Water-soluble chlorophyll protein in Brassicaceae plants is a stress-induced chlorophyll-binding protein.
Two kinds of water-soluble chlorophyll (Chl) proteins (WSCPs) have been found, e.g., a WSCP from Chenopodium, Atriplex, Polygonum, and Amaranthus species (class I) and that from Brassica, Raphanus, and Lepidium species (class II). Classes I and II WSCPs differ mainly in their photoconvertiblity. Class I WSCPs show a light-induced absorption change, whereas Class II WSCPs do not. The molecular and functional properties of Class I WSCP are largely uncertain. On the other hand, recent studies on the adaptation of plants to osmotic stress revealed the participation of drought-stress induced proteins with molecular masses of 20-22 kDa possessing a sequence similarity with class II WSCPs. This mini review focuses on the molecular signature of class II WSCPs. The physiological function of class II WSCPs has not been clarified either, but, their water-solubility, low Chl content, and stress-inducibility suggested little contribution to photosynthesis. Several molecular properties predicting its physiological role are as follows. The WSCP tetramer, may have only one or no Chl molecules in each subunit. All WSCPs possess a motif for Künitz-type proteinase inhibitor family in their sequence. WSCP is induced by drought- and heat-stresses suggesting its protective role during stress conditions. Monomeric recombinant apo-WSCP is able to remove Chls from the thylakoid membrane in aqueous solution and form into a tetramer. Brassica-WSCP contains a signal sequence targeted to endoplasmic reticulum. The highly conserved, C-terminal region is missing in the mature WSCP. Possible functions of class II WSCPs in plant tissues are discussed.
Satoh
H
H
Department of Biomolecular Science, Toho University, Miyama, Funabashi, Chiba, 274-8510 Japan. hsatoh@biomol.sci.toho-u.ac.jp
Uchida
A
A
Nakayama
K
K
Okada
M
M
D000222:Adaptation, Physiological; D000595:Amino Acid Sequence; D019607:Brassicaceae / Q000235:genetics / Q000378:metabolism*; D002352:Carrier Proteins; D002734:Chlorophyll / Q000378:metabolism*; D045342:Light-Harvesting Protein Complexes; D008969:Molecular Sequence Data; D010455:Peptides; D010788:Photosynthesis; D045322:Photosynthetic Reaction Center Complex Proteins / Q000145:classification / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D010940:Plant Proteins; D016415:Sequence Alignment; D014361:Trypsin Inhibitors / Q000235:genetics / Q000378:metabolism
D002352:Carrier Proteins; C053865:Kunitz-type protease inhibitor, plant; D045342:Light-Harvesting Protein Complexes; D010455:Peptides; D045322:Photosynthetic Reaction Center Complex Proteins; D010940:Plant Proteins; D014361:Trypsin Inhibitors; C115715:WSCP protein, Brassica oleracea; D002734:Chlorophyll