Creating Highly Specific Chemically Induced Protein Dimerization Systems by Stepwise Phage Selection of a Combinatorial Single-Domain Antibody Library

* These authors contributed equally
Biochemistry

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Summary

Creating chemically induced protein dimerization systems with desired affinity and specificity for any given small molecule ligand would have many biological sensing and actuation applications. Here, we describe an efficient, generalizable method for de novo engineering of chemically induced dimerization systems via the stepwise selection of a phage-displayed combinatorial single-domain antibody library.

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Gomez-Castillo, L., Watanabe, K., Jiang, H., Kang, S., Gu, L. Creating Highly Specific Chemically Induced Protein Dimerization Systems by Stepwise Phage Selection of a Combinatorial Single-Domain Antibody Library. J. Vis. Exp. (155), e60738, doi:10.3791/60738 (2020).

Abstract

Protein dimerization events that occur only in the presence of a small-molecule ligand enable the development of small-molecule biosensors for the dissection and manipulation of biological pathways. Currently, only a limited number of chemically induced dimerization (CID) systems exist and engineering new ones with desired sensitivity and selectivity for specific small-molecule ligands remains a challenge in the field of protein engineering. We here describe a high throughput screening method, combinatorial binders-enabled selection of CID (COMBINES-CID), for the de novo engineering of CID systems applicable to a large variety of ligands. This method uses the two-step selection of a phage-displayed combinatorial nanobody library to obtain 1) "anchor binders" that first bind to a ligand of interest and then 2) "dimerization binders" that only bind to anchor binder-ligand complexes. To select anchor binders, a combinatorial library of over 109 complementarity-determining region (CDR)-randomized nanobodies is screened with a biotinylated ligand and hits are validated with the unlabeled ligand by bio-layer interferometry (BLI). To obtain dimerization binders, the nanobody library is screened with anchor binder-ligand complexes as targets for positive screening and the unbound anchor binders for negative screening. COMBINES-CID is broadly applicable to select CID binders with other immunoglobulin, non-immunoglobulin, or computationally designed scaffolds to create biosensors for in vitro and in vivo detection of drugs, metabolites, signaling molecules, etc.

Introduction

CID systems, in which two proteins dimerize only in the presence of a small-molecule ligand (Figure 1), offer versatile tools for dissecting and manipulating metabolic, signaling, and other biological pathways1. They have demonstrated the potential in biological actuation, such as drug-controlled T cell activation2 and apoptosis3,4, for improving the safety and efficacy of adoptive T cell therapy. Additionally, they provide a new methodology for in vivo or in vitro detection of small-molecule targets. For example, CID proteins can be genetically fused with fluorescence reporter systems (e.g., fluorescence resonance energy transfer (FRET)5 and circularly permuted fluorescent proteins)6 for real-time in vivo measurements, or serve as affinity reagents for sandwich enzyme-linked immunosorbent assay (ELISA)-like assays.

Despite their wide applications, creating new CID systems that can be controlled by a given small-molecule ligand has major challenges. Established protein binder engineering methods including animal immunization7, in vitro selection8,9, and computational protein design10 can generate ligand binding proteins that function via binary protein-ligand interactions. However, these methods have difficulties creating a ligand-induced ternary CID complex. Some methods create CID by chemically linking two ligands that independently bind to the same or different proteins11,12,13,14,15,16 or rely on selecting binder proteins such as antibodies targeting preexisting small molecule-protein complexes17,18, and thus have a limited choice of ligands.

We recently developed a combinatorial binders-enabled selection of CID (COMBINES-CID) method for de novo engineering of CID systems19. This method can obtain the high specificity of ligand-induced dimerization (e.g., an anchor-dimerization binder dissociation constant, KD (without ligand)/KD (with ligand) > 1,000). The dimerization specificity is achieved using anchor binders with flexible binding sites that can introduce conformational changes upon ligand binding, providing a basis for the selection of conformationally selective binders only recognizing ligand-bound anchor binders. We demonstrated a proof-of-principle by creating cannabidiol (CBD)-induced heterodimers of nanobodies, a 12–15 kDa functional antibody fragment from camelid comprising a universal scaffold and three flexible CDR loops (Figure 2)20, which can form a binding pocket with adaptable sizes for small-molecule epitopes21,22. Notably, the in vitro selection of a combinatorial protein library should be cost-effective and generalizable for CID engineering because the same high-quality library can be applied to different ligands.

