Cryo-EM structures of human fucosidase FucA1 reveal insight into substrate recognition and catalysis.

Enzymatic hydrolysis of α-L-fucose from fucosylated glycoconjugates is consequential in bacterial infections and the neurodegenerative lysosomal storage disorder fucosidosis. Understanding human α-L-fucosidase catalysis, in an effort toward drug design, has been hindered by the absence of three-dimensional structural data for any animal fucosidase. Here, we have used cryoelectron microscopy (cryo-EM) to determine the structure of human lysosomal α-L-fucosidase (FucA1) in both an unliganded state and in complex with the inhibitor deoxyfuconojirimycin. These structures, determined at 2.49 Å resolution, reveal the homotetrameric structure of FucA1, the architecture of the catalytic center, and the location of both natural population variations and disease-causing mutations. Furthermore, this work has conclusively identified the hitherto contentious identity of the catalytic acid/base as aspartate-276, representing a shift from both the canonical glutamate acid/base residue and a previously proposed glutamate residue. These findings have furthered our understanding of how FucA1 functions in both health and disease. [Display omitted] • Cryo-EM structure of FucA1 resolves debate over the catalytic mechanism • Aspartate 276, which is conserved for all animal homologs, is the catalytic acid/base • A misfolded FucA1 disease variant (S150F) is stabilized by an iminosugar inhibitor Human lysosomal fucosidase (FucA1) recycles fucosylated glycans. Aberrations in the enzyme result in fucosidosis. Armstrong et al. use single-particle cryo-EM to resolve the contentious mechanism of this enzyme. They also demonstrate stabilization of a misfolded variant by deoxyfuconojirimycin and determine how FucA1 accommodates this inhibitor. [ABSTRACT FROM AUTHOR]