Analysis of Phosphoinositide-Binding Properties and Subcellular Localization of GFP-Fusion Proteins
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Specific protein-phosphoinositide (PI) interactions are known to play a key role in the targeting of proteins to specific cellular membranes. Investigation of these interactions would be greatly facilitated if GFP-fusion proteins expressed in mammalian cells and used for their subcellular localization could also be employed for in vitro lipid binding. In this study, we found that lysates of cells overexpressing GFP-fusion proteins could be used for in vitro protein-PI binding assays. We applied this approach to examine the PI-binding properties of Aplysia Sec7 protein (ApSec7) and its isoform ApSec7(VPKIS), in which a VPKIS sequence is inserted into the PH domain of ApSec7. EGFP-ApSec7 but not EGFP-ApSec7(VPKIS) did specifically bind to PI(3,4,5)P3 in an in vitro lipid-coated bead assay. Overexpression of EGFP-ApSec7 but not EGFP-ApSec7(VPKIS) did induce neurite outgrowth in Aplysia sensory neurons. Structure modeling analysis revealed that the inserted VPKIS caused misfolding around the PI(3,4,5)P3-binding pocket of ApSec7 and disturbed the binding of PI(3,4,5)P3 to the pleckstrin homology (PH) domain. Our data indicate that plasma membrane localization of EGFP-ApSec7 via the interaction between its PH domain and PI(3,4,5)P3 might play a key role in neurite outgrowth in Aplysia.
KeywordsGFP-fusion protein Phosphoinositide PI(3,4,5)P3 Aplysia Sec7 In vitro protein-phosphoinositide binding Neurite outgrowth
Aplysia Sec7 protein
PI4P adaptor protein ½
Ceramide transfer protein
GDP/GTP exchange factor
ADP ribosylation factor
ARF binding site opener
Rapamycin-binding domain of mTOR
FK506 binding protein 12
Polyphosphate 5-phosphatase E
This work was supported by Basic Science Research Program through NRF (2014-R1A1A2012804) funded by the Ministry of Education (D.-J. J), Science and Technology, and by the National Honor Scientist Program of Korea (D.-J. J & B.-K. K). S.K and I.C are supported by the MIREBraiN program of DGIST and the National Creative Research Initiatives (Center for Proteome Biophysics) of National Research Foundation, Korea (No. 2008-0061984).
Conflict of interest
There is no conflict of interest.
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