In response to osmotic stress, proline is accumulated in many bacterial and plant cells as an osmoprotectant. The yeast Saccharomyces cerevisiae induces trehalose or glycerol synthesis but does not increase intracellular proline levels during various stresses. Using a proline-accumulating mutant, we previously found that proline protects yeast cells from damage by freezing, oxidative, or ethanol stress. This mutant was recently shown to carry an allele of PRO1 which encodes the Asp154Asn mutant gamma-glutamyl kinase (GK), the first enzyme of the proline biosynthetic pathway. Here, enzymatic analysis of recombinant proteins revealed that the GK activity of S. cerevisiae is subject to feedback inhibition by proline. The Asp154Asn mutant was less sensitive to feedback inhibition than wild-type GK, leading to proline accumulation. To improve the enzymatic properties of GK, PCR random mutagenesis in PRO1 was employed. The mutagenized plasmid library was introduced into an S. cerevisiae non-proline-utilizing strain, and proline-overproducing mutants were selected on minimal medium containing the toxic proline analogue azetidine-2-carboxylic acid. We successfully isolated several mutant GKs that, due to extreme desensitization to inhibition, enhanced the ability to synthesize proline better than the Asp154Asn mutant. The amino acid changes were localized at the region between positions 142 and 154, probably on the molecular surface, suggesting that this region is involved in allosteric regulation. Furthermore, we found that yeast cells expressing Ile150Thr and Asn142Asp/Ile166Val mutant GKs were more tolerant to freezing stress than cells expressing the Asp154Asn mutant.
Increase the total number of rows showing on this page using the pull-down located below the table, or use the page scroll at the table's top right to browse through the table's pages; use the arrows to the right of a column header to sort by that column; filter the table using the "Filter" box at the top of the table; click on the small "i" buttons located within a cell for an annotation to view further details.
| Gene | Phenotype | Experiment Type | Mutant Information | Strain Background | Chemical | Details |
|---|---|---|---|---|---|---|
| PRO1 | chemical compound accumulation: increased | classical genetics | activation Allele: pro1-D154N D154N (G460A); kinase domain mutated; increased catalytic activity; feedback inhibition insensitive | S288C | L-proline | |
| PRO1 | chemical compound accumulation: increased | classical genetics | activation Allele: pro1-E149K E149K (G445A); kinase domain mutated; feedback inhibition insensitive | S288C | L-proline | |
| PRO1 | chemical compound accumulation: increased | classical genetics | activation Allele: pro1-H306R H306R (A917G); junction between kinase and PUA domains mutated | S288C | L-proline | |
| PRO1 | chemical compound accumulation: increased | classical genetics | activation Allele: pro1-N142D,I166V N142D, I166V (A424G, A496G); kinase domain mutated; feedback inhibition insensitive | S288C | L-proline | |
| PRO1 | chemical compound accumulation: increased | classical genetics | activation Allele: PRO1-I150T I150T (T449C); variant located in the kinase domain between the allosteric and substrate binding sites; may increase substrate affinity; feedback inhibition insensitive | S288C | L-proline | |
| PRO1 | chemical compound accumulation: increased | classical genetics | activation Allele: pro1-S146P S146P (T436C); kinase domain mutated | S288C | L-proline | |
| PRO1 | chemical compound accumulation: increased | classical genetics | activation Allele: pro1-A105V A105V (C314T); kinase domain mutated | S288C | L-proline | |
| PRO1 | chemical compound accumulation: increased | classical genetics | activation Allele: pro1-N309D,R428C N309D, R428C (A925G, C1282T); junction between kinase and PUA domain, as well as the PUA domain mutated | S288C | L-proline | |
| PRO1 | chemical compound accumulation: increased | classical genetics | activation Allele: pro1-R148G,Q351R R148G, Q351R (A442G, A1052G); kinase and PUA domains mutated | S288C | L-proline | |
| PRO1 | chemical compound accumulation: increased | classical genetics | activation Allele: pro1-R148G R148G (A442G); kinase domain mutated | S288C | L-proline |