Purification of a secreted lectin from Andrias davidianus skin and its antibacterial activity.

A lectin secreted from Andrias davidianus skin (ADL) was purified by affinity chromatography on porcine stomach mucin (type III) (PSM)-crosslinked albumin, followed by gel filtration on Sephadex G-100 and HPLC on TSK gel G3000PWXL. The purified lectin was found to be a dimeric protein, as revealed by SDS-PAGE and MALDI-TOF analysis. SDS-PAGE showed that the ADL protein had a molecular mass of 17kDa. ADL produced an 8.5kDa band when examined using SDS-PAGE under reducing conditions. ADL agglutinated native and trypsinized human B erythrocytes. The hemagglutination activity was inhibited by glycoproteins, such as PSM and asialo-PSM, but not by any of the monosaccharides tested. The activity was stable between 4°C and 50°C. Significant ADL activity was observed between pH4–5. The lectin reaction did not depend on the presence of the divalent cation Ca2+ or Mg2+. The N-terminal ADL sequence was determined to be VGYTVGATPM. The lectin exhibited antibacterial activity, involving growth and respiration inhibition in Escherichia coli, Enterobacter aerogenes, Staphylococcus aureus, Bacillus subtilis and Shewanella sp. Furthermore, ADL showed inhibition activity against the yeast Saccharomyces cerevisiae. These findings suggest that ADL plays an important role in the innate immunity of A. davidianus on the body surface.