In this protocol and video, we focus on describing the two-step in vitro selection and validation of anchor (Figure 3A) and dimerization binders (Figure 3B) by screening the combinatorial nanobody library with a diversity higher than 109 using CBD as a target, but the protocol should be applicable to other protein libraries or small-molecule targets. The screening of CID binders usually takes 6–10 weeks (Figure 4).

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Protocol

1. Library construction

  1. Use a synthetic combinatorial single-domain antibody library with a diversity of ~1.23–7.14 x 109, as previously described19. While this protocol does not include library construction, it can be applied to other combinatorial binder libraries.

2. Biotinylation of ligand target or ligand

  1. Biotinylate the selected ligand, for example, CBD and tetrahydrocannabinol (THC)19, via various chemical synthesis strategies, depending on the suitable biotinylation sites of a target.

3. Anchor binder screening

  1. Beginning of selection
    1. Begin every round of selection by inoculating a single TG1-cell colony, freshly grown in 6 mL of 2YT at 37 ˚C and 250 revolutions per minute (rpm) to a 600 nm (OD600) absorbance of ~0.5. Incubate the cells on ice for the use in step 3.5.1.
  2. Negative selection with biotin-bound streptavidin beads
    1. Prepare the "negative selection beads" by washing 300 µL of streptavidin-coated magnetic beads using a magnetic separation rack, 3x with 0.05% phosphate-buffered saline with Tween buffer (PBST, 1 x PBS with 0.05% vol/vol Tween 20%) and 2x with 1 x PBS.
    2. Resuspend the beads with 1 mL of 1% casein in 1 x PBS (pH = 7.4), and saturate the beads by adding 5x the reported binding capacity using biotin. Incubate at room temperature (RT) on a rotator for 1 h.
    3. Wash the beads 5x using 0.05% PBST and 3x using 1 x PBS, for a total of eight washes.
    4. Add ~1013 phage particles in 1% casein/1% BSA in 1 x PBS (pH = 7.4) and incubate at RT on a rotator for 1 h.
    5. After incubation, collect the supernatant to be used in step 3.3.6.
  3. Positive selection with biotinylated ligand-bound streptavidin beads
    1. Prepare the "positive selection beads" using 1/2 the volume of the beads used for the "negative selection beads" following steps 3.2.1.
    2. Re-suspend the beads with 1 mL 1% casein in 1 × PBS, pH 7.4 and saturate the beads by adding 5x the full binding capacity calculated based on the manual using the biotinylated ligand of choice. Incubate at RT on a rotator for 1 h.
    3. Wash the beads 5x using 0.05% PBST and 3x using 1 x PBS, for a total of eight washes.
    4. Block the beads with 1 mL of 1% casein/1% BSA in 1 x PBS (pH = 7.4) and incubate at RT on a rotator for 1 h to prevent nonspecific binding between the phages and the streptavidin-coated magnetic beads.
    5. Wash the streptavidin-coated magnetic beads 3x using 0.05% PBST and one time using 1 x PBS, for a total of four washes.
    6. Resuspend the streptavidin-coated magnetic beads using the unbound phages taken from step 3.2.5 and incubate at RT on a rotator for 1 h.
    7. Extract the supernatant without disturbing the magnetic beads. Save the unbound phages as input, to be used in step 3.5.1.
    8. Wash the beads 10x using 0.05% PBST and 5x using 1 x PBS. In between every three washes transfer them to a new tube to avoid phages nonspecifically bound to the tube walls.
  4. Elution of phage-displayed nanobodies
