Prions are self-perpetuating, alternative protein conformations associated with neurological diseases and normal cellular functions. Saccharomyces cerevisiae contains many endogenous prions – providing a powerful system to study prionization. Previously, we demonstrated that Swi1, a component of the SWI/SNF chromatin-remodeling complex, can form the prion [SWI⁺]. A small region, Swi1_1-38, with a unique amino-acid composition of low complexity, acts as a prion domain and supports [SWI⁺] propagation. Here, we further examine Swi1_1-38 through site-directed mutagenesis. We found that mutations of the two phenylalanine residues or threonine tract inhibit Swi1_1-38 aggregation. In addition, mutating both phenylalanines can abolish de novo prion formation by Swi1_1-38 whereas mutating only one phenylalanine does not. Replacement of half or the entire eight-threonine tract with alanines has the same effect, possibly disrupting a core region of Swi1_1-38 aggregates. We also show that Swi1_1-38 and its prion-fold-maintaining mutants form high-molecular-weight, SDS-resistant aggregates whereas the double phenylalanine mutants eliminate these protein species. These results indicate the necessity of the large hydrophobic residues and threonine tract in Swi1_1-38 in prionogenesis – possibly acting as important aggregatable regions. Our findings thus highlight the importance of specific amino-acid residues in the Swi1 prion domain in prion formation and maintenance.

中文翻译：

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定义朊病毒形成和维持中 Swi1 朊病毒结构域的关键残基

朊病毒是与神经系统疾病和正常细胞功能相关的自我延续的替代蛋白质构象。Saccharomyces cerevisiae含有许多内源性朊病毒——提供了一个强大的系统来研究朊病毒化。以前，我们证明了 SWI/SNF 染色质重塑复合物的组成部分 Swi1 可以形成朊病毒 [ SWI ⁺ ]。一个小区域 Swi1 _1-38具有独特的低复杂性氨基酸组成，充当朊病毒域并支持 [ SWI ⁺ ] 传播。在这里，我们通过定点诱变进一步检查 Swi1 _1-38。我们发现两个苯丙氨酸残基或苏氨酸束的突变抑制 Swi1 _1-38聚合。此外，突变两种苯丙氨酸可以消除Swi1 _1-38从头形成朊病毒，而仅突变一种苯丙氨酸则不会。用丙氨酸替换一半或整个八苏氨酸束具有相同的效果，可能会破坏 Swi1 _1-38聚集体的核心区域。我们还表明 Swi1 _1-38及其保持朊病毒折叠的突变体形成高分子量、抗 SDS 的聚集体，而双苯丙氨酸突变体消除了这些蛋白质种类。这些结果表明 Swi1 _{1-38 中}大疏水残基和苏氨酸束的必要性在 prionogenesis 中——可能充当重要的可聚集区域。因此，我们的研究结果强调了 Swi1 朊病毒结构域中特定氨基酸残基在朊病毒形成和维持中的重要性。