A new mistletoe Phthirusa pyrifolia leaf lectin with antimicrobial properties

Phthirusa pyrifolia leaf lectin (PpyLL) was obtained from the hemi-parasitic medicinal plant mistletoe through saline saturation and two consecutive chromatographic steps on Sephadex G-100 and ion exchange on CM-cellulose. SDS-PAGE of the protein under non-reducing conditions revealed a monomeric protein with a molecular weight of 15.6 kDa. Under reducing conditions in the presence of 2-mercaptoethanol, the protein showed two bands with molecular weights of 15 and 7 kDa. PpyLL, an acidic glycoprotein with 19% sugar content, was not dependent on divalent cations. It was stable up to 70 °C and exhibited maximum hemagglutination at pH 7.5. Lectin fluorescence emission spectra at different temperatures showed that the lectin fluorescence increased when the temperature increased. PpyLL showed a unique affinity for the phosphate derivative of fructose, fructose-1-6-biphosphate. PpyLL showed effective antimicrobial activities against bacteria (Gram-positive: Staphylococcus epidermidis, Streptococcus faecalis and Bacillus subtilis; Gram-negative: Klebsiella pneumoniae) and fungi (Fusarium lateritium and Rhizoctonia solani). Therefore, PpyLL specificity, as determined by a new sugar affinity, may be significant to determine its biological potential.