Protein Phase Separation during Stress Adaptation and Cellular Memory

Cells need to organise and regulate their biochemical processes both in space and time in order to adapt to their surrounding environment. Spatial organisation of cellular components is facilitated by a complex network of membrane bound organelles. Both the membrane composition and the intra-organellar content of these organelles can be specifically and temporally controlled by imposing gates, much like bouncers controlling entry into night-clubs. In addition, a new level of compartmentalisation has recently emerged as a fundamental principle of cellular organisation, the formation of membrane-less organelles. Many of these structures are dynamic, rapidly condensing or dissolving and are therefore ideally suited to be involved in emergency cellular adaptation to stresses. Remarkably, the same proteins have also the propensity to adopt self-perpetuating assemblies which properties fit the needs to encode cellular memory. Here, we review some of the principles of phase separation and the function of membrane-less organelles focusing particularly on their roles during stress response and cellular memory

Prion-like proteins as epigenetic devices of stress adaptation.

Epigenetic modifications allow cells to quickly alter their gene expression and adapt to different stresses. In addition to direct chromatin modifications, prion-like proteins have recently emerged as a system that can sense and adapt the cellular response to stressful conditions. Interestingly, such responses are maintained through prions' self-templating conformations and transmitted to the progeny of the cell that established a prion trait. Alternatively, mnemons are prion-like proteins which conformational switch encodes memories of past events and yet does not propagate to daughter cells. In this review, we explore the biology of the recently described prions found in Saccharomyces cerevisiae including [ESI+], [SMAUG+], [GAR+], [MOT3+], [MOD+], [LSB+] as well as the Whi3 mnemon. The reversibility of the phenotypes they encode allows cells to remove traits which are no longer adaptive under stress relief and chaperones play a fundamental role in all steps of prion-like proteins functions. Thus, the interplay between chaperones and prion-like proteins provides a framework to establish responses to challenging environments

Hydrolysis of plant biomass at different growth stages using enzyme cocktails for increased fermentable hydrolysates

In this experiment, optimum experimental conditions for the enzymatic hydrolysis of grass at different stages of growth were obtained by using the Taguchi methodology. Rye grass silage and three growth stages of Italian rye grass samples were used to determine optimum hydrolysis conditions. Five factors (pretreatment, enzyme composition, incubation temperature, pretreatment time, pH) influencing the hydrolysis process were studied at the individual and interactive levels. All selected experimental factors influenced the hydrolysis of grass. At the individual level, pretreatment of grass with NaOH and enzyme composition had the greatest influence (75% and 14.7% of the variance respectively) on enzymatic hydrolysis. Incubation temperature, pretreatment time and pH had influences of 8.1%, 2.2% and 0.055%, respectively. pH and incubation temperature had the most significant interaction effect (65.6%) on enzymatic hydrolysis. The factors with the least individual influence had the most significant interaction effect on enzymatic hydrolysis. Hydrolysis was improved when optimised conditions were applied to different growth stages of Italian rye grass