Biotechnology Terms Starting With Y
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Yeast Display
/ YEEST dih-SPLAY / · From Old English gist, meaning ferment or foam, and Latin displicare, meaning to unfold or exhibit.
Yeast Display is a molecular technique that presents proteins or peptides on the outer surface of yeast cells for high-throughput screening and directed evolution experiments.
Yeast display uses Saccharomyces cerevisiae to express target proteins fused to cell wall or membrane anchor proteins, typically Aga2p or Flo1p, positioning the protein of interest on the extracellular face of the cell. Libraries containing up to 10^9 sequence variants can be screened by fluorescence-activated cell sorting, allowing researchers to identify proteins with desired binding affinities or enzymatic properties in a single experiment. Unlike phage display, yeast display provides authentic eukaryotic post-translational modifications including glycosylation and disulfide bond formation, making it particularly valuable for developing therapeutic antibodies and studying protein-protein interactions.
Each sorted yeast cell retains the gene encoding its displayed protein, so successive rounds of sorting progressively enrich for variants with the target property while preserving the sequence information needed for downstream analysis. The platform has produced antibodies with picomolar affinities and enzyme variants with substantially enhanced catalytic efficiency compared to their natural starting sequences.
Yeast display contributed to the development of dupilumab, a monoclonal antibody approved for atopic dermatitis that generated over 10 billion dollars in annual sales by 2022, illustrating how directed evolution in yeast can yield blockbuster therapeutics. The platform can simultaneously display two different proteins on the same yeast cell, enabling direct measurement of heterodimeric binding interactions in a single screening step.
Yeast display is a slower, less powerful alternative to phage display. Yeast display uniquely provides eukaryotic folding and glycosylation machinery that produces proteins far more similar to their mammalian counterparts, giving it a distinct advantage for engineering antibodies and other therapeutic proteins that require proper post-translational modification.
Researchers at Stanford University used yeast display to evolve high-affinity nanobodies against the SARS-CoV-2 spike protein, screening over 100 million variants in Saccharomyces cerevisiae and identifying neutralizing candidates with binding affinities below 1 nanomolar. The entire selection process, from library construction to confirmed neutralizing hits, was completed within weeks, demonstrating the speed advantage of fluorescence-activated cell sorting over colony-based screening methods.
Yeast Expression System
/ YEEST ek-SPRESH-un SIS-tem / · From Old English gist, meaning ferment, Latin exprimere, meaning to press out, and Greek systema, meaning organized whole.
Yeast Expression System is a biotechnology platform using yeast cells, primarily Saccharomyces cerevisiae or Pichia pastoris, to produce recombinant proteins for research, industrial, and therapeutic applications.
Yeast expression systems combine the ease of microbial manipulation with eukaryotic post-translational modification capabilities, making them well suited for producing complex proteins that bacteria cannot fold or process correctly. Saccharomyces cerevisiae carries GRAS status from the FDA, making it preferred for food and pharmaceutical applications, while Pichia pastoris achieves higher protein yields, often exceeding 10 grams per liter in fermentation cultures. Both systems use strong inducible promoters, such as GAL1 in S.
cerevisiae or AOX1 in P. pastoris, to drive recombinant gene expression and can perform glycosylation, disulfide bond formation, and proteolytic processing.
Pichia pastoris can secrete recombinant proteins directly into the culture medium at concentrations exceeding 30 grams per liter, roughly 100-fold higher than typical mammalian cell systems. The alcohol oxidase 1 promoter driving this secretion is among the strongest characterized in any expression host, capable of accumulating the target protein to over 30 percent of total cellular protein under methanol induction.
Yeast cannot properly glycosylate human proteins. Engineered strains with humanized glycosylation pathways, developed by companies including Merck and Oxyrane, now produce therapeutic proteins carrying human-compatible glycan structures, eliminating the immunogenicity concerns associated with yeast-type high-mannose glycosylation.
Sanofi uses genetically modified Saccharomyces cerevisiae in industrial bioreactors to produce artemisinic acid, a precursor to the antimalarial drug artemisinin, yielding over 25 grams per liter and providing a consistent, affordable supply of the compound for malaria treatment in low-income countries. This fermentation-based route replaced a multi-step plant extraction process that depended on variable harvests of sweet wormwood (Artemisia annua) and could not reliably meet global demand.
Yeast Two-Hybrid System
/ YEEST TOO HY-brid SIS-tem / · Old English gist; Old English twa; Latin hybrida; Greek systema
Yeast Two-Hybrid System is a genetic assay that detects physical interactions between two proteins by reconstituting a split transcriptional activator inside yeast cells, triggering reporter gene expression only when the proteins of interest bind each other.
Stanley Fields and Ok-kyu Song developed the system in 1989 by splitting a transcriptional activator into a DNA-binding domain fused to one protein of interest and an activation domain fused to a second; when the two proteins interact, the halves come together and switch on a reporter gene such as lacZ or HIS3. Genome-scale yeast two-hybrid screens have mapped protein interaction networks for organisms including budding yeast (Saccharomyces cerevisiae), the roundworm Caenorhabditis elegans, fruit fly (Drosophila melanogaster), and humans, producing interactome maps containing tens of thousands of binary interactions. Each screen can test millions of pairwise combinations by transforming a bait plasmid and a prey library simultaneously into yeast and selecting colonies that activate the reporter.
Known limitations include false positives generated by sticky or auto-activating proteins, false negatives from proteins that misfold or require non-yeast post-translational modifications, and an inability to detect interactions that depend on membrane embedding. Hits from yeast two-hybrid screens are routinely validated by co-immunoprecipitation, bimolecular fluorescence complementation, or surface plasmon resonance before being accepted as biologically meaningful interactions.
A 2011 genome-scale yeast two-hybrid screen of the human proteome, published by Vidal and colleagues, identified approximately 14,000 binary protein-protein interactions, most of which had no prior experimental support, expanding the known human interactome by an order of magnitude. That dataset has since guided drug target identification for diseases ranging from cancer to neurodegeneration.
Yeast →A positive result in the yeast two-hybrid system proves that two proteins interact in their native cellular environment. The assay reports an interaction under yeast nuclear conditions, and the result requires confirmation in the organism and cell type where the proteins naturally reside.
Researchers used yeast two-hybrid screening to identify proteins that bind the Huntingtin protein, which carries an abnormally expanded polyglutamine tract in Huntington's disease patients. Screens performed in S. cerevisiae identified more than 15 interacting partners, several of which are now being investigated as therapeutic targets to interrupt the toxic protein network driving neurodegeneration.