Structures of photoactive proteins studied by (in-situ) neutron scattering

Prof. Dr. Jörg Pieper

1) The solution structure of Photosystem I (PSI) was determined for the first time using small angle scattering (SANS) and selectively deuterated (“invisible”) detergents.

2) The solution structures of the orange carotenoid protein under illumination and of its complex with the fluorescence recovery protein were determined for the first time using small angle scattering (SANS) and selectively deuteration.

The group at the Institute of Physics, Tartu, Estonia, prepared and performed neutron scattering experiments (small angle scattering) and constructed a setup for in- situ optical excitation of the samples. Finally, data analysis and the development of structural models were carried out here.

The group at the Humboldt Universität zu Berlin, Germany, prepared and supplied complexes of PSI with different electron donors and acceptors for biotechnological applications. PSI was isolated using fully deuterated (“invisible”) detergents for SANS with contrast variation, because matching of protonated detergent is inherently incomplete and may result in artifacts in structural models derived from SANS data.

The group at Technische Universität Berlin, Germany, prepared samples of the orange carotenoid protein with different carotenoid content and complexes with fluorescence recovery protein using partial deuteration for SANS with contrast variation.

The experiments were carried out at ILL Grenoble, France, using small angle neutron scattering, in part with in-situ illumination, within the user service of the neutron scattering facility. The experiments planned at MLZ Garching, Germany, could not be performed because of technical difficulties at this facility.

Direct: The project strengthened the collaboration between the neutron scattering group at the Institute of Physics in Tartu, Estonia, and the groups at HU Berlin and TU Berlin. In total, one postdoc and four PhD students were involved in the project at Institute of Physics (Maksym Golub, Nicholas Croy, Mina Hajizadeh), HU Berlin (Jelena Boyka), and TU Berlin (Marcus Moldenhauer).

Indirect: Within Estonia and other Baltic states, a community of about 20-30 scientists in neutron scattering will benefit from dissemination of the expected results. In addition, the methods developed will contribute to Estonian contributions for the European Spallation Source. Here, the community of benefitting scientists may be up to several thousands.