Immunoassayer är en väldigt vanlig metod för koncentrationsbestämning av biomolekyler. Denna metod nyttjar antikroppars affinitet för vissa analyter. I detta projekt har det undersökts om Gyros AB:s detektionsinstrument kan göras känsligare. Flera förslag har tagits fram genom efterforskning i artiklar och intervjuer med personer insatta inom området. De metoder som projektgruppen valt att presentera för företaget är enzymbaserad immunoassay med fluorescerande substrat samt multipel inmärkning av antikroppar, vilket vi tror kommer bidra till att försärka den fluorescerande signalen. Immobilisering av antikroppar med hjälp av traptavidin är ytterligare ett framtaget förbättringsförslag som syftar till att bidra med starkare och förlängd immobilisering av antikroppar till den fasta fasen i immunoassay. Flertalet andra metoder har undersökts såsom detektion med hjälp av radioaktivitet och kemiluminiscens. Inga fortsatta studier gjordes på grund av svårigheter att anpassa metoderna till de nuvarande instrumenten. Vi tror att de förslag på metodförbättringar som vi föreslår kan förbättra känsligheten på Gyros mätningar om de implementeras på den nuvarande plattformen.

The Streptomyces avidinii protein streptavidin binds the small molecule biotin (vitamin H / B₇) with extraordinary stability, resulting in the streptavidin-biotin interaction being one of the strongest non-covalent interactions known in nature (K_d ~ 10^-14 M). The stable and rapid biotin-binding, together with high resistance to heat, pH and proteolysis, has given streptavidin huge utility, both in vivo and in vitro. Accordingly, streptavidin has become a widely used tool in many different biotechnological applications. Streptavidin has also been the subject of extensive research efforts to glean insights into this paradigm for a high-affinity interaction, with over 200 mutants of the protein reported to date. Despite the high stability of the streptavidin-biotin interaction, it can and does fail under certain experimental conditions. For example, streptavidin-biotin dissociation is accelerated by an increased temperature or lower pH (conditions often encountered in cellular imaging experiments), and by mechanical stress, such as the shear force arising from fluid flow (encountered when streptavidin is used as a molecular anchor in biosensor chips and arrays). This study details efforts made at increasing further the utility of streptavidin, by increasing the stability of biotin and biotin-conjugate binding. A rational site-directed mutagenesis approach was used to create 27 mutants, with eight of these mutants possessing higher-stability biotin-binding. The most stable biotin-binding mutant was named traptavidin and was extensively characterised. Kinetic characterisation revealed traptavidin had a decreased dissociation rate from biotin and biotin-conjugates when compared to wildtype streptavidin, at both neutral pH and pH 5. Atomic force microscopy and molecular motor displacement assays revealed the traptavidin-biotin interaction possessed higher mechanical stability than the streptavidin-biotin interaction. Cellular imaging experiments revealed the non-specific cell binding properties of streptavidin were unchanged in traptavidin. X-ray crystallography was also used to generate structures of both apo- and biotinbound traptavidin at 1.5 Å resolution. The structures were analysed in detail and compared to the published structures of streptavidin, revealing the characteristics of traptavidin arose from the mutations stabilising a flexible loop over the biotin-binding pocket, as well as reducing the conformational change on biotin-binding to traptavidin. Traptavidin has the potential to replace streptavidin in many of its diverse applications, as well as providing an insight into the nature of ultra-stable noncovalent interactions.