Designing biosensor platforms to study glycosaminoglycan interactions
The importance of glycosaminoglycans (GAGs) has been highlighted in many areas of research during recent years. Not only are they important in providing structure and support to our tissues but they also function as interaction partners in the extracellular matrix and at the cell membrane. The chemical structure and most notably the high negative charge of GAGs give them unique and interesting features, but also makes studying GAG-related interactions challenging. Biofunctional immobilization of GAGs to surfaces opens up for the use of many surface sensitive techniques that could provide detailed information about how these molecules regulate tissue growth and maintenance as well as the development of diseases.
In this thesis, different methods for immobilizing GAGs to surfaces have been investigated with the aim of studying GAG-related interactions. Two surface modifications have been used: supported lipid bilayers and self-assembled monolayers, both having suitable qualities for molecular immobilization and interaction studies. Immobilization of the GAGs hyaluronic acid and chondroitin sulfate was achieved using different methods. Immobilization was followed in real-time using quartz crystal microbalance with dissipation monitoring and surface plasmon resonance. Several GAG-interacting proteins were studied: e.g. bone morphogenetic protein-2, aggrecan, and virus glycoproteins.
Studying the interactions revealed interesting aspects of the interaction in itself, as well as highlighted important aspects regarding the surface immobilization of the GAGs. The interactions are highly dependent on the surface orientation of the GAGs and pros and cons with side-on versus end-on immobilization of GAGs are discussed in the thesis. The immobilizing technique, especially if functional groups are introduced on the GAG, also influences how the GAG is perceived by a secondary protein.
Potential applications of the GAG platforms are described; studying initial attachment of chondrocytes towards better cartilage implants and aggregation of platelets at a surface interface.