Nano-scale Properties of the Amyloid Life-Cycle

Speaker: Wei-Feng Xue
Department: School of Biosciences, University of Kent
Subject: Nano-scale Properties of the Amyloid Life-Cycle
Location: TU Delft
Date: May 16, 2016

author: Teun Huijben

Amyloid are fibrillar structures that have a width of approximately ten nanometers and are formed from proteins or peptides. They can be made from a wide variety of monomers, can differ a lot in length and can have many different functions. People started doing research on amyloid when they found out that prions (transmissible amyloid) had a lot to do with diseases like Scrapie, Creutzfeldt-Jakob and the Mad Cow Disease. These days still a lot of research in going on in this field, not only to get a better understanding of the structure and function of amyloid, but also because of its interesting mechanical properties like strength and elasticity.

As already stated, there are many different types of amyloid and they can be formed by the assembly of a wide variety of monomers. This is mainly the reason why its function is not well understood, because amyloid has so many different forms. A common thing in the structure of the fibrils is that they exist of many β-sheets that are connected in a parallel fashion orthogonal to the propagation axis of the fibrils. But knowing that this molecular structure determines the shape and properties of the complex, this is not the area of interest for Wei-Feng Xue. Who is doing research on amyloid for over 10 years and is currently working at the University of Kent (UK).

Mr. Xue is more interested in how amyloid is formed, how it forms toxic structures and how it is nucleated, growing and fragmented. After doing a lot of research on amyloid his current hypothesis is that amyloid has a certain life-cycle (see figure 1 below). This life-cycle starts with the primary nucleation of monomers to form short fibrils. This short fibrils grow by elongation and can later be fragmented into shorter pieces that can spread and elongate to form new fibrils. He is fascinated by the great distribution in length of amyloid fibers and what this variety has for influence on its function. A lot of different aspects of amyloid are studied in his lab and he gave us a brief overview of things that are going on  there.

Schermafbeelding 2016-05-12 om 21.21.02figure 1: suggested life-cycle of Amyloid. The circles represent monomers and the arrows represent steps in the life-cycle. The cycle starts with nucleation (red and purple), then the fibrils are elongated (blue) and fragmented (yellow) to start new fibrils. 

Amyloid fibers are twisted and one thing they are looking at is what the precise structure is and what influences this structure. With atomic force microscopy (AFM) pictures are made of the fibrils and this data is analyzed by home-made MatLab software. From this data they make models of the structure and how the fibrils are twisted around each other.

Another major theme in his research on amyloid is the fragmentation of fibrils. When the fibrils have some length they get fragmented into shorter pieces and these pieces can grow into new fibrils. Their hypothesis is that fragmentation speeds up the growing of fibrils, because other experiments have shows that short fibrils elongate faster than long fibrils. To do in vitro experiments on fragmentation a solution of fibrils is mixed with a magnetic stirrer that brutally breaks the fibrils in pieces. When more force was applied, the average length of fibrils got shorter and the length distribution more narrow. This indicates that short fibrils are more stable. Now they are testing different types of amyloid and plot persistence length versus fragmentation constant. They hope to see distinct groups, what will give more insight in the mechanical properties and functions of the fibrils. The same things are measured in vivo, but then enzymes are used to cut the fibrils instead of using brute force.

The most recent thing they are doing right now is producing synthetic prions and insert them into yeast cells. Then with a colorimetric assay is tested if the prion is in its toxic prion-form or not. The goal is to find characteristics of amyloid fibrils that make them more likely to become a dangerous prion and getting more insight in the toxicity of amyloid fibers. And I think this is very necessary to do, because still a lot is unclear about prions; how they cause diseases and how to prevent them from doing that.

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