Presenter: Amanda J. Davis
Advisor(s): Wendy F. Boss
Author(s): Amanda J. Davis, Yang Ju Im and Wendy F. Boss
Graduate Program: Botany

Title: Arabidopsis PIPK1 Is Involved In A Scaffold With F-actin And Recruits PI4Kbeta1 To The Cytoskeleton

Abstract: Phosphatidylinositol phosphate 5-kinases (PtdInsP 5-kinases) are a family of enzymes that phosphorylate phosphatidylinositol-4-phosphate (PtdIns4P) to form phosphatidylinositol-4,5-bisphosphate (PtdIns(4,5)P2). These enzymes are found in all eukaryotic systems, and in many systems may be the flux limiting step in the phosphoinositide pathway. Arabidopsis has 11 PtdInsP 5-kinases, 9 of which contain the Membrane Occupation and Recognition Nexus (MORN) domain. The MORN domain is not found in any other lipid kinases and its function is unknown although, when removed the activity of the PtdInsP 5-kinase increases 3-fold. The relatively low ratio of PtdIns(4,5)P2:PtdIns4P in plants can be explained in part by the biochemical properties of the plant PtdInsP 5-kinases. The plant PtdInsP kinases have up to 3-fold higher Km for PtdIns4P and up to 60-fold lower Vmax as compared to HsPIPK1alpha. Our goal was to investigate the protein-protein interactions of a representative of this family of enzymes, AtPIPK1, and investigate the role of the MORN domain in those interactions. AtPIPK1, was found to interact selectively with proteins involved in phospholipid biosynthesis and in regulating the actin cytoskeleton. Actin polymerization studies indicated that AtPIPK1 could be recovered in an F-actin fraction. PI4Kbeta1, which synthesizes PtdIns4P, was found with the F-actin fraction only when PIPK1 was present indicating that PIPK1 can recruit PI4Kbeta1 to the cytoskeleton. The MORN domain was neither necessary nor sufficient for interaction with actin or PI4Kbeta1. These results indicate that the MORN domain could be involved in processes other than mediating protein-protein interactions and demonstrate a link between the inositol lipids, the protein translational machinery and the cytoskeleton.