title: A novel main-chain anion-binding site in proteins: the nest. A particular combination of phi,psi values in successive residues gives rise to anion-binding sites that occur commonly and are found often at functionally important regions.
abstract: Main-chain conformations where one amino acid residue can be described as gamma(R) (or alpha(R)) and an adjacent one as gamma(L) (or alpha(L)) mostly result in the three main-chain NH groups (of the two residues and the one following) forming a depression that can accommodate an atom with a whole or partial negative charge. We propose the name nest for this feature. The negatively charged atom, when present, is also stabilized by hydrogen-bonding with the NH groups. In an average protein, 8 % of residues are involved in a nest. The anion, or partially negatively charged atom, that often occupies the nest may be a main-chain carbonyl oxygen atom as in the paperclip, also called the Schellman loop, and the oxyanion hole of serine proteases. It can be a phosphate group, as in the P-loop superfamily that binds ATP and GTP. Overlapping, compound, nests are observed often, as in the P-loop, which has five successive NH groups that bind the beta phosphate group of nucleotide triphosphate. The longest compound nests are found surrounding cysteine-bound [2Fe2S] and [4Fe4S] iron-sulfur centers, which are also anionic; nests may encourage binding of the more reduced forms. The nest is a novel feature in the sense of not having been described as a unique motif with anion-binding potential before, although some of the situations where it occurs are familiar.
authors.affiliation: Division of Biochemistry and Molecular Biology, Institute of Biomedical and Life Sciences, Glasgow University, Glasgow, G12 8QQ, UK.
authors.forename: James D
authors.initials: JD
authors.lastname: Watson
authors.forename: E James
authors.initials: EJ
authors.lastname: Milner-White
mesh_terms: D020816:Amino Acid Motifs; D000838:Anions / Q000737:chemistry / Q000378:metabolism*; D001665:Binding Sites; D002118:Calcium / Q000378:metabolism; D030562:Databases, Protein; D020832:EF Hand Motifs; D006860:Hydrogen Bonding; D007506:Iron-Sulfur Proteins / Q000737:chemistry / Q000378:metabolism; D008958:Models, Molecular; D010710:Phosphates / Q000737:chemistry / Q000378:metabolism; D011485:Protein Binding; D017433:Protein Structure, Secondary; D011506:Proteins / Q000737:chemistry* / Q000378:metabolism*; D012697:Serine Endopeptidases / Q000737:chemistry / Q000378:metabolism
chemical_list: D000838:Anions; D007506:Iron-Sulfur Proteins; D010710:Phosphates; D011506:Proteins; D012697:Serine Endopeptidases; D002118:Calcium