Incorporating glucose oxidase activity into amyloid fibrils
Degree GrantorUniversity of Canterbury
Degree NameMaster of Science
Amyloid fibrils are a misfolded state formed by many proteins when subjected to denaturing conditions. Their constituent amino acids make them an excellent target for enzyme immobilisation and their strength, stability and nanometre size are attractive features for exploitation in the creation of new bionanomaterials. The aim of this thesis was to functionalise amyloid fibrils by conjugation to glucose oxidase (GOD). GOD is a relatively stable glycoprotein that catalyses the oxidation of glucose and the release of hydrogen peroxide. The consumption of glucose can be measured to assess glucose levels, and the release of hydrogen peroxide is cytotoxic to cells and is thus an effective antibacterial agent. Three methods of attachment were used: cross-linking using glutaraldehyde, periodate oxidation of the glycoprotein shell, and cross-linking using glutaraldehyde following deglycosylation. GOD retained activity upon attachment by all three methods. These attachment methods were assessed using electrophoresis, centrifugation, sucrose gradient centrifugation and TEM. Gel electrophoresis indicated a high degree of cross-linking and TEM showed no significant change of fibril morphology upon cross-linking. Centrifugation experiments suggested a non-covalent interaction was occurring between amyloid fibrils and GOD, and a covalent attachment was occurring upon addition of glutaraldehyde. Sucrose gradient centrifugation provided increased separation of cross-linked material compared to other separation methods, and showed greater cross-linking to crystallin amyloid fibrils than insulin fibrils. Cross-linking native GOD using glutaraldehyde was chosen for further experiments, as it was found to be most effective for GOD attachment to amyloid fibrils. The resulting functionalised enzyme scaffold was then incorporated into a model poly(vinyl alcohol) (PVOH) film, to create a new bionanomaterial. The distribution of the functionalised fibrils through the film was characterised using SEM and confocal microscopy, where film components were found to be unevenly dispersed. The antibacterial effect of the functionalised film was then tested on E. coli and the antifungal effect of the film was tested on Fusarium, Rhizopus and Penicillium. Growth of E. coli was inhibited around functionalised film circles, demonstrating the incorporation of GOD antibacterial activity into the PVOH film. However, no growth inhibition of fungal species was observed. This work is of significance as it demonstrates the ability to convert a waste material, bovine lens crystallin, to high value protein nanofibres and incorporate functionality via GOD attachment. The incorporation of the GOD-functionalised amyloid fibrils into PVOH provides an excellent ‘proof of concept’ model for the creation of a new bionanomaterial using a functionalised amyloid fibril scaffold. Future development of this model system has the potential to lead to the production of a novel biomaterial for use in food packaging due to the antimicrobial properties of GOD.