Solution structure of the spectrin repeat: a left-handed antiparallel triple-helical coiled-coil.
Cytoskeletal proteins belonging to the spectrin family have an elongated structure composed of repetitive units. The three-dimensional solution structure of the 16th repeat from chicken brain alpha-spectrin (R16) has been determined by NMR spectroscopy and distance geometry-simulated annealing calculations. We used a total of 1035 distance restraints, which included 719 NOE-based values obtained by applying the ambiguous restraints for iterative assignment (ARIA) method. In addition, we performed a direct refinement against 1H-chemical shifts. The final ensemble of 20 structures shows an average RMSD of 1.52 A from the mean for the backbone atoms, excluding loops and N and C termini. R16 is made up of three antiparallel alpha-helices separated by two loops, and folds into a left-handed coiled-coil. The basic unit of spectrin is an antiparallel heterodimer composed of two homologous chains, beta and alpha. These assemble a tetramer via a mechanism that relies on the completion of a single repeat by association of the partial repeats located at the C terminus of the beta-chain (two helices) and at the N terminus of the alpha-chain (one helix). This tetramer is the assemblage able to cross-link actin filaments. Model building by homology of the "tetramerization" repeat from human erythrocyte spectrin illuminates the possible role of point mutations which cause hemolytic anemias.
Pascual
J
J
European Molecular Biology Laboratory, Meyerhofstr. 1, Heidelberg, 69012, Germany.
Pfuhl
M
M
Walther
D
D
Saraste
M
M
Nilges
M
M
D000595:Amino Acid Sequence; D000818:Animals; D002645:Chickens; D006801:Humans; D008969:Molecular Sequence Data; D019906:Nuclear Magnetic Resonance, Biomolecular; D011487:Protein Conformation; D017510:Protein Folding; D017386:Sequence Homology, Amino Acid; D012996:Solutions; D013049:Spectrin / Q000737:chemistry*
D012996:Solutions; D013049:Spectrin