Sushant Suresh

Topic

Molecular mechanisms involved in the regulation of phosphatidylinositol 4-kinase III α (PI4KIIIα/PI4KA)

Department of Biochemistry and Microbiology

Date & location

• Friday, October 17, 2025
• 11:00 A.M.
• Engineering & Computer Science Building, Room 128

Examining Committee

Supervisory Committee

• Dr. John Burke, Department of Biochemistry and Microbiology, University of Victoria (Supervisor)
• Dr. David Goodlett, Department of Biochemistry and Microbiology, UVic (Member)
• Dr. Lisa Reynolds, Department of Biochemistry and Microbiology, UVic (Member)
• Dr. Scott McIndoe, Department of Chemistry, UVic (Outside Member)

External Examiner

• Dr. Miklos Guttman, Department of Medicinal Chemistry, University of Washington

Chair of Oral Examination

• Prof. Asad Kiyani, Faculty of Law, UVic

Abstract

One of the first steps in the phosphoinositide signalling pathway is the generation of phosphatidylinositol 4-phosphate (PI4P) from phosphatidylinositol (PI). Once considered just an intermediate for phospholipase C (PLC) signalling, PI4P has now emerged as a critical player in membrane trafficking and lipid transport. The predominant pool of PI4P at the plasma membrane is generated by the type III phosphatidylinositol 4-kinase alpha (PI4IIIa/PI4KA). In the cell, PI4KA exists as a large, 750 kDa dimer of heterotrimers along with two accessory proteins, TTC7 and FAM126. Critical to the regulation of PI4KA is its interaction with protein and lipid binding partners. Dysregulation of this pathway leads to severe neurological, gastrointestinal and immunological disorders. Additionally, PI4KA can be hijacked by the hepatitis C virus to promote viral replication and disease. Due to the severe toxicity attributed to existing therapeutics, a deeper understanding of the molecular mechanisms underlying PI4KA regulation is required.

In this dissertation, I employed a combination of advanced scientific techniques, including protein biochemistry, bio-layer interferometry (BLI), hydrogen deuterium exchange mass spectrometry (HDX-MS), and cryo-electron microscopy (cryo-EM), to elucidate the molecular basis for the regulation of PI4KA by binding partners, calcineurin and EFR3. This multifaceted approach advances our understanding of how this enzyme is recruited to the membrane, activated at the membrane and regulated at the membrane to better develop targeted therapeutics in disease. This dissertation will consist of an introduction chapter introducing PI4KA signalling, the various players involved in its regulation and its role in disease. It will be followed by two data chapters that expand our knowledge on the regulatory mechanisms by which the enzyme is regulated by proteins, calcineurin and EFR3. The third data chapter aims to put forth the idea of a biochemical tool that may be used to selectively target PI4KA activity in disease. Finally, the last chapter will summarize the research and present future directions in the field.

Collectively, the work presented here provides unique insight into how PI4KA is recruited to the membrane, the role of phosphorylation in its regulation and how these regulatory mechanisms can be specifically targeted in disease.