title: Conformational changes at the tetramerization site of erythroid alpha-spectrin upon binding beta-spectrin: a spin label EPR study.
abstract: We used cysteine scanning, isothermal titration calorimetry (ITC) and spin label EPR methods to study the two regions that flank the partial domain Helix C' of the N-terminal end of alpha-spectrin (residues 14-20 and residues 44-54) in the absence and presence of a model protein of the beta-spectrin C-terminal end. In the absence of beta-spectrin, residues 14-20 and 46-52 were known to be unstructured. The EPR spectral values of the inverse line width (Delta H (-1)) and of the width between the low field peak and the central peak ( aZ) of residues in part of the first unstructured region (residues 17-20) and of most residues in the second unstructured junction region (residues 46-52) changed dramatically upon association with beta-spectrin, suggesting that the two regions undergo a conformational change, becoming more rigid and likely becoming helical. ITC results showed that three of the seven residues in the junction region (residues 46-52) were very important in its association with beta-spectrin, in the following order: L49 > G46 > K48. In general, our results suggest that any mutations that affect the propensity of helical formation in the region spanning residues 17-52 in alpha-spectrin, or that affect hydrophobic clustering and/or salt-bridge stabilization of the bundled helices, would affect spectrin tetramer formation, and may lead to blood disorders.
authors.affiliation: Department of Chemistry, University of Illinois at Chicago, 845 West Taylor Street, MC 111, Chicago, Illinois 60607, USA.
authors.forename: Chloe
authors.initials: C
authors.lastname: Antoniou
authors.forename: Vinh Q
authors.initials: VQ
authors.lastname: Lam
authors.forename: L W-M
authors.initials: LW
authors.lastname: Fung
mesh_terms: D000818:Animals; D002151:Calorimetry / Q000379:methods; D019281:Dimerization; D004578:Electron Spin Resonance Spectroscopy / Q000379:methods*; D004912:Erythrocytes / Q000378:metabolism*; D006801:Humans; D008958:Models, Molecular; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D013049:Spectrin / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism
chemical_list: D013049:Spectrin
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