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Published on February 27, 2008; 10.1104/pp.107.111500

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Received October 25, 2007
Accepted February 19, 2008

Proteinase Inhibitor from Ginkgo Seeds Is a Member of Plant Nonspecific Lipid Transfer Protein Gene Family

Yoriko Sawano , Ken-ichi Hatano *, Takuya Miyakawa , Hideki Komagata , Yumiko Miyauchi , Hiroshi Yamazaki , and Masaru Tanokura

Department of Applied Biological Chemistry, Graduate School of Agricultural and Life Sciences, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan; Department of Biological Sciences, Faculty of Engineering, Gunma University, 1-5-1 Tenjin-cho, Kiryu, Gunma 376-8515, Japan

* Corresponding author; email: hatano{at}chem-bio.gunma-u.ac.jp.

A 9-kDa proteinase inhibitor was isolated from the seeds of Ginkgo biloba and purified to homogeneity. This protein was revealed to partial-noncompetitively inhibit the aspartic-acid proteinase pepsin and the cysteine proteinase papain (Ki = 10-5–10-4 M). The cDNA of the inhibitor was revealed to contain a 357-bp open reading frame encoding a 119-amino acid protein with a potential signal peptide (27 residues), indicating that this protein is synthesized as a preprotein and secreted outside the cells. Semi-quantitative RT-PCR revealed that this gene expresses only in seeds, not in stems, leaves, and roots, suggesting that the protein is involved in seed development and/or germination. The inhibitor showed about 40% sequence homology with type-I nonspecific lipid transfer proteins (nsLTP1s) from other plant species. Actually, this inhibitor exerted both lipid transfer activity and lipid binding activity, while the protein did not show any antifungal and antibacterial activities. Furthermore, the site-directed mutagenesis study using a recombinant ginkgo nsLTP1 revealed that Pro79 and Phe80 are important on phospholipid transfer activity and that Pro79 and Ile82 are essential for the binding activity towards cis-unsaturated fatty acids. On the other hand, the {alpha}-helical content of P79A and F80A mutants was significantly lower than that of the wild-type protein. It was noteworthy noting that the papain-inhibitory activity of P79A and F80A mutants was elevated twice as much as the wild-type protein. In summary, we concluded that the Pro79 residue plays a critical role in both the lipid transfer and binding activities of ginkgo nsLTP1.




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