Maria Tsemperouli, Ph.D.

Postdoctoral Associate

Ph.D., University of Geneva in Switzerland (2018)

My project aims to reveal the molecular mechanisms that govern neurotransmitter release using a combination of biochemical reconstitution, electrophysiological and biophysical methods. Neurotransmitter release involves calcium-triggered fusion of cargo-loaded vesicles to the plasma membrane. The initial connection between the fusing membranes, called the fusion pore, can evolve in various ways, including rapid dilation to allow full cargo release, slow expansion, repeated opening-closing, and resealing. The dynamics of the fusion pore determine cargo release rates and mode of vesicle recycling. A tripartite complex formed between SNARE proteins, Synaptotagmin-1, and Complexin-1 has been proposed to constitute the minimal machinery for fast (1-5 ms), synchronous neurotransmitter release, but previous reconstitutions of calcium-triggered release had time resolutions of 0.4-100 s, ≳ 100-fold slower than needed for studying kinetics of synchronous release. In most neurons, release rates depend steeply on [Ca2+], but because multiple Ca2+ sensors are present and copy numbers are not controlled, what determines this high cooperativity and the factors which regulate pore dynamics are not understood. A major bottleneck in advancing our understanding of these phenomena has been a lack of in vitro assays with sensitivity and sufficient time resolution to resolve the dynamics of single fusion pores. The Karatekin lab has developed such methods over the past few years and used them to probe properties of fusion pores induced by SNAREs alone, or with Synaptotagmin-1. In my project, I aim to enhance those approaches such that [Ca2+] can be elevated rapidly (≲1 ms) to trigger fusion. This will allow addressing the following fundamental questions: 1) What is the minimal machinery for rapid Ca2+- triggered fusion? 2) What determines the Ca 2+-cooperativity of release.

Before I join the Karatekin Lab, I received my PhD in physical chemistry and membrane biophysics from the Université de Genève in Switzerland. My research aimed on a platform development based on artificial free-standing lipid bilayers which can be imaged and polarized at the same time for the characterization of active membrane components. Through this multidisciplinary project, I obtained strong experience in in vitro electrophysiology and rich knowledge about the biophysics of lipid membranes. The position was funded by the National Centre of Competence in Research (NCCR) Chemical Biology and the National Swiss National Science Foundation (SNSF).

I graduated from University of Crete, Heraklion in Greece, where I obtained my BSc degree from the Chemistry Department with a solid knowledge in general chemistry. At the same Department, I later received my MSc degree in analytical chemistry and electrochemistry