    1. Competitively elute bound phages by adding 450 µL of the non-biotinylated ligand, using a concentration in the micromolar range (e.g., 10–50 µM) and incubating at RT on a rotator for 30 min. The selected ligand concentration for the competitive elution of bound phages is dependent on desired KD of the "anchor binder". Ligand concentrations can be relatively high in initial selection rounds and then decreased in later rounds.
    2. Collect supernatant and save the eluted phages as output, to be used in step 3.5.2.
  5. Input/output titrations and infection
    1. For input titration, prepare 10x serial dilutions in 1 x PBS up to 109-fold with the input phage from step 3.3.7. Use the 107–109 serial dilutions to do infections by transferring 10 µL input phage from each dilution to 70 µL TG1 cells (OD600 of ~0.5). Incubate at 37 ˚C for 45 min, plate the infected TG1 cells on three 90 mm 2YT-agar dishes containing 100 μg/mL ampicillin and 2% (wt/vol) glucose, and incubate overnight at 37 ˚C. From the overnight plates, phage input can be calculated as follows:
      Equation 1
    2. For output infection and titration, transfer the eluted phages from step 3.4.2 to 3 mL of TG1 cells (OD600 of ~0.5). Incubate in a water bath at 37 ˚C for 45 min. Then prepare 10x serial dilutions in 2YT up to 103-fold, plate each dilution on 90 mm 2YT-agar dishes, and incubate overnight at 37 ˚C. From the overnight plates, phage output can be calculated as follows:
      Equation 1
    3. Divide the remaining infected TG1 cells on three 150 mm 2YT-agar plates containing 100 μg/mL ampicillin and 2% (wt/vol) glucose. Incubate plates overnight at 37 ˚C.
  6. Library amplification and recovery for further rounds of selection
    1. Add 3 mL of 2YT per plate, scrape with a sterile cell scraper and collect all cells in a 50 mL conical tube. Mix the collected cells with sterile glycerol (20% wt/vol final concentration). Measure the OD600 of the mixture and make 3–5 stock aliquots. Store at -80 ˚C for long-term storage.
    2. For phage rescue, dilute the phagemid-containing TG1 bacterial mixture using 25 mL of 2YT media supplemented with 2% glucose and 100 μg/mL ampicillin to an OD600 of ~0.1. Culture cells at 37 ˚C and 250 rpm to an OD600 of ~0.5.
    3. Superinfect the cells by adding CM13 helper phage at 5 x 109 pfu/mL and incubate at 37 ˚C and 250 rpm for 45 min. The CM13 helper phage provides required phage coat proteins for the assembly of complete phage particles.
    4. Centrifuge the culture at 8,000 x g for 10 min to remove the glucose. Resuspend the cells using 50 mL of 2YT media supplemented with 100 μg/mL ampicillin and 50 μg/mL kanamycin and incubate at 25 ˚C and 250 rpm overnight.
    5. Centrifuge the cells from the overnight culture at 9,000 x g, 4 ˚C for 30 min. Transfer supernatant to a new tube and precipitate phages in the supernatant using 1/5 volume PEG/NaCl solution (20% wt/vol polyethylene glycol-6,000 and 2.5 M NaCl). Mix gently and place on ice for 1 h.
    6. Collect phage particles by centrifugation using 12,000 x g at 4 ˚C for 30 min. Resuspend the pellets using 1 mL of 1 x PBS, and transfer the suspension to a microcentrifuge tube. Centrifuge the tube at 20,000 x g and 4 ˚C for 10 min to remove residual bacteria.
    7. Transfer the supernatant to a new microcentrifuge tube without disturbing the bacterial pellet. Use a 1:100 dilution to measure the absorption at 269 nm and 320 nm. The total number of phages can be calculated using the following formula23:
      Equation 3
    8. Store phage library at 4 ˚C for short-term use or with 25% glycerol at -80 ˚C for long-term storage.
    9. Repeat rounds of selection (steps 3.1–3.6) for 3–6 rounds or until desired enrichment is observed (refer to Results section). Plate and pick single clones (section 4) in order to characterize their affinity and specificity to the ligand (sections 5–7).

