Conformational changes of PsbQ protein from PSII studied by NMR
Abstrakt
PsbQ is an extrinsic protein of photosystem II (PS II) playing a role in calcium and
sodium homeostasis for oxygen evolving complex in photosynthesis. The solution structure
of PsbQ in phosphate buffer including a short N-terminal helix has been resolved recently.
The incorporation of PsbQ in PS II and its interactions with other PS II proteins were not
elucidated yet. As a prerequisite for detailed interaction studies with other extrinsic PS II
proteins such as PsbP, suitable conditions for nuclear magnetic resonance (NMR)
investigations of both interacting partners should be established.
In this thesis the stability of PsbQ in different buffers, as well as the influence of pH,
temperature and salt concentration was investigated. Following stability tests, candidate
buffer conditions were chosen for further NMR experiments exploring the influence on
protein conformation and dynamics.
Previously it had been found that Bis-Tris buffer provides suitable conditions for PsbP,
while PsbQ had been investigated in phosphate buffer. In this work I established, that Bis-
Tris buffer is appropriate for PsbQ as well, but that it may undergo structural and dynamical
changes as evidenced by NMR experiments on recombinant stable isotope (N-15) labeled
protein preparations.
Some newly observed nuclear Overhauser effect (NOE) correlation indicate possible
interactions from the N-terminal stretch to a loop region between the four stable helices of
PsbQ. This indicates a less flexible solution structure than the one found in phosphate
buffer, which still deviates significantly from the earlier crystal structure. Further studies are
required to refine a three-dimensional structure based on these NOEs and some
characteristic chemical shift changes.