Researchers say new development should help them map a treatment for the neurodegenerative disease.
Scientists have for the first time revealed the atomic structure of the tau protein filaments that tangle in the brains of Alzheimer's patients and say it should point the way towards developing new treatments for the disease.
Using a technique known as cryo-electron microscopy, a team from Britain's Medical Research Council Laboratory of Molecular Biology mapped in fine detail the tau filaments extracted from the brain of a patient who had died with Alzheimer's.
The most common neurodegenerative disease, Alzheimer's is characterized by two types of abnormal protein which form lesions or clumps in the brain. Tau forms filaments inside nerve cells and amyloid-beta forms filaments outside.
In healthy brains tau protein normally helps brain cells to function but in the brains of people with Alzheimer's disease tau clumps up in tangles inside the cells.
"Knowing which parts of tau are important for filament formation is relevant for the development of drugs," said Sjors Scheres, who co-led the research.
Since many pharmaceutical companies are using different parts of tau to test the effect of potential drugs on filament formation, this new knowledge "should significantly increase the accuracy of such tests," he said.
Specialists not directly involved in the study, which was published in the journal Nature, said its findings would prove extremely important in future.
"This study could take us into a new era of drug design," said James Pickett, head of research at the Alzheimer's Society medical charity - although he noted it can take 10 to 15 years to develop new medicines from this early stage of discovery.
John Hardy, a professor of neuroscience at University College London said the work was a "tour de force" which "will help us understand the pathogenesis of Alzheimer's".