Background

TRIM (Tripartite Motif) proteins are a large family of E3 ubiquitin ligases involved in immunity, development, intracellular signaling, and disease. They share a conserved modular architecture containing a RING domain, B-box(es), coiled-coil (CC) domain, and variable C-terminal domains. Although a few TRIM proteins were previously known to form puncta or subcellular bodies, it was unclear whether biomolecular condensation is a general property of the TRIM family or only limited to specific members.

Biomolecular condensates are membrane-less compartments formed through multivalent interactions that concentrate proteins and regulate biochemical reactions. Such condensates can modulate enzymatic activity, organize cytoskeletal structures, and control signaling pathways. Since TRIM proteins naturally oligomerize and contain interaction domains, the authors hypothesized that condensation may be a widespread and functionally important mechanism governing TRIM protein behavior. 

Scientific Question

The central question of this study was whether condensation is a common and fundamental feature of human TRIM proteins. Specifically, the authors asked: do most TRIM proteins form condensates, what structural domains drive this process, and how does condensation influence TRIM enzymatic activity and biological functions?

They also explored whether different TRIM proteins selectively co-condense with one another, whether disease-associated mutations disrupt condensation, and whether TRIM condensates participate in cellular processes such as cilia assembly and microtubule regulation. In essence, the study aimed to build a global framework linking TRIM protein structure, condensation behavior, and functional specificity. 

Main Findings

The authors systematically analyzed 75 human TRIM proteins and found that the majority (~75%) form condensate-like structures, including cytoplasmic puncta, nuclear puncta, centrosome-associated bodies, or fibrillar assemblies. This indicates that condensation is not an exception but a widespread property of the TRIM family. Many condensates displayed hallmark liquid-like behaviors such as fusion and fluorescence recovery after photobleaching (FRAP).

Mechanistically, the coiled-coil (CC) domain was identified as the key driver of condensation. Deleting the CC domain abolished condensate formation, while the CC domain alone was often sufficient to induce condensation. Importantly, disease-associated mutations within the CC domain disrupted condensate formation, suggesting that defective condensation may contribute to human pathologies, including cancer and genetic disorders.

Functionally, TRIM condensation modulated E3 ubiquitin ligase activity in a context-dependent manner. In some TRIM proteins, condensation enhanced ubiquitination activity, while in others it suppressed activity or had no effect. Beyond enzymatic control, certain TRIM condensates inhibited ciliogenesis by disrupting centriolar satellites, whereas another subgroup stabilized microtubules. The study also revealed selective co-condensation between specific TRIM pairs, demonstrating that homologous proteins can form highly specific interaction networks rather than mixing randomly.

Key Methods Used

The authors first generated a library of fluorescently tagged human TRIM proteins and expressed them in mammalian cells to systematically examine subcellular localization. Live-cell imaging, confocal microscopy, and FRAP were used to determine whether TRIM puncta behaved as dynamic condensates. Endogenous knock-in cell lines were also created for selected TRIM proteins to validate physiological condensate formation.

To define structural requirements, the study employed domain deletion mutants, point mutations, and domain-swapping experiments, particularly focusing on the coiled-coil domain. Protein-protein interactions were tested by immunoprecipitation, and ubiquitination activity was measured using auto-ubiquitination assays and a proximity-based biotinylated ubiquitination system (BioE3). These approaches allowed direct comparison of wild-type versus condensation-defective mutants.

For functional characterization, the authors performed TurboID proximity-labeling mass spectrometry to identify proteins enriched in TRIM condensates. They then used cell-based assays to evaluate effects on centriolar satellites, cilia formation, and microtubule stability using markers such as PCM1, ARL13B, and α-tubulin. Together, these methods provided a comprehensive structural, biochemical, and functional map of TRIM protein condensation. 

Research articel link: Coiled-coil-domain-mediated TRIM E3 protein condensation modulates enzymatic activity and functional specificity: Cell Reports

转载本文请联系原作者获取授权，同时请注明本文来自陈建雄科学网博客。
链接地址：https://blog.sciencenet.cn/blog-3545398-1531614.html

上一篇：液体中分子的结合记忆
下一篇：抑制RNAj聚合酶I活性导致染色质修饰改变