The fuc1 gene product (20 kDa FUC1) of pisum sativum has no α-L-fucosidase activity

An α-L-fucosidase purified from pea (Pisum sativum L. cv Alaska) epicotyl was previously described as a cell wall enzyme of 20 kDa that hydrolyses terminal α-L-fucosidic linkages from oligosaccharide fragments of xyloglucan. cDNA and genomic copies were further isolated and sequenced. The predicted product of the cDNA and the genomic clone (fuc1), was a 20 kDa protein containing a signal peptide and five cysteines. This was the first α-L-fucosidase gene to be cloned in plants but its fucosidase activity has not been demonstrated. Here, our biochemical and immuno analyses suggest that fuc1 does not encode an α-L-fucosidase. Pea fuc1 expressed in Escherichia coli, insect cells and Arabidopsis thaliana produced recombinant proteins without α-L-fucosidase activity. Pea plants had endogenous α-L-fucosidase activity, but the enzyme was not recognised by an antibody produced against recombinant FUC1 protein expressed in E. coli. In contrast, the antibody immunoprecipitated a 20 kDa protein which was inactive. By chromatographic analysis of pea protein extracts, we separated α-L-fucosidase-active fractions from the 20 kDa protein fractions. We conclude that the α-L-fucosidase activity is not attributable to the 20 kDa FUC1 protein. A new function for fuc1 gene product, now named PIP20 (for protease inhibitor from pea) is proposed.