The mistletoe lectin I—Phloretamide structure reveals a new function of plant lectins

• Published in: Biochemical and biophysical research communications Vol. 364; no. 2; pp. 195 - 200
• Main Authors: Meyer, A., Rypniewski, W., Celewicz, L., Erdmann, V.A., Voelter, W., Singh, T.P., Genov, N., Barciszewski, J., Betzel, Ch
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 14.12.2007
• Subjects: Binding Sites; Crystallography, X-Ray; Models, Molecular; Plant growth hormone; Plant Preparations - chemistry; Plant Proteins - chemistry; Protein Binding; Protein Conformation; Protein Subunits - chemistry; Ribosome Inactivating Proteins, Type 2 - chemistry; Santalales; Toxins, Biological - chemistry; Viscum album; Viscum album - chemistry; X-ray analysis; X-ray analysis; Viscum album; Plant growth hormone
• ISSN: 0006-291X; 1090-2104
• DOI: 10.1016/j.bbrc.2007.09.113

The X-ray structure at 2.7 Å resolution of the complex between the European mistletoe lectin I ( Viscum album, ML-I) and the plant growth hormone, 3-( p-hydroxyphenyl)-propionic acid amide (phloretamide, PA) from xylem sap has revealed the binding of PA at the so far undescribed hydrophobic cavity located between the two subunits of this ribosome-inhibiting protein. No such cavity is observed in related lectins. The binding of PA is achieved through interactions with the non-conserved residues Val228A, Leu230A, Arg388B, and the C-terminal Pro510B. It is conceivable that binding of PA to ML-I is part of a defence mechanism of the parasite against the host, whereby the parasite prevents the growth hormone of the host from interfering with its own regulatory system. The specific binding of PA to ML-I indicates that heterodimeric RIPs are multifunctional proteins whose functions in the cell have not yet been fully recognized and analyzed.