Public defence, Biotechnology, MSc Mengjie Shen

Title of the thesis: Phase-separation mediated self-assembly as a route to protein-based biomaterials

Thesis defender: Mengjie Shen
Opponent: Prof. Jan K. Rainey, Dalhousie University, Canada
Custos: Prof. Sesilja Aranko, Aalto University School of Chemical Engineering

Nature produces a wide range of protein-based materials with remarkable properties, from strong spider silk to collagen-rich structures. These materials form through the self-assembly of proteins, but reproducing and controlling these processes in the laboratory remains challenging. A better understanding of how proteins organize and assemble could help researchers develop new materials from renewable biological building blocks.

Liquid–liquid phase separation (LLPS) has attracted growing interest as a process that may influence protein assembly. It occurs when a homogeneous solution separates into two liquid phases: one in which proteins are concentrated and another in which their concentration is lower. LLPS plays a role in the organization of biological molecules and has also been explored as a way to influence the formation of protein-based materials.

In this doctoral research, two model protein systems inspired by natural materials were investigated: collagen-like proteins and spider-silk-like proteins. The collagen-like proteins were used to study how phase separation relates to triple-helix formation, structural stability and the assembly of larger protein structures. The spider-silk-like proteins were used to examine how polymer length affects phase-separation behavior.

The results showed that phase separation can facilitate the assembly of recombinant collagen-like proteins into triple-helical structures and higher-order assemblies. Differences in the proteins’ physicochemical properties were associated with differences in their phase-separation behavior and thermal stability. The study also showed that polymer length influences phase-separation behavior, including the conditions required for phase separation and the properties of the resulting protein-rich droplets.

Together, these findings improve our understanding of how protein characteristics influence phase separation and assembly. In the longer term, this knowledge may help researchers better understand and control the formation of protein-based materials, supporting the development of materials with properties tailored for different purposes.

Thesis available for public display 7 days prior to the defence at Aalto University's public display page.