title: A Physicochemical and Mutational Analysis of Intersubunit Interactions of Escherichia coli Ferritin A.
abstract: Ferritin A from Escherichia coli (EcFtnA) is 24-meric protein, which forms spherical cagelike structures called nanocages. The nanocage structure is stabilized by the interface around 4-, 3-, and 2-fold symmetric axes. The subunit structure of EcFtnA comprises a four-helix bundle (helices A-D) and an additional helix E, which forms a 4-fold axis. In this study, we examined the contribution of the interface around three symmetric axes. pH-induced dissociation experiments monitored by analytical ultracentrifugation and small-angle X-ray scattering showed that the dimer related by 2-fold symmetry is the most stable unit. Mutations located near the 3-fold axis revealed that the contribution of each interaction was small. A mutant lacking helix E at the 4-fold axis formed a nanocage, suggesting that helix E is not essential for nanocage formation. Further truncation of the C-terminus of helix D abrogated the formation of the nanocage, suggesting that a few residues located at the C-terminus of helix D are critical for this process. These properties are similar to those known for mammalian ferritins and seem to be common principles for nanocage formation. The difference between EcFtnA and mammalian ferritins was that helix E-truncated EcFtnA maintained an iron-incorporating ability, whereas mammalian mutants lost it.
authors.affiliation: Department of Bioinformatics, Soka University , 1-236 Tangi-cho, Hachioji, Tokyo 192-8577, Japan.
authors.forename: Hideaki
authors.initials: H
authors.lastname: Ohtomo
authors.affiliation: Department of Bioinformatics, Soka University , 1-236 Tangi-cho, Hachioji, Tokyo 192-8577, Japan.
authors.forename: Mio
authors.initials: M
authors.lastname: Ohtomo
authors.affiliation: Department of Bioinformatics, Soka University , 1-236 Tangi-cho, Hachioji, Tokyo 192-8577, Japan.
authors.forename: Daisuke
authors.initials: D
authors.lastname: Sato
authors.affiliation: Department of Bioinformatics, Soka University , 1-236 Tangi-cho, Hachioji, Tokyo 192-8577, Japan.
authors.forename: Atsushi
authors.initials: A
authors.lastname: Kurobe
authors.affiliation: Department of Bioinformatics, Soka University , 1-236 Tangi-cho, Hachioji, Tokyo 192-8577, Japan.
authors.forename: Ayumi
authors.initials: A
authors.lastname: Sunato
authors.affiliation: Department of Physics, Kansai Medical University , 18-89 Uyama-Higashi, Hirakata 573-1136, Japan.
authors.forename: Yoshitaka
authors.initials: Y
authors.lastname: Matsumura
authors.affiliation: Department of Physics, Kansai Medical University , 18-89 Uyama-Higashi, Hirakata 573-1136, Japan.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Kihara
authors.affiliation: Department of Bioinformatics, Soka University , 1-236 Tangi-cho, Hachioji, Tokyo 192-8577, Japan.
authors.forename: Kazuo
authors.initials: K
authors.lastname: Fujiwara
authors.affiliation: Department of Bioinformatics, Soka University , 1-236 Tangi-cho, Hachioji, Tokyo 192-8577, Japan.
authors.forename: Masamichi
authors.initials: M
authors.lastname: Ikeguchi
mesh_terms: D000595:Amino Acid Sequence; D018360:Crystallography, X-Ray; D004926:Escherichia coli / Q000737:chemistry* / Q000235:genetics* / Q000378:metabolism; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000235:genetics* / Q000378:metabolism; D005293:Ferritins / Q000737:chemistry* / Q000235:genetics* / Q000378:metabolism; D007501:Iron / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D049329:Nanostructures / Q000737:chemistry*; D011489:Protein Denaturation; D055503:Protein Multimerization; D017433:Protein Structure, Secondary; D021122:Protein Subunits / Q000737:chemistry / Q000235:genetics / Q000378:metabolism
chemical_list: D029968:Escherichia coli Proteins; D021122:Protein Subunits; C534454:ferritin A, E coli; D005293:Ferritins; D007501:Iron