The intrinsically disordered N-terminus of the Antenna Protein CP29 from plant photosynthesis

Maryam Hashemi Shabestaria, Cor J.A.M. Wolfsb, Ruud B. Spruijtb, Herbert van Amerongenb, Martina Hubera
aDepartment of Molecular Physics, Leiden University, P.O. Box 9504, 2300 RA Leiden, the Netherlands; bLaboratory of Biophysics, Wageningen University, P.O. Box 8128, 6700 ET Wageningen, the Netherlands

The N-terminus of the plant antenna protein CP29 consists of 100 aminoacid residues that could not be resolved in the crystal structure. [1] The function of this part of the protein is unknown, and for flexibleproteins, standard methods of analysis do
not work. Here we show an approach based on electron paramagnetic resonance (EPR) to find out if this long stretch of protein has structure and if so, what we can find out about its conformation.

We combine mobility information from spin-label, continuous wave EPR from 55 of the 100 amino-acid residues of the N-terminus with distance measurements by pulsed Electron-Electron-Double resonance (DEER). We find that sections of the Nterminus
are immobilized, showing that this flexible part of the protein must possess some structure. Distance measurements within the tail reveal a small number of defined conformations, emphasizing the idea that the tail has a function. [2]

Earlier, disordered sections of proteins and intrinsically disordered proteins (IDP’s) became known in the context of neurodegenerative diseases, and we have shown different EPR approaches to disease-related IDP’s from Alzheimer’s or Parkinson’s disease [3]. Here we apply them to a possibly functional protein section.

Figure: Left: Side view of CP29 (ordered section red) in the photosynthetic membrane (yellow) with cartoon rendering of possible structures of N-terminus (green). Right: Top view of membrane, with CP29 (red ellipsoid). The N-terminus (blue), may interact with other membrane-antenna proteins (light green and grey) to form complexes suitable to light conditions. Phosphorylation sites (red circles) in the tail region may be involved in regulation.

References

[1] Pan et al., Nat.Struct.Mol.Biol. 2011, 18, 309-315
[2] M. Hashemi Shabestari, C.J.A.M. Wolfs, R.B. Spruijt, H. van Amerongen, M. Huber Biophysical Journal 2014 106 1349-1358.
[3] Pravin Kumar, Ine M.J.Segers-Nolten, Nathalie Schilderink,Vinod Subramaniam, Martina Huber PLOS One 2015 DOI: 10.1371/journal.pone.0142795 and references therein