Deciphering α-L-Fucosidase Activity Contribution in Human and Mouse: Tissue α-L-Fucosidase FUCA1 Meets Plasma α-L-Fucosidase FUCA2

Fucose-containing glycoproteins and glycolipids broadly occur in humans as well as in many other species and are essential for a wide range of physiological processes, such as cell adhesion, fertilization, and tumor development. In humans, the cellular degradation of various fucosylated glycoconjugates depends on the <i>FUCA1</i>-encoded lysosomal tissue α-L-fucosidase (FUCA1). The crucial role of FUCA1 is reflected by the severe lysosomal storage disease fucosidosis, which causes a massive accumulation of fucosylated glycans, glycolipids, and α(1,6)-fucosylated glycoasparagines. Therefore, it is reasonable to assume that FUCA1 is predominantly responsible for the degradation of fucosylated glycoconjugates, although a second, functionally uncharacterized α-L-fucosidase, the plasma α-L-fucosidase (FUCA2), is known. To investigate the impact of both fucosidases in more detail, we generated two different monoclonal antibodies as useful tools for the detection of human and murine FUCA1 and utilized a FUCA2-specific antibody to demonstrate that FUCA2 is a bona fide lysosomal protein that is sorted in a mannose 6-phosphate (M6P)-dependent manner. We then compared FUCA1 and FUCA2 upon ectopic expression and evaluated their enzyme activity profiles under various conditions. Untagged and differently tagged versions of FUCA1 exhibited α-L-fucosidase activity, while various FUCA2 derivatives, even after affinity purification, did not show any fucosidase activity against commonly used pseudo-substrates. Our findings suggest that FUCA1 and not FUCA2 is exclusively responsible for the lysosomal de-fucosylation of glycoconjugates.