Low-complexity (LC) domains of RNA-binding proteins are crucial for protein functions, including gene expression and mRNA processing. However, aberrant aggregation of LC domains into amyloid fibrils, which may occur within phase-separated liquid droplets, is known to be connected to neurodegenerative diseases such as ALS and FTD. Interestingly, unlike other pathological amyloid-forming proteins such as Aβ and α-synuclein, LC domains are relatively devoid of hydrophobic residues, which play important roles in stabilizing the amyloid fibril core. Thus, it is largely unknown how LC domains form amyloid fibrils.<br/>The molecular structure of fibrils formed by the 214-residue LC domain of the fused in sarcoma (FUS LC) RNA-binding protein had shown that the fibril core is formed by the N-terminal 57-residues, while the C-terminal half (FUS LC-C) remains highly flexible. However, surprisingly, we found that FUS LC-C forms fibrils when the N-terminal half (FUS LC-N) is deleted. Thus, we used cryo-electron microscopy (cryoEM) and solid-state NMR (ssNMR) to study the molecular structure of the FUS LC-C fibrils to understand the molecular interactions that drive the FUS LC-C fibril formation without the N-terminal core.<br/>The molecular structural model for FUS LC-C fibrils based on the high-resolution cryoEM density map shows that the fibril core comprised of residues 112-150 adopts a U-shaped conformation and contains two subunits with parallel in-register cross β-structures. 2D INEPT spectra measured under solution NMR conditions show that the C-terminal region of FUS LC-C (residues 151-214) is dynamically disordered. By performing molecular dynamics simulations on the structural model, we found that the fibril core is stabilized by multiple hydrogen bonds among Gln, Ser, and Tyr residues with varying populations, including sidechain-sidechain and sidechain-backbone hydrogens within and between FUS LC-C molecules. These results offer a structural basis for the nature of molecular interactions that drive the self-assembly and the fibril formation by a disordered LC sequence.

FUS low complexity domain fibril structure by cryo-electron microscopy and solid-state NMR

ACS Spring Meeting 2021

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.