title: The bactofilin cytoskeleton protein BacM of Myxococcus xanthus forms an extended β-sheet structure likely mediated by hydrophobic interactions.
abstract: Bactofilins are novel cytoskeleton proteins that are widespread in Gram-negative bacteria. Myxococcus xanthus, an important predatory soil bacterium, possesses four bactofilins of which one, BacM (Mxan_7475) plays an important role in cell shape maintenance. Electron and fluorescence light microscopy, as well as studies using over-expressed, purified BacM, indicate that this protein polymerizes in vivo and in vitro into ~3 nm wide filaments that further associate into higher ordered fibers of about 10 nm. Here we use a multipronged approach combining secondary structure determination, molecular modeling, biochemistry, and genetics to identify and characterize critical molecular elements that enable BacM to polymerize. Our results indicate that the bactofilin-determining domain DUF583 folds into an extended β-sheet structure, and we hypothesize a left-handed β-helix with polymerization into 3 nm filaments primarily via patches of hydrophobic amino acid residues. These patches form the interface allowing head-to-tail polymerization during filament formation. Biochemical analyses of these processes show that folding and polymerization occur across a wide variety of conditions and even in the presence of chaotropic agents such as one molar urea. Together, these data suggest that bactofilins are comprised of a structure unique to cytoskeleton proteins, which enables robust polymerization.
authors: W. Harry Feinstone Department of Molecular Microbiology and Immunology, Johns Hopkins Bloomberg School of Public Health, Baltimore, Maryland, United States of America.
authors: David M
authors: DM
authors: Zuckerman
authors: Department of Biochemistry and Molecular Biology, Johns Hopkins Bloomberg School of Public Health and Johns Hopkins Malaria Research Institute, Baltimore, Maryland, United States of America.
authors: Lauren E
authors: LE
authors: Boucher
authors: W. Harry Feinstone Department of Molecular Microbiology and Immunology, Johns Hopkins Bloomberg School of Public Health, Baltimore, Maryland, United States of America.
authors: Kefang
authors: K
authors: Xie
authors: Department of Structural Biology, Max Planck Institute of Biochemistry, Am Klopferspitz 18, Martinsried, Germany.
authors: Harald
authors: H
authors: Engelhardt
authors: Department of Biochemistry and Molecular Biology, Johns Hopkins Bloomberg School of Public Health and Johns Hopkins Malaria Research Institute, Baltimore, Maryland, United States of America.
authors: Jürgen
authors: J
authors: Bosch
authors: W. Harry Feinstone Department of Molecular Microbiology and Immunology, Johns Hopkins Bloomberg School of Public Health, Baltimore, Maryland, United States of America.
authors: Egbert
authors: E
authors: Hoiczyk
mesh_terms: D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry*; D003598:Cytoskeletal Proteins / Q000737:chemistry*; D057927:Hydrophobic and Hydrophilic Interactions; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016941:Myxococcus xanthus; D055503:Protein Multimerization; D017434:Protein Structure, Tertiary; D017421:Sequence Analysis; D013499:Surface Properties
chemical_list: D001426:Bacterial Proteins; D003598:Cytoskeletal Proteins