Dillard, L. | bioRxiv Science

bioRxiv2021

Distinct cryo-EM Structure of α-synuclein Filaments derived by Tau

Recent structural studies of ex vivo amyloid filaments extracted from human patients demonstrated that the ex vivo filaments associated with different disease phenotypes adopt diverse molecular conformations distinct from those in vitro amyloid filaments. A very recent cryo-EM structural study also revealed that ex vivo -synuclein filaments extracted from multiple system atrophy (MSA) patients adopt quite distinct molecular structures from those of in vitro -synuclein filaments, suggesting the presence of co-factors for -synuclein aggregation in vivo. Here, we report structural characterizations of -synuclein filaments derived by a potential co-factor, tau, using cryo-EM and solid-state NMR. Our cryo-EM structure of the tau-promoted -synuclein filament at 4.0 [A] resolution is somewhat similar to one of the polymorphs of in vitro -synuclein filaments. However, the N- and C-terminal regions of the tau-promoted -synuclein filament have different molecular conformations. Our structural studies highlight the conformational plasticity of -synuclein filaments, requiring additional structural investigation of not only more ex vivo -synuclein filaments, but also in vitro -synuclein filaments formed in the presence of diverse co-factors to better understand molecular basis of diverse molecular conformations of -synuclein filaments.

biochemistry↗

bioRxiv2020

Cryo-EM Structures of the SARS-CoV-2 Endoribonuclease Nsp15

New therapeutics are urgently needed to inhibit SARS-CoV-2, the virus responsible for the on-going Covid-19 pandemic. Nsp15, a uridine-specific endoribonuclease found in all coronaviruses, processes viral RNA to evade detection by RNA-activated host defense systems, making it a promising drug target. Previous work with SARS-CoV-1 established that Nsp15 is active as a hexamer, yet how Nsp15 recognizes and processes viral RNA remains unknown. Here we report a series of cryo-EM reconstructions of SARS-CoV-2 Nsp15. The UTP-bound cryo-EM reconstruction at 3.36 [A] resolution provides molecular details into how critical residues within the Nsp15 active site recognize uridine and facilitate catalysis of the phosphodiester bond, whereas the apo-states reveal active site conformational heterogeneity. We further demonstrate the specificity and mechanism of nuclease activity by analyzing Nsp15 products using mass spectrometry. Collectively, these findings advance understanding of how Nsp15 processes viral RNA and provide a structural framework for the development of new therapeutics.

biochemistry↗