© 2005 The Japanese Biochemical Society
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Structural Reorganization of the Copper Binding Site Involving Thr15 of Mavicyanin from Cucurbita pepo medullosa (Zucchini) upon Reduction
1 Department of Materials Chemistry, Graduate School of Engineering, Osaka University, 2-1 Yamada-oka, Suita, Osaka 565-0871; 2 Structure and Function of Biomolecules Group, PRESTO, Japan Science and Technology Agency, 4-1-8 Honcho, Kawaguchi, Saitama 332-0012; and 3 Department of Chemistry, Graduate School of Science, Osaka University, 1-14 Machikaneyama, Toyonaka, Osaka 560-0043
To whom correspondence should be addressed. Tel: +81-6-6879-7408, Fax: +81-6-6879-7409, E-mail: kai{at}chem.eng.osaka-u.ac.jp
Mavicyanin, a glycosylated protein isolated from Cucurbita pepo medullosa (zucchini), is a member of the phytocyanin subfamily containing one polypeptide chain of 109 amino residues and an unusual type-I Cu site in which the copper ligands are His45, Cys86, His91, and Gln96. The crystal structures of oxidized and reduced mavicyanin were determined at 1.6 and 1.9 Å resolution, respectively. Mavicyanin has a core structure of seven polypeptide ß-strands arranged as a ß-sandwich organized into two ß-sheets, and the structure considerably resembles that of stellacyanin from cucumber (CST) or cucumber basic protein (CBP). A flexible region was not observed on superimpositioning of the oxidized and reduced mavicyanin structures. However, the CuII-
-O-Gln96 bond length was extended by 0.47 Å, and the Thr15 residue was rotated by 60.0 degrees and O-
1-Thr15 moved from a distance of 4.78 to 2.58 Å from the ligand Gln96 forming a new hydrogen bond between O-1-Thr15 and -O-Gln96 upon reduction. The reorganization of copper coordination geometry of mavicyanin upon reduction arouses reduction potential decreased above pH 8 [Battistuzzi et al. (2001) J. Inorg. Biochem. 83, 223–227]. The rotation of Thr15 and the hydrogen bonding with the ligand Gln96 may constitute structural evidence of the decrease in the reduction potential at high pH.
* Present address: Department of Chemistry, Faculty of Science, Kanazawa University, Kakuma-machi, Kanazawa 920-1192.