Aggregation Kinetics and Filament Structure of a Tau Fragment Are Influenced by the Sulfation Pattern of the Cofactor Heparin.

David Townsend,Nigel J Fullwood,Edwin A Yates,David A Middleton

doi:10.1021/acs.biochem.0c00443

David Townsend, Nigel J Fullwood + Show 2 more

Open Access

https://doi.org/10.1021/acs.biochem.0c00443

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Abstract

A pathological signature of Alzheimer’s disease (AD) is the formation of neurofibrillary tangles comprising filamentous aggregates of the microtubule associated protein tau. Tau self-assembly is accelerated by polyanions including heparin, an analogue of heparan sulfate. Tau filaments colocalize with heparan sulfate proteoglycans (HSPGs) in vivo, and HSPGs may also assist the transcellular propagation of tau aggregates. Here, we investigate the role of the sulfate moieties of heparin in the aggregation of a recombinant tau fragment Δtau187, comprising residues 255–441 of the C-terminal microtubule-binding domain. The effects that the selective removal of the N-, 2-O-, and 6-O-sulfate groups from heparin have on the kinetics of tau aggregation, aggregate morphology, and protein structure and dynamics were examined. Aggregation kinetics monitored by thioflavin T (ThT) fluorescence revealed that aggregation is considerably slower in the presence of 2-O-desulfated heparin than with N- or 6-O-desulfated heparin. Transmission electron microscopy revealed that tau filaments induced by 2-O-desulfated heparin were more slender than filaments formed in the presence of intact heparin or 6-O-desulfated heparin. The 2-O-desulfated heparin-induced filaments had more extensive regions of flexibility than the other filaments, according to circular dichroism and solid-state NMR spectroscopy. These results indicate that the sulfation pattern of heparin regulates tau aggregation, not purely though electrostatic forces but also through conformational perturbations of heparin when the 2-O-sulfate is removed. These findings may have implications for the progression of AD, as the sulfation pattern of GAGs is known to change during the aging process, which is the main risk factor for the disease.

Highlights

Sulfate groups from heparin have on the kinetics of tau aggregation, aggregate morphology, and protein structure and dynamics were examined
It has often been assumed that heparin−tau interactions are driven largely by nonspecific ionic interactions between the protein and the sulfate and carboxylate groups of heparin,[16] but this notion has been challenged by recent results showing that the sulfation pattern of HS influences the cellular internalization of tau, with the 6-O-sulfate being critical for this process and for tau binding.[17−19] Here, using selectively desulfated heparin molecules, we show that the sulfation pattern of heparin influences the rate of aggregation of a truncated tau construct and modulates the mass, nanoscale morphology, and atomic structure of the filaments formed
Heparan sulfate, and heparan sulfate proteoglycans (HSPGs) such as agrin are commonly associated with Aβ plaques and

Summary

Introduction

Sulfate groups from heparin have on the kinetics of tau aggregation, aggregate morphology, and protein structure and dynamics were examined. The 2-O-desulfated heparin-induced filaments had more extensive regions of flexibility than the other filaments, according to circular dichroism and solid-state NMR spectroscopy These results indicate that the sulfation pattern of heparin regulates tau aggregation, not purely though electrostatic forces and through conformational perturbations of heparin when the 2-O-sulfate is removed. It is worth noting, that there is insufficient information about the structural variability of filaments obtained from different AD or Pick’s brains, given the limited current data and challenges involved. The residual sulfate levels of the 6-O- and 2-O- desulfated LMW heparin derivatives are 61 and 70% and of the HMW heparin derivatives are 50 and 42% of the sulfate levels of the respective unmodified heparin, as measured by enzymatic digestion followed by highperformance anion exchange chromatography (HPAEC)

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