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‘Bacterial builders’ produce functional biomaterials

Investigating a method for forming genetically-engineered, customizable protein structures directly from bacterial culture

A team of Wyss Institute researchers has revealed a novel, efficient and scalable method for building biomaterials – using E. coli bacterial colonies as biofactories – from protein structures called ‘amyloids’.

Amyloids are naturally occurring fibrous structures that have nanometer size features, and are associated with a range of biological functions. They were originally thought to be hallmarks of Alzheimer’s and Parkinson’s diseases triggered by protein misfolding, but more recently, “functional amyloids” were discovered to play beneficial roles in the protection of organisms and in their interaction with surfaces, including insects and bacteria.

A new vacuum filtration method developed by Neel Joshi’s team allows free-standing protein structures, such as the film pictured here on the left, to be produced in bacterial broth culture and then quickly and affordably separated from the broth. On the right, a scanning electron micrograph of such an amyloid film shows the imprint of pores left behind by the filtration membrane used to separate it from bacterial broth culture. Credit: Wyss Institute at Harvard University

At the same time, materials scientists have been interested in amyloid fibers as a powerful platform for building biomaterials due to their molecular self-assembly. Amyloid biomaterials have already been used in applications ranging from water purification to vaccines and tissue engineering.

However, despite their many useful features, there has not yet been a way to synthesize customized amyloid proteins in large enough quantities to make them practical building blocks for scalable materials. Conventional approaches to amyloid-based materials fabrication either rely on protein components isolated from natural sources, which are difficult to customize for particular applications, or they require time consuming and costly purification after recombinant production in a microbial host like E. coli.

A team led by Wyss Core Faculty member Neel Joshi, Ph.D., has designed a streamlined, vacuum filtration method that enables fast separation of amyloid fibers from E. coli broth cultures.  Their technique relies on the ability of a particular class of amyloid fibers to remain intact even in the presence of harsh detergents and enzymes that will break down cells, DNA and other proteins. Notably, it requires no specialized equipment and circumvents the need for slow purification steps. Their findings, which were reported in October 2016 in ACS Biomaterials Science and Engineering, represent an efficient simplification of existing approaches to protein-based materials fabrication and also improve protein yields by an order of magnitude compared to previous techniques.

The vacuum filtration method developed by Joshi and postdoctoral researchers Noémie-Manuelle Dorval Courchesne and Anna Duraj-Thatte allows for E. coli’s manufacturing system to be harnessed and modified to produce biomaterials with specified shapes and sizes and useful properties, including the ability to sequester and remove individual chemicals from complex mixtures, to act as an adhesive between two biological surfaces, or to provide signals to biological tissues.

“Our method makes highly customized materials built from recombinant proteins accessible to anybody who can culture bacteria and perform filtration,” said Joshi, who is also Associate Professor of Chemical and Biological Engineering at the Harvard John A. Paulson School of Engineering and Applies Sciences.

So far, Joshi’s team has demonstrated formation of free-standing thin films via vacuum filtration. Ongoing work in the lab is focused on fabricating a wide variety of materials, including customized affinity matrices designed to separate a single species from complex mixtures, and hydrogels that can interface with the body.

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