Cysteine-2 and Cys30 are essential for chlorophyll-binding activity of the water-soluble chlorophyll-binding protein (WSCP) of Chenopodium album
Takahashi, S.; Seki, Y.; Uchida, A.; Nakayama, K.; Satoh, H.
Bioscience Biotechnology and Biochemistry 78(11): 1825-1832
ISSN/ISBN: 0916-8451 PMID: 25060234 DOI: 10.1080/09168451.2014.940274
Chenopodium album has a non-photosynthetic chlorophyll protein known as the water-soluble chlorophyll (Chl)-binding protein (WSCP). The C. album WSCP (CaWSCP) is able to photoconvert the chlorin skeleton of Chl a into a bacteriochlorin-like skeleton. Reducing reagents such as β-mercaptoethanol or dithiothreitol inhibit photoconversion, indicating that S-S bridge(s) in CaWSCP are quite important for it. Recently, we found that the mature region of CaWSCP contains five cysteine residues; Cys2, Cys30, Cys48, Cys63, and Cys144. To identify which cysteine residues are involved in the photoconversion, we generated five mutants (C2S, C30S, C48S, C63S, and C144S) by site-directed mutagenesis. Interestingly, C48S, C63S, and C144S mutants showed the same Chl-binding activity and photoconvertibility as those of the recombinant wild-type CaWSCP-His, while the C2S and C30S mutants completely lost Chl-binding activity. Our findings indicated that the S-S bridge between Cys2 and Cys30 in each CaWSCP subunit is essential for Chl-binding activity.