Abstract
Engineering synthetic intrinsically disordered proteins (synIDPs) enables regulation of biomolecular condensation and protein solubility. However, limited understanding of how sequence-dependent interaction cooperativity relates to the fitness impacts of synIDPs on endogenous cellular processes constrains our design capability. Here, to circumvent this design challenge, we present a systematic directed evolution method for the evolution of synIDPs capable of mediating diverse phase behaviors in living cells. The selection methods allow us to evolve a toolbox of synIDPs with distinct phase behaviors and thermoresponsive features in living cells, leading to the evolution of synthetic condensates. The reverse-selection method further allows us to select synIDPs as solubility tags. We demonstrate the applications of the evolved synIDPs in protein circuits to (1) regulate intracellular protein activity and (2) reverse antibiotic resistance. Our systematic evolution and selection strategies provide a versatile platform for developing synIDPs for broad applications in synthetic biology and biotechnology.

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Acknowledgements
Y.D. acknowledges the experimental and funding support from the Center for Biomolecular Condensates and the McKelvey School of Engineering at Washington University. We acknowledge the experimental and material support and discussion with J. Su of the A. Chilkoti Lab at Duke University.
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Y.D. conceptualized the study and acquired funding. Y.D. and Y.M. designed the experiments. Y.M., L.Y., Y.C., M.W.C. and W.Y. performed the evolution experiments. L.Y. performed the computational algorithm analysis. Y.M., Y.C. and W.Y. purified the proteins. Y.M. and L.Y. performed the synthetic biology experiments. Y.M., L.Y. and M.W.C. analyzed the data. Y.D. supervised the work. Y.D. and Y.M. wrote the manuscript. All authors read and/or edited the manuscript.
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Y.D. and Y.M. are coinventors on a US provisional patent application (application number: 63/884,618) that incorporates the methods described in this paper. Their interests are reviewed and managed by Washington University in St. Louis in accordance with their conflict-of-interest policies. The remaining authors declare no competing interests.
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Extended data
Extended Data Fig. 1 Verification of genetic elements for the development of selection methods for directed evolution of synIDPs.
a, Evaluation of the killing efficiency of toxic proteins using plate-based assay. Data is represented as mean ± SD. n = 3 biological replicates. b, Evaluation of the killing efficiency of protein E against different strains using plate-based assay. Data is represented as mean ± SD. n = 3 biological replicates. c, Representative images of the growth conditions (based on turbidity) for cells expressing protein E-RLPWT and protein E alone. Time points correspond to durations after induction. d, Confocal images of cells expressing Protein E-RLPWT at different time points after dyeing with mixture of SYTO 9 and propidium iodide (PI). When used alone, the SYTO 9 stain generally labels all bacteria in a population. In contrast, PI penetrates only bacteria with damaged membranes, causing a reduction in the SYTO 9 stain fluorescence when both dyes are present. The arrows mark the positions of the biomolecular condensates in the cell. Scale bar represents 5 µm. e, Evaluation of the fraction of live DH5α cells expressing Protein E–RLPWT at different time points post-induction, measured using a plate reader. Data is represented as mean ± SD. n = 3 biological replicates. f, SDS-PAGE analysis of whole-cell lysates. Whole-cell lysates were analyzed by SDS-PAGE to evaluate the expression level of protein E and protein E-RLP (MW: 27.6 kDa). The results showed that protein E-RLP was expressed at substantially higher levels than protein E, which confirmed that the restored cell survival was not due to differences in protein expression levels. The arrows mark the positions of the target proteins on the bands.
Extended Data Fig. 2 Verification of selection methods for the directed evolution of synIDPs.
a, Design principle to transform a soluble promoting residue into a hydrophobic or a “sticker” residue through a single nucleotide mutation. This approach leverages the minimal genetic alteration needed to induce significant changes in the physicochemical properties of the protein, enabling a decrease in chain solvation with minimal sequence modification. b, Sequence alignment of Protein E–synIDP variants generated using SnapGene. Aligned regions are highlighted in red, while unaligned or mutated residues are shown in white. c, Representative fluorescence microscopy images of cells expressing fusions of sfGFP-synIDPs in BL21(DE3) before and after phase transition. Scale bar represents 3 μm. d, Summary of phase separation scores (PScore) for evolved IDPs selected from plate-based selection based on different rounds of evolution. The dashed line indicates the mean PScore for each round and the solid black line represents the fitted trend curve using an asymmetric sigmoidal model. Statistical significance was determined using an ordinary one-way ANOVA test. e, Summary of the key mutations of amino acids across four rounds of evolution.
