Cryo-EM structures of pathogenic fibrils and their impact on neurodegenerative disease research.

Neurodegenerative diseases are commonly associated with the formation of aberrant protein aggregates within the brain, and ultrastructural analyses have revealed that the proteins within these inclusions often assemble into amyloid filaments. Cryoelectron microscopy (cryo-EM) has emerged as an effective method for determining the near-atomic structure of these disease-associated filamentous proteins, and the resulting structures have revolutionized the way we think about aberrant protein aggregation and propagation during disease progression. These structures have also revealed that individual fibril conformations may dictate different disease conditions, and this newfound knowledge has improved disease modeling in the lab and advanced the ongoing pursuit of clinical tools capable of distinguishing and targeting different pathogenic entities within living patients. In this review, we summarize some of the recently developed cryo-EM structures of ex vivo α-synuclein, tau, ß-amyloid (Aß), TAR DNA-binding protein 43 (TDP-43), and transmembrane protein 106B (TMEM106B) fibrils and discuss how these structures are being leveraged toward mechanistic research and therapeutic development.

In Silico Investigation of Parkin-Activating Mutations Using Simulations and Network Modeling.

Complete loss-of-function mutations in the PRKN gene are a major cause of early-onset Parkinson's disease (PD). PRKN encodes the Parkin protein, an E3 ubiquitin ligase that works in conjunction with the ubiquitin kinase PINK1 in a distinct quality control pathway to tag damaged mitochondria for autophagic clearance, i.e., mitophagy. According to previous structural investigations, Parkin protein is typically kept in an inactive conformation via several intramolecular, auto-inhibitory interactions. Here, we performed molecular dynamics simulations (MDS) to provide insights into conformational changes occurring during the de-repression of Parkin and the gain of catalytic activity. We analyzed four different Parkin-activating mutations that are predicted to disrupt certain aspects of its auto-inhibition. All four variants showed greater conformational motions compared to wild-type protein, as well as differences in distances between domain interfaces and solvent-accessible surface area, which are thought to play critical roles as Parkin gains catalytic activity. Our findings reveal that the studied variants exert a notable influence on Parkin activation as they alter the opening of its closed inactive structure, a finding that is supported by recent structure- and cell-based studies. These findings not only helped further characterize the hyperactive variants but overall improved our understanding of Parkin's catalytic activity and nominated targets within Parkin's structure for potential therapeutic designs.

HDGFL2 cryptic proteins report presence of TDP-43 pathology in neurodegenerative diseases.

This letter demonstrates the potential of novel cryptic proteins resulting from TAR DNA-binding protein 43 (TDP-43) dysfunction as markers of TDP-43 pathology in neurodegenerative diseases.

Statistical Mechanics Metrics in Pairing and Parsing In Silico and Phenotypic Data of a Novel Genetic NFκB1 (c.T638A) Variant.

(1) Background: Mutations in NFκB1, a transcriptional regulator of immunomodulating proteins, are a known cause of inborn errors of immunity. Our proband is a 22-year-old male with a diagnosis of common variable immunodeficiency (CVID), cytopenias with massive splenomegaly, and nodular regenerative hyperplasia of the liver. Genetic studies identified a novel, single-point mutation variant in NFκB1, c. T638A p. V213E. (2) Methods: Next-generation panel sequencing of the patient uncovered a novel single-point mutation in the NFκB1 gene that was modeled using the I-TASSER homology-modeling software, and molecular dynamics were assessed using the YASARA2 software (version 20.14.24). (3) Results: This variant replaces valine with glutamic acid at position 213 in the NFκB1 sequence. Molecular modeling and molecular dynamic studies showed altered dynamics in and around the rel homology domain, ankyrin regions, and death domain of the protein. We postulate that these changes alter overall protein function. (4) Conclusions: This case suggests the pathogenicity of a novel variant using protein-modeling techniques and molecular dynamic simulations.

Molecular dynamics simulations of the flexibility and inhibition of SARS-CoV-2 NSP 13 helicase.

The helicase protein of the Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) is both a good potential drug target and very flexible. The flexibility, and therefore its function, could be reduced through knowledge of these motions and identification of allosteric pockets. Using molecular dynamics simulations with enhanced sampling, we determined key modes of motion and sites on the protein that are at the interface between flexible domains of the proteins. We developed an approach to map the principal components of motion onto the surface of a potential binding pocket to help in the identification of allosteric sites.

Coarse-Grained Models for Constant pH Simulations of Carboxylic Acids.

A model for carboxylic acids, in both the protonated and deprotonated states, is developed in which hydrogen interaction sites are not used and all interactions are short-ranged. A method for constant pH simulations, which exploits these features of the model, is developed. The constant pH method samples protonation states by making discrete Monte Carlo steps and is able to efficiently move between states in two steps. The method is applied to the polymer poly(methacrylic acid), a pH-responsive polymer that undergoes structural changes as a function of pH. The model is able to reproduce the structural changes induced by pH.