Backbone assignment and secondary structure of the PsbQ protein from Photosystem II
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PsbQ is one of the extrinsic proteins situated on the lumenal surface of photosystem II (PSII) in the higher plants and green algae. Its three-dimensional structure was determined by X-ray crystallography with exception of the residues 14–33. To obtain further details about its structure and potentially its dynamics, we approached the problem by NMR. In this paper we report 1H, 15N, and 13C NMR assignments for the PsbQ protein. The very challenging oligo-proline stretches could be assigned using 13C-detected NMR experiments that enabled the assignments of twelve out of the thirteen proline residues of PsbQ. The identification of PsbQ secondary structure elements on the basis of our NMR data was accomplished with the programs TALOS+, web server CS23D and CS-Rosetta. To obtain additional secondary structure information, three-bond HN-Hα J-coupling constants and deviation of experimental 13Cα and 13Cβ chemical shifts from random coil values were determined. The resulting “consensus” secondary structure of PsbQ compares very well with the resolved regions of the published X-ray crystallographic structure and gives a first estimate of the structure of the “missing link” (i.e. residues 14–33), which will serve as the basis for the further investigation of the structure, dynamics and interactions.
KeywordsPhotosystem II PsbQ Missing link NMR resonance assignment Protein–protein interaction
We would like to thank J.B. Arellano from CSIC Salamanca for providing the JR2592 expression vector, P. Schmieder, M. Beerbaum and B. Schlegel from FMP-Berlin for obtaining high field NMR spectra and for the helpful discussions. R. Keller is gratefully acknowledged for the assistance with CARA. For the use of web portals, computing and storage facilities the eNMR project (European FP7 e-Infrastructure grant, contract no. 213010, www.enmr.eu), supported by the national GRID Initiatives of Italy, Germany and the Dutch BiG Grid project (Netherlands Organization for Scientific Research) is acknowledged. This work has been supported by the Austrian Academic Exchange Service ÖAD (WTZ-AT-CZ), the Austrian Science Fund FWF (P18384 to W.S. and P15380 to N.M.) and East NMR Program of the European Union (EU FP7 Project/Contract number 228461). R. Ettrich and J. Kohoutova gratefully acknowledge support from the Ministry of Education, Youth and Sports of the Czech Republic (MSM6007665808, LC06010) and the Academy of Sciences of the Czech Republic (AVOZ60870520).