4. Single clone isolation

  1. To isolate individual clones from an enriched sublibrary, prepare 10x serial dilutions of the phage-infected TG1 cells (step 3.5.2). Plate serial dilutions on 90 mm 2YT-agar dishes containing 100 μg/mL ampicillin and 2% (wt/vol) glucose and incubate at 37 ˚C overnight.
  2. From the overnight plates, pick single colonies into 250 μL of 2YT media supplemented with 100 μg/mL ampicillin per well in sterile deep-well plates and grow at 37 ˚C overnight.
  3. From the overnight cultures, inoculate 10 µL into 500 µL of fresh 2YT media supplemented with 100 μg/mL ampicillin.
  4. Grow cells to an OD600 of ~0.5, add CM13 helper phage at 5 x 109 pfu/mL and incubate at 37 ˚C and 250 rpm for 45 min.
  5. Add 500 µL of 2YT media supplemented with 100 μg/mL ampicillin and 50 μg/mL kanamycin. Incubate at 25 ˚C and 250 rpm overnight.
  6. Centrifuge the deep-well plates from the overnight cultures at 3,000 x g for 10 min. Collect the supernatant containing the phage particles without disturbing the cell pellet.
  7. Phage particles can be used for ELISA to determine the specificity of the selected clones to the ligand. Biotin or a structural homolog of the target can be used as a negative control.

5. Anchor binder validation by ELISA

  1. Coat 96 well ELISA plates using 100 μL of 5 μg/mL streptavidin in coating buffer (100 mM carbonate buffer, pH = 8.6) at 4 ˚C overnight.
  2. Wash the ELISA plates 3x using 0.05% PBST and add 100 μL of 1 μM biotinylated target to the target wells. Add 100 μL of 1 μM biotin or target homolog to the control wells. Incubate at RT for 1 h.
  3. Wash plates 5x using 0.05% PBST and block nonspecific binding by adding 300 µL of 1% casein in 1 x PBS. Incubate at RT for 1 h.
  4. Wash the ELISA plates 3x using 0.05%-PBST and add the purified phage supernatant. Incubate for 1 h at RT.
  5. Wash the ELISA plates 10x using 0.05% PBST and add 100 μL horseradish peroxidase (HRP)-M13 major coat protein antibody (1:10,000 dilution with 1 x PBS with 1% casein). Incubate at RT for 1 h.
  6. Wash the ELISA plates 3x using 0.05% PBST and add 100 μL tetramethylbenzidine (TMB) substrate. Incubate for 10 min or until a visible color change is observed. Stop the reaction by adding 100 μL of 1 M HCl. Read the plate at 450 nm on a spectrophotometer.
  7. For protein expression and purification, choose the clones showing high affinity and specificity for the target (see Discussion).

6. Protein expression, purification, and biotinylation

  1. As previously reported19, subclone selected clones from section 5 and express as C-terminal Avi-tagged and His-tagged nanobodies.
  2. Express selected nanobodies in the periplasm of E. coli WK6 cells (typically in 1 L culture), release by osmotic shock, and purify using a nickel-NTA column (see Table of Materials).
  3. Exchange buffer with a desalting column (1 x PBS with 5% glycerol; see Table of Materials).
  4. Biotinylate nanobodies using a commercial kit (see Table of Materials) for further use.

7. Anchor binder characterization by BLI

  1. Analyze the binding affinity and kinetics of selected anchor binders by immobilizing 200 nM biotinylated anchor binders on streptavidin biosensors (see Table of Materials) with binding assay buffer (1 x PBS (pH = 7.4), 0.05% Tween 20, 0.2% BSA, 3% methanol).
  2. Calculate dissociation constants (KD) of anchor binder-ligand interactions by steady-state analysis using data analysis software (see Table of Materials). Obtained KD values typically range from single- to double-digit micromolar.

8. Dimerization binder screening

NOTE: The biopanning screening of "dimerization binders" is similar to that of anchor binders, except for two critical steps: 1) Dimerization binders are selected using a selected biotinylated anchor binder and the anchor binder-ligand complex for the negative and positive selections, respectively. 2) During the elution step, 100 mM triethylamine is used to elute positively selected phages that were only bound to the anchor binder--ligand target complex. The 100 mM trimethylamine solution (pH = 11.5) is used to elute positive clones by disrupting the protein interactions.

