Structural Analysis of the Interaction of the Functional Amyloid Forming Protein Orb2A with Lipids

Abstract

Orb2 is a CPEB homologue in fruit flies involved in regulation of mRNA translation at the synapse and is essential for stabilization of long term memory. This function is accomplished by the aggregation of Orb2 into amyloid-like oligomers. There are two isoforms of Orb2: Orb2A and Orb2B, and both are found in the aggregates together. However, while Orb2B is constitutively expressed, Orb2A expression is rare and necessary for Orb2 to form aggregates in vivo. This suggests that Orb2A is a main regulator of initiation of fibril formation. This study focuses on Orb2A lipid interaction, a potential mechanism by which Orb2A initiates aggregation. Orb2A is found enriched in the membrane fraction of the synapse, and sequence analysis reveals the possibility of an amphipathic helix present in the unique N-terminus of Orb2A. The aggregation of several other amyloids, including IAPP, Pmel17, and Aβ, has been shown to be regulated by lipids. I hypothesize that such a mechanism could also be utilized by Orb2A to either inhibit or induce amyloid formation. I use circular dichroism, electron paramagnetic resonance, and solid-state NMR of Orb2A deletion mutants to explore the effects of the interaction of Orb2A with lipid bilayers. We show that structural changes do occur upon lipid addition and identify the region involved in these structural changes.