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Chlorophyll a/b binding-specificity in water-soluble chlorophyll protein


We altered the chlorophyll (Chl) binding sites in various versions of water-soluble chlorophyll protein (WSCP) by amino acid exchanges to alter their preferences for either Chl a or Chl b. WSCP is ideally suited for this mutational analysis since it forms a tetrameric complex with only four identical Chl binding sites. A loop of 4–6 amino acids is responsible for Chl a versus Chl b selectivity. We show that a single amino acid exchange within this loop changes the relative Chl a/b affinities by a factor of 40. We obtained crystal structures of this WSCP variant binding either Chl a or Chl b. The Chl binding sites in these structures were compared with those in the major light-harvesting complex (LHCII) of the photosynthetic apparatus in plants to search for similar structural features involved in Chl a/b binding specificity.

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Data availability

The authors declare that the data supporting the findings of this study are available from the corresponding authors upon request. Crystal structures determined in this study have been deposited in the Protein Data Bank (, with accession code 6GIW (LvPCPS Chl a) and 6GIX (LvPCPS Chl b).

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We thank T. Hares for WSCP mutant preparation and S. Müller for preliminary experiments. Moreover, we thank E. Hofmann for providing definition files for Chl ligands and helpful discussion. We are grateful to D. Noy for valuable discussion. This work has been funded by a grant from the Deutsche Forschungsgemeinschaft to H.P. (Pa 324/10-1). P.G. thanks the Studienstiftung des deutschen Volkes for support.

Author information

H.P. designed the research. S.T. and H.S. designed the WSCP mutants. P.G. developed the reconstitution method. D.M.P., A.A. and V.A. prepared the WSCP samples and performed and analysed the spectroscopic measurements. E.J. resolved the crystal structures. A.A. analysed the crystal structures. D.M.P., A.A., M.W. and H.P. wrote the paper.

Competing interests

The authors declare no competing interests.

Correspondence to Elmar Jaenicke or Harald Paulsen.

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Fig. 1: Comparison of investigated Chl a/b binding proteins.
Fig. 2: Chl a/b affinity motifs in WSCP.
Fig. 3: Qualitative determination of relative Chl a/b binding affinities.
Fig. 4: Quantitative determination of relative Chl a/b binding affinities.
Fig. 5: Comparison of the aligned crystallographic structures of Lv-wt (grey)27 and LvPCPS (with Chl a in blue, PDB-code: 6GIW; with Chl b in green, PDB-code: 6GIX).
Fig. 6: Interaction between the different Chl-selectivity motifs with bound Chl b.
Fig. 7: Surrounding of the C-71 groups of LHCII-bound Chls b molecules.
Fig. 8: Surrounding of the C-71 group of LHCII-bound Chls a.