Purification and partial characterization of the lectin from the marine red alga Tichocarpus crinitus (Gmelin) Rupr. (Rhodophyta)

Abstract

A new lectin from the red alga Tichocarpus crinitus (TCL) was purified and partially characterized. The purification procedure consisted of extracting soluble proteins with 0.025 M Tris-HCl buffer (pH 7.5), followed by ammonium sulphate precipitation (75% saturation), hydrophobic interaction chromatography on phenyl-Sepharose and gel filtration chromatography on Superdex 75 HR 10/30. TCL is a monomeric protein with a relative molecular weight of 41,000, as shown by gel filtration and sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) in the presence and absence of b-mercaptoethanol. Isoelectric focusing showed that TCL is an acidic protein with an isoelectric point (pI) of 4.93, and analysis of its amino acid composition revealed high contents of acidic amino acids (aspartic and glutamic acids), serine, threonine, proline and alanine. Its activity was not inhibited by any of the monosaccharides tested, but was inhibited by the complex glycoproteins porcine stomach mucin (type VII) (PSM) and fetuin, and was independent of divalent cations. The carbohydrate content of 6.9% suggested that the lectin is a glycoprotein. TCL had a weak mitogenic effect on human lymphocytes and an ability to stimulate synthesis of pro-inflammatory cytokines TNF-a, IFN-g, IL-6 by human whole-blood cells.