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

Area of Science:

• Neuroscience
• Biochemistry
• Structural Biology

Background:

• The prion-like domain (PLD) of Drosophila Orb2A protein is implicated in memory consolidation through amyloid formation.
• Previous studies elucidated the structure of ex vivo Orb2 fibrils but lacked atomic-level details on conformational transitions.

Purpose of the Study:

• To characterize the nascent conformation and dynamics of the Orb2A PLD.
• To investigate the influence of pH and metal ion binding on Orb2A PLD structure and self-association.

Main Methods:

• Utilized a nonconventional liquid-state NMR spectroscopy strategy with 13C detection.
• Obtained comprehensive 13Cα, 13Cβ, 1Hα, and backbone 13CO/15N assignments.
• Investigated protein behavior at pH 4 and pH 7, including RNA and metal ion (Ca2+, Zn2+) interactions.

Main Results:

• At pH 4, Orb2A PLD is disordered with a minor α-helix (residues 55-60) and binds RNA but not divalent cations.
• At pH 7, His residues are neutral, leading to minor helical structures, reduced mobility, and initial self-association.
• Zinc (Zn2+) binding at pH 7 promotes further self-association, while RNA and calcium (Ca2+) do not bind.

Conclusions:

• Orb2A PLD displays significant structural plasticity, adapting its conformation and interactions based on pH and metal ion availability.
• An updated model for Orb2A functional amyloidogenesis is proposed, highlighting the role of pH-dependent histidine protonation and zinc-mediated self-association in memory mechanisms.