Functional characterization of the inverse FBAR-containing proteins srGAP1 and Carom

Abstract

The Slit-Robo GTPase activating protein family (srGAPs) consists of four members and are important multi-domain adaptor proteins, which are involved in axonal pathfinding and various other neuronal processes. This thesis explores the function of the human srGAP1 protein as well as its zebrafish homolog in three ways: 1) examining of the membrane deforming activity of the FBAR domain, 2) analysing the specific activity of the srGAP1 GAP domain towards three members of RhoGTPases, and 3) identifying potential novel interaction partners for the srGAP1 protein with the intention to determine new pathway involvements for the protein. The work presented in this thesis shows that the srGAP1 FBAR domain can induce vesicle deformation in vesicle-based in vitro assays. Compared to the results of another FBAR domain-containing protein, the Carom protein, the srGAP1 FBAR domain is less potent in inducing invaginations of giant unilamellar vesicles. Both proteins do not induce formation of tubules as seen for classical FBAR domains, but lead to invaginations of the vesicles. Based on these results both proteins can be assigned to the recently found inverse FBAR subfamily. This work also measures the intrinsic GTP hydrolysis accelerating activity of the srGAP1 GAP domain with different NMR approaches. A comparison of the srGAP1 GAP domains of human and zebrafish showed species-specific interaction with Cdc42. Cross-interactions between the GAP domains and Cdc42 from different organism, namely human and zebrafish, was observed to a low extent. Finally, this work identifies possible new interaction partners for the srGAP1 protein with mass spectrometry analysis, which indicate that the srGAP1 protein might have a more complex and diverse role than assumed so far.