title: The role of nonconserved residues of Archaeoglobus fulgidus ferritin on its unique structure and biophysical properties.
abstract: Archaeoglobus fulgidus ferritin (AfFtn) is the only tetracosameric ferritin known to form a tetrahedral cage, a structure that remains unique in structural biology. As a result of the tetrahedral (2-3) symmetry, four openings (∼45 Å in diameter) are formed in the cage. This open tetrahedral assembly contradicts the paradigm of a typical ferritin cage: a closed assembly having octahedral (4-3-2) symmetry. To investigate the molecular mechanism affecting this atypical assembly, amino acid residues Lys-150 and Arg-151 were replaced by alanine. The data presented here shed light on the role that these residues play in shaping the unique structural features and biophysical properties of the AfFtn. The x-ray crystal structure of the K150A/R151A mutant, solved at 2.1 Å resolution, indicates that replacement of these key residues flips a "symmetry switch." The engineered molecule no longer assembles with tetrahedral symmetry but forms a typical closed octahedral ferritin cage. Small angle x-ray scattering reveals that the overall shape and size of AfFtn and AfFtn-AA in solution are consistent with those observed in their respective crystal structures. Iron binding and release kinetics of the AfFtn and AfFtn-AA were investigated to assess the contribution of cage openings to the kinetics of iron oxidation, mineralization, or reductive iron release. Identical iron binding kinetics for AfFtn and AfFtn-AA suggest that Fe(2+) ions do not utilize the triangular pores for access to the catalytic site. In contrast, relatively slow reductive iron release was observed for the closed AfFtn-AA, demonstrating involvement of the large pores in the pathway for iron release.
authors.affiliation: From the School of Chemical & Biomedical Engineering, Division of Bioengineering, Nanyang Technological University, Singapore 637457.
authors.forename: Barindra
authors.initials: B
authors.lastname: Sana
authors.affiliation: the Howard Hughes Medical Institute, Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125.
authors.forename: Eric
authors.initials: E
authors.lastname: Johnson
authors.affiliation: Rigaku Americas, The Woodlands, Texas 77381-5209.
authors.forename: Pierre
authors.initials: P
authors.lastname: Le Magueres
authors.affiliation: Rigaku Americas, The Woodlands, Texas 77381-5209.
authors.forename: Angela
authors.initials: A
authors.lastname: Criswell
authors.affiliation: UCLA-Department of Energy, Institute for Genomics and Proteomics, Los Angeles, California 90095-1570. Electronic address: cascio@mbi.ucla.edu.
authors.forename: Duilio
authors.initials: D
authors.lastname: Cascio
authors.affiliation: From the School of Chemical & Biomedical Engineering, Division of Bioengineering, Nanyang Technological University, Singapore 637457,. Electronic address: slim@ntu.sg.
authors.forename: Sierin
authors.initials: S
authors.lastname: Lim
mesh_terms: D019943:Amino Acid Substitution; D019843:Archaeal Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D019611:Archaeoglobus fulgidus / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D018360:Crystallography, X-Ray; D005293:Ferritins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D007501:Iron / Q000737:chemistry* / Q000378:metabolism; D011485:Protein Binding; D020836:Protein Structure, Quaternary; D013329:Structure-Activity Relationship
chemical_list: D019843:Archaeal Proteins; D005293:Ferritins; D007501:Iron
keywords: Archaea; Archaeoglobus fulgidus; Enzyme Kinetics; Ferritin; Mutant; Protein Engineering; Protein Nanocage
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