Isolation and characterization of a galactose-specific lectin (EantH) with antimicrobial activity from Euphorbia antiquorum L. latex

A homodimeric 75 kDa lectin with hemagglutination activity (HA) was purified from the crude latex of Euphorbia antiquorum L. by two types of chromatography, on cation exchange (HiTrap SP FF) and hydrophobic HiTrap Phenyl FF (high sub) columns. The purified protein was designated EantH, and is classified as a galactose-specific thermostable lectin. The HA of EantH was stable at pH values of 5-9 and temperature 5-65 °C. The lectin had bacteriostatic action on the Gram-positive bacteria Staphylococcus aureus and S. epidermidis, with a minimum inhibitory concentration (MIC) of 2000 μg/ml and on a Gram-negative bacterium Samonella typhimurium, with a MIC of 1000 μg/ml. EantH inhibited the growth of Propionibacterium acnes and Streptococcus agalactiae with MIC of 125 μg/ml and 250 μg/ml, respectively. EantH killed P. acnes and S. agalactiae with a minimum microbicidal concentration (MMC) of 1000 μg/ml and 2000 μg/ml, respectively. Scanning electron microscopy indicated that binding of EantH to the carbohydrates in the cell walls of P. acnes and S. typhimurium drastically altered the bacterial cells, and led to inhibition of growth and/or cell death. The antimicrobial activity of EantH could be neutralized by d‑galactose, indicating that its bactericidal action involves binding to galactose in the cell wall.