Identification and understanding of the protein-protein interaction and the modifications of proteins are essential for understanding almost all the biological events from development to death of an organism. Mass spectrometry has been extensively used to address the fundamental questions related to protein modifications and interactions because it enables precise determination of molecular masses of peptides and proteins with high sensitivity, and therefore unambiguous identification and sequencing of proteins. Here, we develop crucial mass spectrometry techniques for more sensitive and effective protein analysis. We also explore various types of optical imaging techniques, which can provide complementary information about proteins’ function in their physiological conditions.

We integrate chemical crosslinking techniques with mass spectrometry, which allows for the detection of transient non-covalent interactions between proteins through the formation of stable chemical bonds between them. Crosslinking patterns combined with x-ray crystallographic structural data can be used to identify the binding domains for a protein complex. We also introduce a new ambient mass spectrometry named Laser Desorption/Ionization Droplet Delivery (LDIDD) mass spectrometry (MS). It utilizes a pulsed laser for desorption/ionization within a liquid droplet in contact with the surface containing molecules to be mass spectrometrically analyzed while liquid droplet serves as the ion carrier and delivers the desorbed and ionized species to the inlet of a mass spectrometer. There mass spectrometric methods are used for studying protein-protein interactions and modifications.

Figure . Mass spectrometric analysis for the interaction between photosynthetic complexes. (A) Schematic representation of reorganization of photosynthetic complexes of light harvesting complex (LHC) and photosystem (PS) under different light conditions. (B) Mass spectrometric measurement and imaging of post-translational modifications of proteins and protein-protein interactions with Laser or desorption electrospray ionization (DESI) mass spectrometry (C) Cross-linking mass spectrometry for the studying transient protein interactions.

At its core, photosynthesis is a chemical process converting light energy into chemical energy through a number of complex processes including photon absorption, electronic energy transfer, water splitting, etc. The very early process of photon abortion is assisted by the antenna proteins called light harvesting complexes (LHCs) surrounding the reaction center photosystems (PSs), where the actual water splitting occurs. The LHC and PS form a highly ordered structure that is strongly coupled to its function, i.e. efficient absorption of photons and energy transfer. Upon the environmental changes such as low or high level of light illumination, photosynthetic complexes undergo organizational/distributional changes to achieve maximum utilization of available light energy and/or protection of the photosynthetic complexes (Fig). Here, we employ the aforementioned mass spectrometric tools for protein analysis for studying this early photosynthetic process, especially focusing on the interactions between protein complexes of LHC and PS under different light conditions. The crosslinking of the LHCs and PSs will be conducted to capture transient weak interactions between them (Fig. C). The binding between LHC and PS will also be studied in their intact states with Desorption Electrospray Ionization (DESI) and Laser Desorption/Ionization Droplet Delivery (LDIDD) mass spectrometry (MS) for more effective and high-throughput analysis of the interactions and spatial organization of the protein complexes in plant leaf samples under localized light stress conditions (Fig. B).

  1. Mass spectrometric analysis for protein-protein interaction of photosynthetic complexes
a. The capture of transient intermediate states by means of chemical cross-linking
b. High resolution mass spectrometry imaging for single cell analysis and distribution of small molecules in plant and
animal tissue for the studies of cellular heterogeneity
c. Analysis of cellular signaling during state transition in photosynthesis
2. Understand the mechanism of energy transfer in photosynthesis
a. Energy transfer efficiency and adaptation upon change in light conditions during state transition in photosynthesis
b. Systems biological modeling and understanding of state transition in photosynthesis

Member for these studies
Lee, Sangmoon
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