Kahana E, Marsh P J, Henry A J, Way M, Gratzer W B
Medical Research Council Muscle and Cell Motility Unit, King's College, London.
J Mol Biol. 1994 Jan 28;235(4):1271-7. doi: 10.1006/jmbi.1994.1080.
The presumptive rod domain of dystrophin contains a series of degenerate repeating sequences with homology to those of spectrin. To determine the relation of the implied structural repeating units to the sequence repeat (the phasing), recombinant fragments of the domain of dystrophin were prepared by expression in Escherichia coli. The phasing was established by identifying the minimum sequence element that would form a stable fold of high (approx. 75%) alpha-helicity: by contrast, incorrectly phased fragments had labile structure with an average alpha-helicity of about 40%. The isolated folded structural repeat showed high stability towards proteolysis and a urea-denaturation profile with a plateau at low denaturant concentration, indicative of a unique folded conformation. The phasing is consistent with a structure inferred from analysis of the amino acid sequence and also found in spectrin, in which each structural repeat comprises a three-stranded coiled-coil, made up of one short helix (approx. 30 residues) and the N and C-terminal halves of two separate long helices, such that each long helix participates in the formation of two contiguous structural units.
肌营养不良蛋白的推定杆状结构域包含一系列与血影蛋白的重复序列具有同源性的简并重复序列。为了确定隐含的结构重复单元与序列重复（相位）之间的关系，通过在大肠杆菌中表达制备了肌营养不良蛋白结构域的重组片段。通过鉴定能够形成高（约75%）α-螺旋度稳定折叠的最小序列元件来确定相位：相比之下，相位错误的片段结构不稳定，平均α-螺旋度约为40%。分离出的折叠结构重复对蛋白酶解具有高稳定性，并且在低变性剂浓度下具有平台期的尿素变性曲线，表明其具有独特的折叠构象。该相位与从氨基酸序列分析推断出的结构一致，并且在血影蛋白中也发现了这种结构，其中每个结构重复包含一个三链卷曲螺旋，由一个短螺旋（约30个残基）以及两个独立长螺旋的N端和C端一半组成，使得每个长螺旋参与形成两个相邻的结构单元。
