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Publication Abstract from PubMed

The bifunctional L-fucokinase/GDP-beta-L-fucose pyrophosphorylase (FKP) from Bacteroides fragilis catalyzes the conversion from L-fucose to GDP-beta-L-fucose. The reaction product, representing the activated form of L-fucose, is used by all L-fucosyltransferases to incorporate L-fucose. Herein we report the first X-ray crystal structures of FKP in complex with substrate/product, leading to the dissection of both activity domains and corresponding catalytic mechanisms. The full length (FKP-FL, 949 amino acids) exists as a tetramer in solution, but the individually prepared N-terminal domain (FKP-NTD corresponding to the sequence 1-496, also containing a SUMO tag) and C-terminal (FKP-CTD, the sequence 519-949) form a monomer and a dimer, respectively. FKP-NTD has a single alpha/beta domain and a beta-helix-containing domain, whereas FKP-CTD folds into two alpha/beta domains and the linker comprises three alpha-helices. The beta-L-fucose-1-phosphate (fucose-1-P) and GTP bound separately to the active sites of fucokinase (located at FKP-CTD) and pyrophosphorylase (FKP-NTD), and a third nucleotide binding site is adjacent to the beta-helix (also in FKP-NTD). Furthermore, Asp762 was proposed to serve as the general base in the reaction of fucokinase, to deprotonate the C1-OH of fucose in the nucleophilic attack to gamma-phosphate of ATP, resulting in the formation of fucose-1-P. At the same time, Arg592 and magnesium ion stabilize the developing negative charge in the leaving group (ADP). Subsequently, in the pyrophosphorylase-catalyzed reaction, the Lys187 side chain facilitates the nucleophilic attack of fucose-1-P toward GTP, leading to the formation of GDP-fucose.

Structural Insight into the Catalytic Mechanism of the Bifunctional Enzyme L-Fucokinase/GDP-fucose Pyrophosphorylase.,Lin SW, Ko TP, Chiang HY, Wu CG, Hsu MF, Wang AH, Lin CH J Biol Chem. 2025 Feb 22:108344. doi: 10.1016/j.jbc.2025.108344. PMID:39993526^[2]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.