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Researchers developed a method to push protein expression to extreme levels in yeast cells and found that nearly all tested proteins become toxic when sufficiently overexpressed, though the tolerable abundance varies widely between proteins. They created a metric called IE50 to quantify overexpression tolerance and discovered that tolerance correlates with protein structural order, cytoplasmic localization, and low sulfur content. At very high abundance levels, some proteins triggered dramatic changes in cellular organization and formed large-scale intracellular structures through specific sequence regions.
Why it matters
This work challenges the binary classification of proteins as simply toxic or non-toxic, showing instead that toxicity is a quantitative property dependent on abundance. The findings have implications for understanding cellular protein homeostasis, synthetic biology applications where protein overexpression is used, and diseases involving protein aggregation or mislocalization.
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⚠️ Preprint – Noch nicht peer-reviewed
Dieser Artikel wurde noch nicht von unabhängigen Experten begutachtet. Die Ergebnisse sind vorläufig und sollten mit Vorsicht interpretiert werden.
Proteins are often classified as toxic or non-toxic without measuring the abundance reached, leaving constraints on tolerable protein abundance unresolved. We established a limit-pushing approach in Saccharomyces cerevisiae combining strong inducible expression with gTOW-mediated high-copy selection to counteract copy-number compensation while measuring protein abundance and growth. Nearly all of approximately 80 chromosome I proteins severely inhibited growth or reduced viability at sufficiently high abundance. We established IE50, the expression level associated with a 50% reduction in growth rate, to quantify their widely varying overexpression tolerance. IE50 was positively associated with predicted structural order and cytoplasmic localization propensity and negatively associated with sulphur content. Single-cell imaging linked higher tolerance to proteins remaining cytoplasmic without becoming aggregation-positive and revealed abundance-dependent changes in localization and organelle morphology. At extreme abundance, Fun12, Nup60, and Pex22 generated distinct large-scale intracellular states through specific sequence regions. These findings establish overexpression toxicity as a quantitative property linked to protein characteristics and reveal both constraints on tolerable abundance and sequence-dependent capacities for intracellular organization.
Source: Limit-pushing overexpression reveals constraints on protein abundance