Structural basis for Retriever-SNX17 assembly and endosomal sorting

Separation of powers: A key feature underlying the neuroprotective role of Retromer in age-related neurodegenerative disease?

The retromer complex was discovered in Saccharomyces cerevisiae as a multiprotein, pentameric assembly essential for recycling of integral membrane cargo proteins through the endosomal network [1,2]. We now understand how retromer is assembled, its membrane architecture, and how it selects proteins for recycling [3-6]. Conserved across eukaryotes, analyses have revealed retromer's role in organism development, and homeostasis and has linked retromer defects with age-related Alzheimer's disease and Parkinson's disease and other neurological disorders [3,5,7]. Indeed, stabilizing retromer function is now actively considered a therapeutic strategy [8]. Here, we reflect on its structural and functional evolution rather than overviewing retromer biology (see, e.g. [5,7]). Specifically, we clarify the organization of the human retromer to provide greater focus for future research, especially within the context of retromer's function in neuroprotection.

SNX17 knockdown improves post-ischemic angiogenesis via blocking lysosomal dependent VEGFR degradation

The treatment options for critical limb ischemia (CLI) are limited, and existing methods are often ineffective in restoring microvascular blood supply. We recently explored the association of sorting nexin 17 (SNX17) with angiogenesis. Knockdown of SNX17 promotes angiogenesis and increased blood flow in hindlimb from hindlimb ischemia mice, accompanied with a higher limb salvage rate. This phenomenon can be attributed to the critical role of SNX17 in the degradation of some angiogenic factor receptors, including vascular endothelial growth factor receptor (VEGFR). The linkage between VEGFR and SNX17 facilitates its trafficking to lysosomal degradation. In the absence of SNX17, VEGFR accumulates in early endosomes, leading to prolonged and intensified activation, and consequently promoting angiogenesis. The current study shows that SNX17 plays an important role in angiogenesis by regulating the stability of angiogenic factor receptors, such as VEGFR, and presents a new strategy for facilitating tissue repair in ischemic environments.

Identification of novel Kv1.3 channel-interacting proteins using proximity labelling in T-cells

Potassium channels regulate membrane potential, calcium flux, cellular activation and effector functions of adaptive and innate immune cells. The voltage-activated Kv1.3 channel is an important regulator of T cell-mediated autoimmunity and microglia-mediated neuroinflammation. Kv1.3 channels, via protein-protein interactions, are localized with key immune proteins and pathways, enabling functional coupling between K+ efflux and immune mechanisms. To gain insights into proteins and pathways that interact with Kv1.3 channels, we applied a proximity-labeling proteomics approach to characterize protein interactors of the Kv1.3 channel in activated T-cells. Biotin ligase TurboID was fused to either N or C termini of Kv1.3, stably expressed in Jurkat T cells and biotinylated proteins in proximity to Kv1.3 were enriched and quantified by mass spectrometry. We identified over 1,800 Kv1.3 interactors including known interactors (beta-integrins, Stat1) although majority were novel. We found that the N-terminus of Kv1.3 preferentially interacts with protein synthesis and protein trafficking machinery, while the C-terminus interacts with immune signaling and cell junction proteins. T-cell Kv1.3 interactors included 335 cell surface, T-cell receptor complex, mitochondrial, calcium and cytokine-mediated signaling pathway and lymphocyte migration proteins. 178 Kv1.3 interactors in T-cells also represent genetic risk factors of T cell-mediated autoimmunity, including STIM1, which was further validated using co-immunoprecipitation. Our studies reveal novel proteins and molecular pathways that interact with Kv1.3 channels in adaptive (T-cell) and innate immune (microglia), providing a foundation for how Kv1.3 channels may regulate immune mechanisms in autoimmune and neurological diseases.

Selective cargo and membrane recognition by SNX17 regulates its interaction with Retriever

The Retriever complex recycles a wide range of transmembrane proteins from endosomes to the plasma membrane. The cargo adapter protein SNX17 has been implicated in recruiting the Retriever complex to endosomal membranes, yet the details of this interaction have remained elusive. Through biophysical and structural model-guided mutagenesis studies with recombinant proteins and liposomes, we have gained a deeper understanding of this process. Here, we demonstrate a direct interaction between SNX17 and Retriever, specifically between the C-terminal region of SNX17 and the interface of the Retriever subunits VPS35L and VPS26C. This interaction is enhanced upon the binding of SNX17 to its cargo in solution, due to the disruption of an intramolecular autoinhibitory interaction between the C-terminal region of SNX17 and the cargo binding pocket. In addition, SNX17 binding to membranes containing phosphatidylinositol-3-phosphate also promotes Retriever recruitment in a cargo-independent manner. Therefore, this work provides evidence of the dual activation mechanisms by which SNX17 modulates Retriever recruitment to the proximity of cargo and membranes, offering significant insights into the regulatory mechanisms of protein recycling at endosomes.