Protein Signaling Domains Laboratory, Department of Biological Sciences, Fralin Life Sciences Institute, and Center for Soft Matter and Biological Physics, Virginia Tech, Blacksburg, VA 24061, USA.
Research and Informatics, University Libraries, Biochemistry Department, and Center for Drug Discovery, Virginia Tech, Blacksburg, VA 24061, USA.
Structure. 2024 Oct 3;32(10):1677-1690.e5. doi: 10.1016/j.str.2024.08.003. Epub 2024 Aug 28.
Target of Myb1 (TOM1) facilitates the transport of endosomal ubiquitinated proteins destined for lysosomal degradation; however, the mechanisms regulating TOM1 during this process remain unknown. Here, we identified an adjacent DXXLL motif-containing region to the TOM1 VHS domain, which enhances its affinity for ubiquitin and can be modulated by phosphorylation. TOM1 is an endosomal phosphatidylinositol 5-phosphate (PtdIns5P) effector under Shigella flexneri infection. We pinpointed a consensus PtdIns5P-binding motif in the VHS domain. We show that PtdIns5P binding by TOM1 is pH-dependent, similarly observed in its binding partner TOLLIP. Under acidic conditions, TOM1 retained its complex formation with TOLLIP, but was unable to bind ubiquitin. S. flexneri infection inhibits pH-dependent endosomal maturation, leading to reduced protein degradation. We propose a model wherein pumping of H to the cytosolic side of endosomes contributes to the accumulation of TOM1, and possibly TOLLIP, at these sites, thereby promoting PtdIns5P- and pH-dependent signaling, facilitating bacterial survival.
TOM1（Myb1 靶蛋白 1）的作用是促进内体泛素化蛋白向溶酶体降解的运输；然而，在这个过程中调节 TOM1 的机制仍不清楚。在这里，我们确定了 TOM1 VHS 结构域附近的一个含有 DXXLL 基序的区域，该区域增强了其与泛素的亲和力，并可以通过磷酸化进行调节。TOM1 是 Shigella flexneri 感染时内体磷脂酰肌醇 5-磷酸（PtdIns5P）的效应物。我们在 VHS 结构域中确定了一个保守的 PtdIns5P 结合基序。我们表明，TOM1 与 PtdIns5P 的结合具有 pH 依赖性，在其结合伙伴 TOLLIP 中也观察到了这种依赖性。在酸性条件下，TOM1 保留了与 TOLLIP 的复合物形成，但无法结合泛素。S. flexneri 感染抑制 pH 依赖性内体成熟，导致蛋白降解减少。我们提出了一个模型，其中 H 泵到内体的胞质侧有助于 TOM1 和可能的 TOLLIP 在这些部位的积累，从而促进 PtdIns5P 和 pH 依赖性信号转导，促进细菌存活。
