Primary structure of a fucose-specific lectin obtained from a mushroom, Aleuria aurantia

Aleuria aurantia lectin (AAL) is a protein composed of two identical subunits having no carbohydrate chain and shows sugar-binding specificity for L-fucose. Full-length cDNA encoding for the lectin has been isolated from a lambda gt11 library, screened with an antiserum directed against AAL. The cDNA clone contained 1,370 nucleotides and an open reading frame of 939 nucleotides encoding 313 amino acids. The amino-terminal sequence (residues 1-30) of the lectin isolated from the mushroom coincided with the deduced amino acid sequence starting from proline at the 2nd residue, indicating that the mature AAL consists of 312 amino acids. Its molecular weight is calculated to be 33,398. The deduced amino acid sequence shows that AAL includes six internal homologous regions, and has considerable homology with a hemagglutinin from a Gram-negative bacterium, Myxococcus xanthus, which forms a fruiting body. No significant homology was observed with higher plant or animal lectins. The recombinant AAL produced by Escherichia coli JM109 carrying the AAL expression plasmid pKA-1 [Fukumori, F. et al. (1989) FEBS Lett. 250, 153-156] was purified from the cell lysate by affinity chromatography using a fucose-starch column, and hundreds of milligrams of the lectin was obtained. The recombinant lectin showed the same biochemical characteristics and sugar binding specificity as did the natural AAL.