Water-soluble Chlorophyll Protein (WSCP)
Whereas all chlorophyll proteins of the photosynthetic apparatus in plants are membrane proteins, this is not true for the water-soluble chlorophyll protein WSCP, which is present in Brassicaceae and some other families. The crystal structure of two WSCPs has been solved but the biological function of the protein is still unclear. WSCP expression has been shown in several cases to be induced by stress or senescence. The protein exhibits only marginal sequence homology with other chlorophyll-binding proteins but contains the signature sequence of Kunitz trypsin inhibitors. An astonishing property of WSCP is its stability: Even after an hour of boiling in water it comes out unharmed!
In Arabidopsis WSCP is accumulated specifically in the Septum of the siliquae (Ref.: Bektas et al., 2012). Using recombinant WSCP, we showed that the protein protects its bound chlorophyll very efficiently towards photooxidation although the complex does not contain any carotenoids (Ref.: Schmidt et al., 2003). With its low number of chlorophylls specifically bound, WSCP is an excellent model protein for studying chlorophyll-chlorophyll as well as chlorophyll-protein interactions (Collaboration with Prof. T. Basché, Mainz JGU, Prof. D. Carbonera, Padua, Italy, Prof. J. Pieper, Tartu, Estonia, Prof. T. Renger, Graz, Austria, Dr. F.-J. Schmitt, TU Berlin. Ref.: Theiss et al., 2007; Schmitt et al., 2008; Renger et al., 2009; Pieper et al., 2011; Renger et al., 2011).