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- Title
Structural and mechanistic insights into a lysosomal membrane enzyme HGSNAT involved in Sanfilippo syndrome.
- Authors
Zhao, Boyang; Cao, Zhongzheng; Zheng, Yi; Nguyen, Phuong; Bowen, Alisa; Edwards, Robert H.; Stroud, Robert M.; Zhou, Yi; Van Lookeren Campagne, Menno; Li, Fei
- Abstract
Heparan sulfate (HS) is degraded in lysosome by a series of glycosidases. Before the glycosidases can act, the terminal glucosamine of HS must be acetylated by the integral lysosomal membrane enzyme heparan-α-glucosaminide N-acetyltransferase (HGSNAT). Mutations of HGSNAT cause HS accumulation and consequently mucopolysaccharidosis IIIC, a devastating lysosomal storage disease characterized by progressive neurological deterioration and early death where no treatment is available. HGSNAT catalyzes a unique transmembrane acetylation reaction where the acetyl group of cytosolic acetyl-CoA is transported across the lysosomal membrane and attached to HS in one reaction. However, the reaction mechanism remains elusive. Here we report six cryo-EM structures of HGSNAT along the reaction pathway. These structures reveal a dimer arrangement and a unique structural fold, which enables the elucidation of the reaction mechanism. We find that a central pore within each monomer traverses the membrane and controls access of cytosolic acetyl-CoA to the active site at its luminal mouth where glucosamine binds. A histidine-aspartic acid catalytic dyad catalyzes the transfer reaction via a ternary complex mechanism. Furthermore, the structures allow the mapping of disease-causing variants and reveal their potential impact on the function, thus creating a framework to guide structure-based drug discovery efforts. HGSNAT is a critical lysosomal membrane enzyme involved in the devastating lysosomal storage disease Sanfilippo syndrome. Here, Zhao et. al. reveal the mechanism for transmembrane acetylation catalyzed by HGSNAT with a series of cryo-EM structures.
- Subjects
SANFILIPPO syndrome; LYSOSOMAL storage diseases; DRUG discovery; ACETYL group; ENZYMES; ACETYLCOENZYME A
- Publication
Nature Communications, 2024, Vol 15, Issue 1, p1
- ISSN
2041-1723
- Publication type
Article
- DOI
10.1038/s41467-024-49614-1