High‐resolution structure of an α‐spectrin SH3‐domain mutant with a redesigned hydrophobic core

The α‐spectrin SH3 domain (Spc‐SH3) is a small modular domain which has been broadly used as a model protein in folding studies and these studies have sometimes been supported by structural information obtained from the coordinates of Spc‐SH3 mutants. The structure of B5/D48G, a multiple mutant designed to improve the hydrophobic core and as a consequence the protein stability, has been solved at 1 Å resolution. The crystals belonged to the orthorhombic space group P 2 1 2 1 2 1 , with unit‐cell parameters a = 24.79, b = 37.23, c = 62.95 Å. This mutant also bears a D48G substitution in the distal loop and this mutation has also been reported to increase the stability of the protein by itself. The structure of the B5/D48G mutant shows a highly packed hydrophobic core and a more ordered distal loop compared with previous Spc‐SH3 structures.