H-1 and N-15 NMR assignment and solution structure of the SH3 domain of spectrin: Comparison of unrefined and refined structure sets with the crystal structure

The assignment of the H-1 and N-15 nuclear magnetic resonance spectra of the Src-homology region 3 domain of chicken brain alpha-spectrin has been obtained. A set of solution structures has been determined from distance and dihedral angle restraints, which provide a reasonable representation of the protein structure in solution, as evaluated by a principal component analysis of the global pairwise root-mean-square deviation (rmsd) in a large set of structures consisting of the refined and unrefined solution structures and the crystal structure. The solution structure is well defined, with a lower degree of convergence between the structures in the loop regions than in the secondary structure elements. The average pairwise rmsd between the 15 refined solution structures is 0.71 +/- 0.13 Angstrom for the backbone atoms and 1.43 +/- 0.14 Angstrom for all heavy atoms, The solution structure is basically the same as the crystal structure. The average rmsd between the 15 refined solution structures and the crystal structure is 0.76 Angstrom for the backbone atoms and 1.45 +/- 0.09 Angstrom for all heavy atoms. There are, however, small differences probably caused by intermolecular contacts in the crystal structure.