Src kinase is a key element in many signaling pathways affecting cellular processes such as differentiation, proliferation, motility, or migration. Deregulation of its activity is associated with the promotion of cancer. Therefore, understanding its cellular function is vital. Src activity directly correlates with its structure; when Src is active, it adopts opened conformation, when inactive, it is in closed conformation stabilized by intramolecular interactions. Detection of the conformation can be used to analyze Src activity. In this thesis, conformation-sensitive FRET-based Src biosensor was improved using mNeonGreen as a new acceptor fluorophore in the existing design and the properties of the new biosensor were compared with the original Src biosensor. The new biosensor is able to detect changes in Src conformation and can be stably expressed in cells. Src activity in focal adhesion was analyzed and higher Src activity in these structures was confirmed. Although the new biosensor did not exhibit significantly better sensitivity to Src conformational changes, it still proved to be a useful tool to study Src activity, and mNeonGreens higher brightness makes it more suitable for microscopic experiments. Key words: Src, FRET, biosensor, live-cell imaging, mNeonGreen

Alzheimer’s Disease, also called AD, is a horrible, degenerative brain disease that more than 35 million people over the world have. Today, there is no cure for this disease, only treatments that are temporarily relieving the symptoms. The two proteins that is thought to be the main cause of AD is amyloid β (Aβ) and tau. Previously, people have tried studying Aβ in vivo using green fluorescent protein fusion together with Aβ. However, this is difficult since the aggregation of Aβ will lead to loss of fluorescence. This study aimed to crystallize the fusion protein mNG-A β1-42 and to investigate its properties as a molecular fluorescent Aβ-amyloid specific probe. Dynamic light scattering (DLS) was used to confirm that the majority of the protein was not in the form of soluble aggregates. The DLS experiments were followed by several rounds of crystallization trials. Initial screening and the subsequent narrowing down of potential conditions where mNG-Aβ1-42 could form crystals. Several staining experiments were conducted as well, including staining brain tissue from mouse with both Swedish and Arctic mutation, from human patients with sporadic AD and from human patients with AD with the Arctic mutation. The DLS experiments showed that the protein used in the crystallization experiments mostly consisted of molecular particles of the same radius. However, there was clear evidence of some larger species present that could have been a potential problem for crystallization. Crystallization experiments suggested that PEG 8000 was the most promising precipitant amongst other conditions identified for crystallization of mNG-Aβ1-42. However, the study was ultimately unsuccessful in developing crystals of sufficient high quality for diffraction studies to commence. The staining experiments demonstrated that mNG-Aβ1-42 could bind both by itself and with another amyloid probe, Congo red, and with antibodies in brain tissue from mouse with both Swedish and Arctic mutation, from human patients with sporadic AD and from human patients with AD with the Arctic mutation. In conclusion, several characteristics of mNG-Aβ1-42 were revealed in this study.