title: Solution structure of the fibronectin type III domain from Bacillus circulans WL-12 chitinase A1.
abstract: Growing evidence suggests that horizontal gene transfer plays an integral role in the evolution of bacterial genomes. One of the debated examples of horizontal gene transfer from animal to prokaryote is the fibronectin type III domain (FnIIID). Certain extracellular proteins of soil bacteria contain an unusual cluster of FnIIIDs, which show sequence similarity to those of animals and are likely to have been acquired horizontally from animals. Here we report the solution structure of the FnIIID of chitinase A1 from Bacillus circulans WL-12. To the best of our knowledge, this is the first tertiary structure to be reported for an FnIIID from a bacterial protein. The structure of the domain shows significant similarity to FnIIIDs from animal proteins. Sequence comparisons with FnIIIDs from other soil bacteria proteins show that the core-forming residues are highly conserved and, thus, are under strong evolutionary pressure. Striking similarities in the tertiary structures of bacterial FnIIIDs and their mammalian counterparts may support the hypothesis that the evolution of the FnIIID in bacterial carbohydrases occurred horizontally. The total lack of surface-exposed aromatic residues also suggests that the role of this FnIIID is different from those of other bacterial beta-sandwich domains, which function as carbohydrate-binding modules.
authors.affiliation: Graduate School of Biological Sciences, Nara Institute of Science and Technology, 8916-5 Takayama, Ikoma, Nara 630-0101, Japan.
authors.forename: Jun-Goo
authors.initials: JG
authors.lastname: Jee
authors.forename: Takahisa
authors.initials: T
authors.lastname: Ikegami
authors.forename: Masayuki
authors.initials: M
authors.lastname: Hashimoto
authors.forename: Takeshi
authors.initials: T
authors.lastname: Kawabata
authors.forename: Mitsunori
authors.initials: M
authors.lastname: Ikeguchi
authors.forename: Takeshi
authors.initials: T
authors.lastname: Watanabe
authors.forename: Masahiro
authors.initials: M
authors.lastname: Shirakawa
mesh_terms: D000595:Amino Acid Sequence; D001407:Bacillus / Q000737:chemistry / Q000201:enzymology* / Q000235:genetics; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics; D002688:Chitinases / Q000737:chemistry* / Q000235:genetics; D005353:Fibronectins / Q000737:chemistry* / Q000235:genetics; D006860:Hydrogen Bonding; D008958:Models, Molecular; D008969:Molecular Sequence Data; D019906:Nuclear Magnetic Resonance, Biomolecular; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics; D016415:Sequence Alignment
chemical_list: D001426:Bacterial Proteins; D005353:Fibronectins; D011994:Recombinant Proteins; D002688:Chitinases