The term “biomolecular condensates” is used to describe membraneless compartments in eukaryotic cells, accumulating proteins and nucleic acids. Biomolecular condensates are formed as a result of liquid–liquid phase separation (LLPS). Often, they demonstrate properties of liquid-like droplets or gel-like aggregates; however, some of them may appear to have a more complex structure and high-order organization. Membraneless microcompartments are involved in diverse processes both in cytoplasm and in nucleus, among them ribosome biogenesis, regulation of gene expression, cell signaling, and stress response. Condensates properties and structure could be highly dynamic and are affected by various internal and external factors, e.g., concentration and interactions of components, solution temperature, pH, osmolarity, etc. In this review, we discuss variety of biomolecular condensates and their functions in live cells, describe their structure variants, highlight domain and primary sequence organization of the constituent proteins and nucleic acids. Finally, we describe current advances in methods that characterize structure, properties, morphology, and dynamics of biomolecular condensates in vitro and in vivo.

Numerous studies have demonstrated that people with type 2 diabetes mellitus (associated with IAPP peptide aggregation) show an increased incidence of Alzheimer’s disease (associated with Aβ aggregation), but the mechanism responsible for this correlation is presently unknown. Here, we applied a yeast-based model to study the interactions of IAPP with PrP (associated with TSEs) and with the Aβ42 peptide. We demonstrated that fluorescently tagged IAPP forms detergent-resistant aggregates in yeast cells. Using the FRET approach, we showed that IAPP and Aβ aggregates co-localize and physically interact in yeast cells. We also showed that this interaction is specific and that there is no interaction between IAPP and PrP in the yeast system. Our data confirmed a direct physical interaction between IAPP and Aβ42 aggregates in a living cell. Based on these findings, we hypothesize that this interaction may play a crucial role in seeding Aβ42 aggregation in T2DM patients, thereby promoting the development of AD.

Amyloid protein aggregation is a key factor in the development of a variety of serious diseases in humans, commonly named as amyloidoses (Alzheimer’s and Parkinson’s diseases, type II diabetes, etc.), and a determinant of protein-based inheritance in lower eukaryotes. In yeast, translation termination factor Sup35 is one of the most extensively studied amyloidogenic proteins. Aggregation of Sup35 (induction of [PSI⁺] prion) decreases its functional activity and leads to the suppression of nonsense-mutation as stop-codons become recognized as meaningful more frequently. This phenomenon is the basis of phenotypic detection of Sup35 aggregation in yeast strains possessing nonsense mutation ade1-14 in ADE1 gene. Yeast is convenient model for genetic, biochemical and molecular biology studies. Yeast genome can be easily edited and plasmids can be used for induction of gene expression. Yeast is suitable for analysis of mammalian genes and proteins and thus can be applied for the analysis of amyloidogenic properties of proteins associated with human diseases. Phenotyping detection of [PSI⁺] prion can be modified for the analysis of amyloid aggregation of mammalian proteins in yeast. We use genetically modified yeasts Saccharomyces cerevisiae adopted for amyloid biology research. The mutations leading to auxotrophy toward certain amino acids (leucine, lysine, tryptophane, histidine) and nucleobases (adenine, uracil) were implemented into yeast genome allowing phenotyping detection of [PSI⁺] and the usage of plasmids for the investigation of mammalian protein in yeast. Application of yeast-based experimental system for studies of different aspects of human amyloidoses is discussed. This study was supported by Saint Petersburg State University (project 93025998).

Protein intrinsically disordered regions (IDRs) play important biological roles despite lacking stable structures. IDRs drive the formation of both biomolecular condensates via liquid–liquid phase separation (LLPS) and solid fibrous amyloid aggregates. Amyloids can be pathogenic and may exhibit self-perpetuating (prion) properties. Relationships between LLPS and the amyloid-forming and prion-propagating abilities of IDRs remain poorly understood. The N-proximal IDR of the yeast translation termination factor eRF3 (Sup35) can form both liquid condensates and heritable amyloid-based prions and serves as a powerful model for investigating these phenomena due to the availability of simple phenotypic, cytological and biochemical assays. Deletion analysis demonstrates that the N-proximal prion domain (Sup35N) of Sup35 is sufficient for chaperone-dependent prion propagation and that various regions of this domain show differential impacts on LLPS, amyloid aggregation, and prion inheritance. Specifically, the N-terminal NQ-rich stretch and the region of oligopeptide repeats are the most important contributors to the LLPS and formation of amyloid fibrils, while oligopeptide repeats and the C-terminal region of Sup35N are crucial for prion inheritance. Contrary to previous reports, the NQ-rich stretch is not required for prion formation and inheritance in yeast. Our data indicate that, in addition to amino acid composition, specific sequence motifs control reversible and heritable assemblies of Sup35.