Biomolecular condensates are membraneless organelles that assemble through multivalent interactions among proteins and nucleic acids. They concentrate a subset of molecules within a dynamic microdomain, shaping processes such as transcription, RNA processing, and signaling. Condensate research has gained increasing attention in recent years due to several key advances including phase transition in the field. The biological relevance of biomolecular condensates has been associated with processes in development and disease, including neurodegeneration, cancer, and viral infection; however, their molecular composition and functional roles remain incompletely characterized.
Despite their functional importance, defining the true molecular composition of biomolecular condensates remains a major challenge. Many condensates are small, transient, and heterogeneous, often forming at submicron to micron scales and exhibiting rapid exchange of components with their surrounding environment. These properties complicate efforts to distinguish bona fide condensate residents from transiently associated or background molecules. Moreover, condensates frequently coexist with neighboring nuclear or cytoplasmic structures, making spatially precise isolation difficult and raising concerns about contamination when bulk biochemical approaches are applied.
Traditional purification strategies face additional limitations when applied to condensates. Biochemical fractionation or affinity-based enrichment such as proximity labeling often requires either genetic modification, chemical crosslinking, or prolonged processing, which can disrupt weak multivalent interactions or alter condensate composition. While mass spectrometry serves as a robust platform for unbiased discovery, the fidelity of the derived proteome is strictly limited by the specificity of the isolation strategy; sub-optimal purification inevitably confounds the dataset with non-specific interactors.
A closer look at PML nuclear bodies – a case study
Promyelocytic leukemia (PML) protein nuclear bodies (PML‑NBs) exemplify both the excitement and the frustration surrounding condensate research. PML-NBs are condensates organized by the PML protein. They are multifunctional hubs: regulating antiviral responses and fine-tuning p53 activity by recruiting modifiers that add or remove post‑translational modifications (PTMs). PML‑NBs are implicated in leukemia, neurodegeneration and viral infection, making them attractive drug targets.
Despite robust research efforts, we still do not know their complete molecular composition. PTM proteins are actively recruited to PML-NBs. SUMOylation, phosphorylation and acetylation of PML and other condensate-associated proteins dynamically regulate condensate protein recruitment1; altering these modifications changes which proteins enter the condensate. Existing purification strategies may perturb PTM, thus introducing composition changes.
Unraveling condensate proteomes and functions by microscopy-guided protein purification
Syncell’s Microscoop® platform is uniquely capable of unlocking the proteome of condensates. Instead of cell homogenization or relying on genetically encoded tags for proximity labeling, Microscoop uses microscopy‑guided photo‑biotinylation to label proteins only in a user‑defined region with a labeling precision down to 25 nm. The downstream pulldown effectively achieves spatial protein purification, which enables nanoscopic proteomics after mass spectrometry analysis. Key features include:
- High spatial precision. Down to 25-nm labeling precision which is smaller than all condensates. This allows selective sampling of individual nuclear bodies with almost no contamination from surrounding nucleoplasm, and allowing the interrogation of the interactome between known proteins and unknown proteins within the condensates.
- In situ proteomics. Because proteins are tagged directly in situ, no genetic modification or proximity enzyme fusion is required. The method works on fixed cells, fresh‑frozen tissue and FFPE samples.
- Unbiased discovery. Automated photolabeling of 1000s of condensates captures the majority of the localized protein composition, including transient or low‑abundance components, enabling the discovery of unexpected regulators. For example, researchers used Microscoop to profile nuclear Polycomb Repressive Complex 2 condensates in triple‑negative breast cancer (TNBC) cells and identified the PHF19 as a critical factor for condensate formation and metastasis in the TNBC cell model2.
By mapping the proteome of condensates with such precision, Microscoop could fill the current technological gap. In the context of PML‑NBs, Microscoop could be used to photolabel PM-NBs under different stress conditions or after perturbations of SUMOylation/phosphorylation. Mass‑spectrometric analysis would reveal which proteins enter or leave the condensate in each state, providing functional clues. Similarly, mapping the proteomes of Cajal bodies, P bodies, paraspeckles or super‑enhancer condensates across differentiation or disease states would help decode the roles of these bodies.
Outlook
The condensate field is shifting from descriptive imaging to mechanistic dissection. High‑throughput mass spectrometry and machine‑learning predictions have elucidated how many condensate proteins may remain unidentified3,4. Yet the biggest breakthroughs will likely come from the nanoscopic proteomic technology that can visualize and then sample condensates in their native environment.
By enabling precise, unbiased proteomic mapping at subcellular scales, Microscoop promises to transform our understanding of biomolecular condensates. Microscoop will help answer outstanding questions such as: Which proteins scaffold versus transiently visit a condensate? How do post‑translational modifications tune composition? Why do condensate proteomes change under stress or in disease? What proteins are on the boundaries of the specific condensates of interest? Answering these questions will not only advance fundamental biology but also reveal new therapeutic targets in cancer, neurodegeneration and infectious disease.
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