Department of Biomedical Sciences, Florida State University, Tallahassee, Florida, USA.
Protein Sci. 2020 Jul;29(7):1629-1640. doi: 10.1002/pro.3877. Epub 2020 May 25.
Gene duplication and fusion events in protein evolution are postulated to be responsible for the common protein folds exhibiting internal rotational symmetry. Such evolutionary processes can also potentially yield regions of repetitive primary structure. Repetitive primary structure offers the potential for alternative definitions of critical regions, such as the folding nucleus (FN). In principle, more than one instance of the FN potentially enables an alternative folding pathway in the face of a subsequent deleterious mutation. We describe the targeted mutation of the carboxyl-terminal region of the (internally located) FN of the de novo designed purely-symmetric β-trefoil protein Symfoil-4P. This mutation involves wholesale replacement of a repeating trefoil-fold motif with a "blade" motif from a β-propeller protein, and postulated to trap that region of the Symfoil-4P FN in a nonproductive folding intermediate. The resulting protein (termed "Bladefoil") is shown to be cooperatively folding, but as a trimeric oligomer. The results illustrate how symmetric protein architectures have potentially diverse folding alternatives available to them, including oligomerization, when preferred pathways are perturbed.
基因复制和融合事件被认为是导致具有内部旋转对称性的常见蛋白质折叠的原因。这种进化过程也可能产生重复的一级结构区域。重复的一级结构为关键区域（如折叠核）提供了替代定义的可能性。原则上，面对随后的有害突变，FN 的一个以上实例有可能实现替代的折叠途径。我们描述了从头设计的纯对称β三叶状蛋白 Symfoil-4P 中（内部定位的）FN 的羧基末端区域的靶向突变。该突变涉及用来自β-螺旋桨蛋白的“叶片”基序整体替换重复的三叶折叠基序，并假设该 Symfoil-4P FN 区域被捕获在非生产性折叠中间物中。所得蛋白质（称为“Bladefoil”）被证明是协同折叠的，但作为三聚体寡聚物。结果表明，对称蛋白质结构具有潜在的多样化折叠选择，包括寡聚化，当首选途径受到干扰时。
