title: Unusual helix-containing greek keys in development-specific Ca(2+)-binding protein S. 1H, 15N, and 13C assignments and secondary structure determined with the use of multidimensional double and triple resonance heteronuclear NMR spectroscopy.
abstract: Multidimensional heteronuclear NMR spectroscopy has been used to determine almost complete backbone and side-chain 1H, 15N, and 13C resonance assignments of calcium loaded Myxococcus xanthus protein S (173 residues). Of the range of constant-time triple resonance experiments recorded, HNCACB and CBCA(CO)NH, which correlate C alpha and C beta with backbone amide resonances of the same and the succeeding residue respectively, proved particularly useful in resolving assignment ambiguities created by the 4-fold internal homology of the protein S amino acid sequence. Extensive side-chain 1H and 13C assignments have been obtained by analysis of HCCH-TOCSY and 15N-edited TOCSY-HMQC spectra. A combination of NOE, backbone amide proton exchange, 3JNH alpha coupling constant, and chemical shift data has been used to show that each of the protein S repeat units consists of four beta-strands in a Greek key arrangement. Two of the Greek keys contain a regular alpha-helix between the third and fourth strands, resulting in an unusual and possibly unique variation on this common folding motif. Despite similarity between two nine-residue stretches in the first and third domains of protein S and one of the Ca(2+)-binding sequences in bovine brain calmodulin [Inouye, S., Franceschini, T., & Inouye, M. (1983) Proc. Natl. Acad. Sci. U.S.A. 80, 6829-6833], the protein S topology in these regions is incompatible with an EF-hand calmodulin-type Ca(2+)-binding site.
authors.affiliation: Division of Molecular and Structural Biology, Ontario Cancer Institute, Toronto, Canada.
authors.forename: S
authors.initials: S
authors.lastname: Bagby
authors.forename: T S
authors.initials: TS
authors.lastname: Harvey
authors.forename: L E
authors.initials: LE
authors.lastname: Kay
authors.forename: S G
authors.initials: SG
authors.lastname: Eagle
authors.forename: S
authors.initials: S
authors.lastname: Inouye
authors.forename: M
authors.initials: M
authors.lastname: Ikura
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry*; D002135:Calcium-Binding Proteins / Q000737:chemistry*; D003459:Crystallins / Q000737:chemistry; D006860:Hydrogen Bonding; D009682:Magnetic Resonance Spectroscopy; D008969:Molecular Sequence Data; D016941:Myxococcus xanthus / Q000737:chemistry*; D017433:Protein Structure, Secondary; D011994:Recombinant Proteins; D012996:Solutions
chemical_list: D001426:Bacterial Proteins; D002135:Calcium-Binding Proteins; D003459:Crystallins; C046032:Myxococcus spore coat proteins; D011994:Recombinant Proteins; D012996:Solutions