Anderson, Deborah H.2013-02-262013-02-262012-012013-02-25January 20http://hdl.handle.net/10388/ETD-2012-01-315The adaptor subunit of phosphatidylinositol 3'-kinases (PI3K), p85, is involved in many different biological processes. Recent studies have shown that one of these functions is to serve as a GTPase activating protein (GAP) towards Rab5, a small monomeric G-protein. Rab5, like other G-proteins, can bind to either GDP or GTP in vivo, assuming its inactive and active form, respectively. The p85 protein has been shown to associate with both the nucleotide-bound and nucleotide-free states of Rab5. It has also been shown that p85 associates with activated, phosphorylated platelet-derived growth factor receptors (PDGFRs) via its two SH2 domains, and that upon binding there is a conformational change in the p85 protein which leads to a derepression of p110 kinase activity. The purpose of this study was to analyze if binding of the activated PDGFR peptides to p85 affects its Rab5GAP activity, as well as to measure the binding affinity of p85 towards Rab5 in each of its nucleotide-bound states. GAP assays were performed to measure the effect that peptide analogs of both the activated and inactivated PDGFR had on p85 Rab5GAP activity, while the binding affinity of p85 towards Rab5 was measured using surface plasmon resonance. The results of this study suggest that PDGFR peptides have no significant effect on p85 Rab5GAP activity. Furthermore, p85 appears to have a higher magnitude of binding to nucleotide-associated Rab5 proteins, than nucleotide-free Rab5 proteins. It also appears that p85 forms more stable complexes with Rab5-GTP than with Rab5-GDP. These results further support previous studies that show p85 to be an important regulator of Rab5-mediated endosomal fusion and show that this activity is not regulated by binding to the activated PDGFR itself.engPI3KRab5Endocytosisp85PDGFRSignallingPeptideGTPase Activating Proteintext