Doctoral defence: Mina Hajizadeh Omaslanolya „Structure and dynamics of photoactive proteins studied by (in situ-) neutron scattering methods“

On 26 August 2025 at 14.15, Mina Hajizadeh Omaslanolya will defend her doctoral thesis „Structure and dynamics of photoactive proteins studied by (in situ-) neutron scattering methods“ („Fotoaktiivsete proteiinide struktuuri ja dünaamika uurimine (in situ) neutronhajumise meetoditega“).

Supervisors:
professor Jörg Pieper, University of Tartu
researcher Maksym Golub, University of Tartu

Oponent:
Dr. Viktor Petrenko, Neutron Science, Basque Foundation for Science, Bilbao, Spain

Summary
This doctoral thesis investigates the structure and dynamics of photoactive proteins using state-of-the-art neutron and X-ray scattering techniques. The primary focus is on the Orange Carotenoid Protein (OCP), a key photoprotective component in cyanobacteria, and the Water-Soluble Chlorophyll-binding Protein (WSCP), a simplified model for studying pigment–protein interactions. These systems serve as models for understanding how light-induced conformational changes and protein flexibility regulate biological function, particularly in light-harvesting and energy dissipation processes.

A combination of complementary experimental methods, including Small-Angle Neutron Scattering (SANS), Quasielastic and Inelastic Neutron Scattering (QENS and INS), and Time-Resolved Small-Angle X-ray Scattering (TR-SAXS), is used to characterize both static structures and dynamic transitions in protein systems under near-physiological conditions. In paper I, SEC-SANS is employed to resolve the solution structures and oligomeric states of OCP–FRP complexes, providing insights into their role in the photoactivation and thermal relaxation cycles of OCP. In paper II, QENS is used to assess the internal mobility of various OCP variants and in Paper III INS with QENS has been used to study WSCP systems, revealing how pigment content, solvent environment, and temperature influence protein flexibility and function. TR-SAXS captures the real-time conformational dynamics of the OCP during deactivation from its light-activated red form (OCPR) back to its resting orange form (OCPᴼ).

The findings of this work offer a comprehensive picture of how protein structural plasticity and dynamic behavior underlie the functional switching mechanisms in photoactive proteins. Beyond advancing the fundamental understanding of protein photophysics and photoprotection in cyanobacteria, the results also inform the design of artificial light-harvesting systems, synthetic photoprotective materials, and optogenetic tools. By bridging studies of complex biological systems with minimal model proteins, this thesis contributes to the broader field of structural biology, shedding light on the interplay between structure, dynamics, and function in biological macromolecules.