Journal News

JBC: How do protein tangles get so long?

Laurel Oldach
June 1, 2019

Long before Alzheimer’s disease patients notice any symptoms, neurofibrillary tangles composed of tau protein filaments begin to form in their brain cells. How toxic these aggregates are and how well they spread depend on their size — that is, the number of tau monomers they contain. However, scientists studying tangle formation have not been able to explain why different sizes of tau aggregates appear in disease.

But now researchers have discovered that instead of adding just one protein at a time, fibrils of various lengths can join end-to-end to create one larger filament. The finding, published in the Journal of Biological Chemistry, helps explain how fibrils can grow to hundreds of nanometers. It also could help researchers understand mechanisms of an emerging group of drug candidates designed to inhibit tau aggregation.

A common simple model of tau aggregation and fibril formation includes two steps. First, two tau proteins bind slowly; additional tau molecules latch on quickly.

Carol Huseby, then a graduate student in Jeff Kuret’s lab at THE Ohio State University, worked with Ralf Bundschuh to expand this mathematical model to include other known ways that tau fibrils behave. Scientists have observed, for example, that sometimes one fibril fragments into two. Or a new fibril can nucleate in the middle of an existing fibril.

Tau proteins labeled with three fluorescent dyesTau proteins labeled with three fluorescent dyes were allowed to aggregate in separate test tubes, shown in the three images at left. The different colored fibrils were mixed in a fourth test tube, at right, resulting in long fibrils with short sections of each color. Carol Huseby/The Ohio State University
The simple model predicted many short fibrils. But Huseby knew that, under a microscope, aggregated tau appears as a smaller number of long fibrils. That discrepancy suggested that something was happening in the real world that hadn’t been accounted for in the model. They hypothesized that short fibrils could attach end-to-end to get longer.

To test the hypothesis, Huseby labeled tau proteins with three fluorescent colors and allowed them to aggregate in separate test tubes. Then she mixed the different colored fibrils in a fourth test tube.

Images taken with a super-resolution fluorescence microscope showed long fibrils with short sections of each color, indicating that fibrils from the original test tubes had joined ends to form longer fibrils. Control experiments established that this can’t be explained by labeled molecules’ preference for like labels.

After Huseby incorporated this new mechanism into the model, it produced a better description of what purified tau proteins were doing as they formed aggregates. This study is the first to show that the fibrils can elongate by more than a single tau protein at a time.

Alzheimer’s disease researchers still are trying to discern whether tau fibrils are a cause or simply an effect of the disease. Transmission of fibrils from one cell to another may contribute to the spread of disease in the brain. A very long fibril, according to Kuret, is unlikely to spread in this way. “But once it’s broken up into little pieces, those can diffuse,” he said, “facilitating their movement from cell to cell.”

This study used just one type of tau. Six isoforms are known, and phosphorylation and other changes increase the protein’s complexity. The researchers plan to incorporate these variables in future work and to use the model to understand how tau inhibitors change the protein aggregates’ behavior.

Enjoy reading ASBMB Today?

Become a member to receive the print edition four times a year and the digital edition monthly.

Learn more
Laurel Oldach

Laurel Oldach is a former science writer for the ASBMB.

Get the latest from ASBMB Today

Enter your email address, and we’ll send you a weekly email with recent articles, interviews and more.

Latest in Science

Science highlights or most popular articles

AI-designed biomarker improves malaria diagnostics
Journal News

AI-designed biomarker improves malaria diagnostics

Oct. 8, 2025

Researchers from the University of Melbourne engineered Plasmodium vivax diagnostic protein with enhanced yield and stability while preserving antibody-binding, paving the way for more reliable malaria testing.

Matrix metalloproteinase inhibitor reduces cancer invasion
Journal News

Matrix metalloproteinase inhibitor reduces cancer invasion

Oct. 8, 2025

Scientists at the Mayo Clinic engineered a TIMP-1 protein variant that selectively inhibits MMP-9 and reduces invasion of triple-negative breast cancer cells, offering a promising tool for targeted cancer research.

Antibiotic sensor directly binds drug in resistant bacteria
Journal News

Antibiotic sensor directly binds drug in resistant bacteria

Oct. 8, 2025

Researchers at Drexel University uncover how the vancomycin-resistant bacterial sensor binds to the antibiotic, offering insights to guide inhibitor design that restores antibiotic effectiveness against hospital-acquired infections.

ApoA1 reduce atherosclerotic plaques via cell death pathway
Journal News

ApoA1 reduce atherosclerotic plaques via cell death pathway

Oct. 1, 2025

Researchers show that ApoA1, a key HDL protein, helps reduce plaque and necrotic core formation in atherosclerosis by modulating Bim-driven macrophage death. The findings reveal new insights into how ApoA1 protects against heart disease.

Omega-3 lowers inflammation, blood pressure in obese adults
Journal News

Omega-3 lowers inflammation, blood pressure in obese adults

Oct. 1, 2025

A randomized study shows omega-3 supplements reduce proinflammatory chemokines and lower blood pressure in obese adults, furthering the understanding of how to modulate cardiovascular disease risk.

AI unlocks the hidden grammar of gene regulation
Feature

AI unlocks the hidden grammar of gene regulation

Sept. 30, 2025

Using fruit flies and artificial intelligence, Julia Zeitlinger’s lab is decoding genome patterns — revealing how transcription factors and nucleosomes control gene expression, pushing biology toward faster, more precise discoveries.