Byeon In-Ja L, Louis John M, Gronenborn Angela M
Laboratory of Chemical Physics, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Building 5, Room 130, Bethesda, MD 20892, USA.
J Mol Biol. 2003 Oct 10;333(1):141-52. doi: 10.1016/s0022-2836(03)00928-8.
Immunoglobulin-binding domain B1 of streptococcal protein G (GB1), a small (56 residues), stable, single-domain protein, is one of the most extensively used model systems in the area of protein folding and design. Recently, NMR and X-ray structures of a quintuple GB1 core mutant (L5V/A26F/F30V/Y33F/A34F) that showed an unexpected, intertwined tetrameric architecture were determined. Here, we report the NMR structure of another mutant, derived from the tetramer by reverting the single amino acid position F26 back to the wild-type sequence A26. The structure reveals a domain-swapped dimer that involves exchange of the second beta-hairpin. The resulting overall structure comprises an eight-stranded beta-sheet whose concave side is covered by two alpha helices. The dimer dissociates into a partially folded, monomeric species with a dissociation constant of 93(+/-10)microM.
链球菌蛋白G（GB1）的免疫球蛋白结合结构域B1是一种小蛋白（56个残基），结构稳定，为单结构域蛋白，是蛋白质折叠与设计领域中使用最为广泛的模型系统之一。最近，已确定了一种五元GB1核心突变体（L5V/A26F/F30V/Y33F/A34F）的核磁共振（NMR）结构和X射线结构，该突变体呈现出意想不到的、相互缠绕的四聚体结构。在此，我们报告另一种突变体的NMR结构，该突变体由上述四聚体突变体通过将单个氨基酸位置F26还原为野生型序列A26而获得。该结构揭示了一种结构域交换二聚体，涉及第二个β发夹的交换。由此产生的整体结构包含一个八链β折叠，其凹面被两个α螺旋覆盖。该二聚体以93（±10）μM的解离常数解离为部分折叠的单体形式。
