Biology subjects

James, E. I.

Publications and source records attributed to James, E. I..

3 recordsLinked to original sources

bioRxiv2025

Tau4RD fibril polymorphism is imprinted during early aggregation

Microtubule-associated protein tau forms characteristic fibrillar species in many neurodegenerative diseases. Neurofibrillary tangles, tau deposits observed in Alzheimers disease (AD), contain a mixture of amyloid-type polymorphic fibrils called paired helical filaments (PHFs) and straight filaments. The formation of heterogenous fibril populations is observed in other diseases and when tau aggregation is induced in vitro with polyanionic species. This suggests that taus structural transition from a conformational ensemble to various amyloid morphologies is a controlled and, therefore, controllable process. Despite many years of work toward describing aggregation intermediates that could address open questions such as whether fibril polymorphism is imprinted at the start of aggregation or arises due to conformational conversions, our understanding of amyloid structure remains predominantly based on observations of mature fibrils. It is unclear whether these processes are mutually exclusive and to what extent we can bias intermediate conformations toward less toxic states. Here to address the challenge of studying aggregation intermediates and taus structural conversion, we apply pulsed hydrogen-deuterium exchange with mass spectrometry (pulsed HDX-MS), which revealed differences in the subpopulations formed by tau4RD (a truncated tau construct) within seconds of initiating aggregation with polyphosphate and within hours of heparin-induction. This work begins to address the gap in knowledge regarding whether amyloid polymorphism is directly imprinted during nucleation or results from structural rearrangement during later stages of aggregation.

biophysics↗

bioRxiv2024

Tryptanthrin Analogs Substoichiometrically Inhibit Seeded and Unseeded Tau4RD Aggregation

Microtubule-associated protein tau is an intrinsically disordered protein (IDP) that forms characteristic fibrillar aggregates in several diseases, the most well-known of which is Alzheimers disease (AD). Despite keen interest in disrupting or inhibiting tau aggregation to treat AD and related dementias, there are currently no FDA-approved tau-targeting drugs. This is due, in part, to the fact that tau and other IDPs do not exhibit a single well-defined conformation but instead populate a fluctuating conformational ensemble that precludes finding a stable "druggable" pocket. Despite this challenge, we previously reported the discovery of two novel families of tau ligands, including a class of aggregation inhibitors, identified through a protocol that combines molecular dynamics, structural analysis, and machine learning. Here we extend our exploration of tau druggability with the identification of tryptanthrin and its analogs as potent, substoichiometric aggregation inhibitors, with the best compounds showing potencies in the low nanomolar range even at a [~]100-fold molar excess of tau4RD. Moreover, conservative changes in small molecule structure can have large impacts on inhibitory potency, demonstrating that similar structure-activity relationship (SAR) principles as used for traditional drug development also apply to tau and potentially to other IDPs.

biochemistry↗

bioRxiv2022

HSPB5 disease-associated mutations have long-range effects on structure and dynamics through networks of quasi-ordered interactions

Found from bacteria to humans, small heat shock proteins (sHSPs) are the least understood protein chaperones. HSPB5 (or B-crystallin) is among the most widely expressed of the ten human sHSPs, including in muscle, brain, and eye lens where it is constitutively present at very high levels and carries out a myriad of functions. A high content of disorder in HSPB5 has stymied efforts to uncover how its structure gives rise to function. To uncover its mechanisms of action, we compared human HSPB5 and two disease-associated mutants, R120G and D109H. Expecting to learn how the mutations lead to loss of function, we found instead that the mutants are constitutively activated chaperones while wild-type HSPB5 can transition reversibly between non-activated (low activity) and activated (high activity) states in response to changing conditions. Techniques that provide information regarding interactions and accessibility of disordered regions revealed that the disordered N-terminal regions (NTR) that are required for chaperone activity exist in a complicated interaction network within HSPB5 oligomers and are sequestered from solvent in non-activated states. Either mutation or an activating pH change cause rearrangements in the network that expose parts of the NTR, making them more available to bind an aggregating client. While beneficial in the short-term, failure of the mutants to adopt a state with lower activity and lower NTR accessibility leads to increased co-aggregation propensity and, presumably, early cataract. The results support a model where chaperone activity and solubility are modulated through the quasi-ordered NTR and its multiple competing interactions. SignificanceSmall heat shock proteins (sHSPs) are the oldest known protein chaperones, but how they recognize misfolding proteins in early stages of aggregation is unknown. Disordered regions within sHSPs are critical to their function, raising the question of how disorder recognizes disorder. We investigated a human sHSP (HSPB5) and two disease mutants using approaches that provide residue-level information in regions of disorder. The findings reveal that large, heterogeneous oligomers of HSPB5 contain complicated networks of interactions involving their disordered regions that protect them from solvent. Conditions associated with stress or disease mutations cause a rearrangement of the interaction network and enhancement of chaperone activity. The study provides new information regarding how disordered regions are modulated in a network of competing interactions.

biophysics↗