Intracellular compartmentation is a key strategy for the functioning of a cell. In 2010, several studies revealed that the metabolic enzyme CTP synthase (CTPS) can form filamentous structures termed cytoophidia in prokaryotic and eukaryotic cells. However, recent structural studies showed that CTPS only forms inactive product-bound filaments in bacteria while forming active substrate-bound filaments in eukaryotic cells. In this study, using negative staining and cryo-electron microscopy, we demonstrate that Drosophila CTPS, whether in substrate-bound or product-bound form, can form filaments. Our results challenge the previous model and indicate that substrate-bound and product-bound filaments can coexist in the same species. We speculate that the ability to switch between active and inactive cytoophidia in the same cells provides an additional layer of metabolic regulation.

细胞内分隔是细胞功能的关键策略。2010年，几项研究表明，代谢酶CTP合酶（CTPS）可以在原核和真核细胞中形成丝状结构，称为胞吞。然而，最近的结构研究表明，CTPS仅在细菌中形成与活性成分结合的细丝，而在真核细胞中形成与活性物质结合的细丝。在这项研究中，使用阴性染色和冷冻电子显微镜，我们证明了果蝇无论是基质结合形式还是产品结合形式，CTPS都可以形成细丝。我们的结果挑战了先前的模型，并表明与基质结合的细丝和与产品结合的细丝可以共存于同一物种中。我们推测，在相同细胞中有活性和无活性细胞吞噬之间切换的能力提供了新的代谢调节层。