Phase separation has long been observed within aqueous mixtures of two or more different compounds such as proteins, salts, polysaccharides and synthetic polymers. A growing body of experimental evidence indicates that phase separation also takes place inside living cells, where intrinsically disordered proteins and other molecules such as RNA are thought to assemble into membraneless organelles. These structures represent a new paradigm of intracellular organisation and compartmentalisation in which biochemical processes can be coordinated in space and time. Two thermodynamic driving forces have been proposed for phase separation: the strengths of macromolecule-macromolecule and macromolecule-H2O interactions, and the perturbation of H2O structure about different macromolecules. In this Perspective, we propose that both driving forces act in a concerted manner to promote phase separation, which we describe in the context of the well-known structural dynamics of intrinsically disordered proteins in the cellular milieu. We further suggest that this effect can be extended to explain how the partial unfolding of globular proteins can lead to intracellular phase separation.

Stress granules (SGs) are among the most studied membraneless organelles that form upon heat stress (HS) to sequester unfolded, misfolded, or aggregated protein, supporting protein quality control (PQC) clearance. The folding states that are primarily associated with SGs, as well as the function of the phase separated environment in adjusting the energy landscapes, remain unknown. Here, we investigate the association of superoxide dismutase 1 (SOD1) proteins with different folding stabilities and aggregation propensities with condensates in cells, in vitro and by simulation. We find that irrespective of aggregation the folding stability determines the association of SOD1 with SGs in cells. In vitro and in silico experiments however suggest that the increased flexibility of the unfolded state constitutes only a minor driving force to associate with the dynamic biomolecular network of the condensate. Specific protein–protein interactions in the cytoplasm in comparison to SGs determine the partitioning of folding states between the respective phases during HS.

The marginal stability of globular proteins in the cell is determined by the balance between excluded volume effect and soft interactions. Quinary interactions are a type of soft interactions involved in intracellular organisation and known to have stabilising or destabilising effects on globular proteins. Recent studies suggest that globular proteins have structural flexibility, exhibiting more than one functional state. Here, we propose that the quinary-induced destabilisation can be sufficient to produce functional partially unfolded states of globular proteins. The biological relevance of this mechanism is explored, involving intracellular phase separation and regulatory stress response mechanisms.

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Background  Colorectal cancer is one of the most common types of cancer and is associated with a high lethality rate. Treatment is multidisciplinary, and neoadjuvant chemoradiation is recommended in locally advanced rectal cancer. About 15% of patients answer favorably to neoadjuvant chemoradiation, so it is important to determine the predictors of response. Objective  To review the results of studies that analyzes the predictors of complete pathological response to neoadjuvant chemoradiation in patients with locally advanced rectal cancer. Search methods  We searched for eligible articles in data bases Pubmed and Scopus, between the 12th and the 20th of March 2020. The following key words were used: “predictors of response”, “chemoradiation” and "locally advanced rectal cancer”. Selection criteria  Inclusion criteria: Studies including patients with locally advanced rectal cancer, patients receiving neoadjuvant chemoradiation as treatment, studies including predictors of response to neodjuvant chemoradiation, overall survival as an outcome and regarding language restrictions, only articles in English were accepted, only studies published until the 31st of December 2019 were accepted. Main results  Fourteen studies fulfilled the inclusion criteria. Thirteen are cohort studies and one is a clinical trial. Four groups of predictors were defined: blood markers, tumors, histopathological and patients’ characteristics. Author's conclusions  During the analysis of the articles, there were several predictors identified as potential candidates for clinical practice, such as high pre neoadjuvant chemoradiation Carcinoembryonic Antigen levels and small post neoadjuvant chemoradiation tumor size. Nevertheless, it is difficult to make definitive conclusions about the most reliable predictors. That is why it is crucial to initiate further studies with standardized cut-off values and a methodology homogenization.

The interpretation of salt´s effects on protein stability discriminates between low concentration regimes, dominated by ion specific-binding or Debye-Hückel screening, and high concentration regimes, generally described by Hofmeister effects. However,...