title: Structural basis for fragmenting the exopolysaccharide of Acinetobacter baumannii by bacteriophage ΦAB6 tailspike protein.
abstract: With an increase in antibiotic-resistant strains, the nosocomial pathogen Acinetobacter baumannii has become a serious threat to global health. Glycoconjugate vaccines containing fragments of bacterial exopolysaccharide (EPS) are an emerging therapeutic to combat bacterial infection. Herein, we characterize the bacteriophage ΦAB6 tailspike protein (TSP), which specifically hydrolyzed the EPS of A. baumannii strain 54149 (Ab-54149). Ab-54149 EPS exhibited the same chemical structure as two antibiotic-resistant A. baumannii strains. The ΦAB6 TSP-digested products comprised oligosaccharides of two repeat units, typically with stoichiometric pseudaminic acid (Pse). The 1.48-1.89-Å resolution crystal structures of an N-terminally-truncated ΦAB6 TSP and its complexes with the semi-hydrolyzed products revealed a trimeric β-helix architecture that bears intersubunit carbohydrate-binding grooves, with some features unusual to the TSP family. The structures suggest that Pse in the substrate is an important recognition site for ΦAB6 TSP. A region in the carbohydrate-binding groove is identified as the determinant of product specificity. The structures also elucidated a retaining mechanism, for which the catalytic residues were verified by site-directed mutagenesis. Our findings provide a structural basis for engineering the enzyme to produce desired oligosaccharides, which is useful for the development of glycoconjugate vaccines against A. baumannii infection.
authors.affiliation: Institute of Biochemical Sciences, National Taiwan University, Taipei 106, Taiwan.|Institute of Biological Chemistry, Academia Sinica, Taipei 115, Taiwan.
authors.forename: I-Ming
authors.initials: IM
authors.lastname: Lee
authors.affiliation: Institute of Biological Chemistry, Academia Sinica, Taipei 115, Taiwan.
authors.forename: I-Fan
authors.initials: IF
authors.lastname: Tu
authors.affiliation: Institute of Biological Chemistry, Academia Sinica, Taipei 115, Taiwan.
authors.forename: Feng-Ling
authors.initials: FL
authors.lastname: Yang
authors.affiliation: Institute of Biological Chemistry, Academia Sinica, Taipei 115, Taiwan.|Core Facilities for Protein Structural Analysis (CFPSA), Academia Sinica, Taipei 115, Taiwan.
authors.forename: Tzu-Ping
authors.initials: TP
authors.lastname: Ko
authors.affiliation: Institute of Biological Chemistry, Academia Sinica, Taipei 115, Taiwan.
authors.forename: Jiahn-Haur
authors.initials: JH
authors.lastname: Liao
authors.affiliation: Master program in Microbiology and Immunology, Tzu Chi University, Hualien 970, Taiwan.
authors.forename: Nien-Tsung
authors.initials: NT
authors.lastname: Lin
authors.affiliation: Genomics Research Center, Academia Sinica, Taipei 115, Taiwan.
authors.forename: Chung-Yi
authors.initials: CY
authors.lastname: Wu
authors.affiliation: Genomics Research Center, Academia Sinica, Taipei 115, Taiwan.
authors.forename: Chien-Tai
authors.initials: CT
authors.lastname: Ren
authors.affiliation: Institute of Biological Chemistry, Academia Sinica, Taipei 115, Taiwan.|Core Facilities for Protein Structural Analysis (CFPSA), Academia Sinica, Taipei 115, Taiwan.
authors.forename: Andrew H-J
authors.initials: AH
authors.lastname: Wang
authors.affiliation: Institute of Biological Chemistry, Academia Sinica, Taipei 115, Taiwan.
authors.forename: Ching-Ming
authors.initials: CM
authors.lastname: Chang
authors.affiliation: Institute of Biological Chemistry, Academia Sinica, Taipei 115, Taiwan.|Core Facilities for Protein Structural Analysis (CFPSA), Academia Sinica, Taipei 115, Taiwan.
authors.forename: Kai-Fa
authors.initials: KF
authors.lastname: Huang
authors.affiliation: Institute of Biochemical Sciences, National Taiwan University, Taipei 106, Taiwan.|Institute of Biological Chemistry, Academia Sinica, Taipei 115, Taiwan.|Department of Chemistry, National Taiwan University, Taipei 106, Taiwan.
authors.forename: Shih-Hsiung
authors.initials: SH
authors.lastname: Wu
mesh_terms: D040981:Acinetobacter baumannii / Q000821:virology; D001665:Binding Sites; D006026:Glycoside Hydrolases; D062105:Molecular Docking Simulation; D009844:Oligosaccharides / Q000737:chemistry; D011135:Polysaccharides, Bacterial / Q000737:chemistry* / Q000378:metabolism; D011485:Protein Binding; D017376:Viral Tail Proteins / Q000737:chemistry* / Q000378:metabolism
chemical_list: D009844:Oligosaccharides; D011135:Polysaccharides, Bacterial; D017376:Viral Tail Proteins; D006026:Glycoside Hydrolases; C083268:tailspike protein, bacteriophage