cβ, <jats:sup>1</jats:sup>Hα and backbone <jats:sup>13</jats:sup>CO and <jats:sup>15</jats:sup>N assignments. At pH 4, where His residues are protonated, the PLD is disordered and flexible, except for a partially populated α-helix spanning residues 55-60. At pH 7, in contrast, His residues are predominantly neutral and the Q/H segments adopt minor populations of helical structure, show decreased mobility and start to self-associate. At pH 7, the His residues also bind Zn<jats:sup>++</jats:sup>, which promotes further association. These findings represent a remarkable case of structural plasticity, based on which an updated model for Orb2A functional amyloidogenesis is advanced.</jats:p><jats:sec><jats:title>Highlights</jats:title><jats:p><jats:list list-type="bullet"><jats:list-item><jats:p>The Orb2 prion like domain that forms the structures related to memory consolidation is studied by solution NMR.</jats:p></jats:list-item><jats:list-item><jats:p>The amyloidogenic Q/H-rich stretch is disordered and flexible at low pH.</jats:p></jats:list-item><jats:list-item><jats:p>Residues 55-60 form a partly populated α-helix at pH 4.</jats:p></jats:list-item><jats:list-item><jats:p>At pH 7, the Q/H-rich segment also adopts a low population of α-helix and rigidifies.</jats:p></jats:list-item><jats:list-item><jats:p>Zn<jats:sup>++</jats:sup> binding induces associative changes in the Orb2 prion-like domain.</jats:p></jats:list-item></jats:list></jats:p></jats:sec>