Extended Data Fig. 3 A selection method of the evolved IDPs exhibiting different thermoresponsive phase behaviors.
a. Schematics of the selection strategies for the evolution of synIDPs with hysteric behaviors. To identify synIDP variants exhibiting reversible thermoresponsive phase transitions, a three-round replica plating strategy was employed. Following the LCST- and UCST- selection described above, colonies from the first round that displayed temperature-dependent are considered potential candidates for reversible phase behavior. Each of the two induced plates incubated at 30 °C and 45 °C are then independently replicated onto fresh plates containing the same arabinose concentration but incubated under the opposite temperature condition for at least 12 h. This second round of selection aimes to assess the reversibility of the observed temperature-dependent growth phenotype, distinguishing reversible or irreversible phase transitions. A third round of replica plating is transferring colonies from the second set of plates back to the original temperature condition (30 °C or 45 °C). b. Evaluation of CFUs of DH5α under different temperature. Statistical significance was determined using two sample T-test. Data is represented as mean ± SD. n = 3 biological replicates. c. Representative confocal images of an rIDP, and an irIDP illustrating differences in thermal hysteresis. RLPWT and ELPWT serve as controls exhibiting reversible UCST- and LCST-type phase behavior, respectively. Scale bars represent 3 μm.
Extended Data Fig. 4 Evaluation of the performance of soluble IDPs (sIDPs).
a. The evolution landscape of evolved soluble IDPs. The panel shows fitness curves of the selected evolved soluble IDPs (sIDPs) from two rounds of evolution. selected: variants with growth curves within the blue-shaded area were chosen for further characterization. non-selected: variants with growth curves within the red-shaded area were excluded from further confocal microscopy characterizations. Selected variants were subcloned and fused with sfGFP for confocal characterization. The non-phase separable variants identified by confocal microscopy were termed sIDP1-6, respectively. n = 1. Scale bars represent 3 μm. b. Kyte-Doolittle hydropathy scores of the evolved soluble synIDPs. The hydropathy parameter is a rescaled Kyte-Doolittle hydropathy value ranging from 0 (least hydrophobic) to 9 (most hydrophobic). c. Evaluation of the expression of the TEV-sIDPs by SDS-PAGE from the soluble and insoluble fraction of the cell lysates. The arrows mark the positions of the target proteins on the bands. Prestained Kaleidoscope™ ladder was used as a molecular weight standard for all gels.
Extended Data Fig. 5 Evaluation of the effect of condensate formation by lsIDPs for ampicillin resistance.
a. Representative fluorescence microscopy images of cells expressing fusions of TF7-sfGFP-lsIDPs in DH5α. Scale bars represent 3 μm. b. Plate-based cellular survival assay for the evaluation of the functional capacity of different lsIDPs fusions. Statistical significance was determined using an ordinary one-way ANOVA test. Data is represented as mean ± SD. n = 3 biological replicates. p = 3.04 × 10⁻⁶ for 500 mg/L ampicillin. c. Evaluation of growth conditions of DH5α expressing TF7-sfGFP-lsIDPs fusion proteins under different concentrations of ampicillin. nc: DH5α cells harboring a bla plasmid and a plasmid encoding sfGFP-lsIDP6. Data is represented as mean ± SD. n = 3 biological replicates.
Supplementary information
Supplementary Information
Supplementary Figs. 1–4 and Tables 1–11.
Supplementary Table
Predicted disordered scores of evolved synIDPs in this study.
Source data
Source Data Figs. 1–5 and Extended Data Figs. 1–5
Source data for all the main and extended figures.
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Ma, Y., Yang, L., Chen, Y. et al. Directed evolution of functional intrinsically disordered proteins. Nat Chem Biol (2026). https://doi.org/10.1038/s41589-025-02128-3
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DOI: https://doi.org/10.1038/s41589-025-02128-3