  1. Beginning of selection
    1. Begin every round of selection by inoculating a single TG1 cell colony, freshly grown on a minimal media, in 6 mL 2YT at 37 ˚C and 250 rpm to an OD600 of ~0.5. Incubate cells on ice.
  2. Removal of negatively selected nanobodies
    1. Prepare the "subtraction tube" by using 400 µL of streptavidin-coated magnetic beads and follow step 3.2. However, instead of saturating with biotin, add 5x the calculated full binding capacity using the selected biotinylated anchor binder and save the unbound phages to be used in step 8.3.3.
  3. Selection of positively selected nanobodies
    1. Prepare the "capturing tube" by using 1/2 the volume of streptavidin-coated magnetic beads used for the "subtraction tube" and following steps 3.3.2 to 3.3.3. However, instead of saturating with the biotinylated ligand, add five times the calculated full binding capacity using the selected biotinylated anchor binder.
    2. To form the anchor binder-ligand complex for the positive dimerization binder selection, add a high enough concentration of non-biotinylated ligand. This will allow most streptavidin-bound anchor binder to form the ligand-bound complex.
    3. Follow steps 3.3.3 to 3.3.8, using the unbound phages taken from the "subtraction tube".
  4. Elution of positively selected nanobodies
    1. Elute the phages bound to the anchor binder-ligand complex by adding 450 µL of 100 mM triethylamine, and incubating at RT on a rotator for 10 min.
    2. Collect the competitively eluted phages and follow steps 3.4.1 to 3.4.2.
  5. Further rounds of dimerization binder selection
    1. Follow steps 3.5 and 3.6 to amplify and recover the library in order to perform further rounds of selection. Repeat rounds of selection for 3–6 rounds or until desired enrichment is observed. Plate and pick single clones (refer to section 4) in order to characterize their affinity and specificity to the target.

9. Dimerization binder characterization by ELISA

  1. Follow the steps in section 4 to isolate individual clones for characterization via ELISA.
  2. To test the affinity of dimerization binder candidates to the anchor binder-ligand complex, coat the ELISA target plate using 100 μL of 100 nM biotinylated anchor binder. After incubation for 1 h, add 1 μM of the ligand target to form the anchor binder-ligand complex.
  3. The control plate should be coated using the biotinylated anchor binder alone to screen out clones that can also bind to the free anchor binder. Add 100 μL of 100 nM biotinylated anchor binder and incubate at RT for 1 h.
  4. Follow sections 5.3–5.7.

10. Dimerization binder characterization by BLI

  1. The binding affinity and kinetics of dimerization binders for the anchor binder--ligand complex can be analyzed by immobilizing biotinylated dimerization binders on streptavidin (SA) biosensors with the binding assay buffer and then assayed with 1 μM anchor binder pre-equilibrated with serial dilutions of the ligand. The KD, kon, and koff of the interactions can be calculated using our reported method19.

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Representative Results

We describe the two-step in vitro selection and validation of anchor and dimerization binders by screening the combinatorial nanobody library with a diversity higher than 109 using CBD as a target. Assessing the enrichment of the phage biopanning during the successive rounds of selection for both anchor and dimerization binders is important. Typical enrichment results after 4–6 rounds of selection as shown in Figure 5 are a good indication that there is a high ratio of potential hits in the sublibraries, so further rounds of selection might not be necessary.

Single-clone ELISA is suitable for analyzing the relative binding affinity and selectivity of anchor and dimerization binders. Figure 6A is a representative anchor binder selection result after six rounds of biopanning. Clones showing high (e.g., #87) or low (e.g., #27) ligand selectivity can be compared. High selectivity clones should be chosen as anchor binder candidates. Likewise, Figure 6B shows the dimerization binder selection results after four rounds of biopanning. We typically observed clones that formed a heterodimer with the immobilized anchor binder only with the ligand (e.g., #49) or without (e.g., #80). The former, showing dimerization specificity, should be selected for further validation.

Anchor binder ELISA relies on the use of the biotinylated target. Thus, we need to use BLI to further confirm the binding to the non-labelled target. BLI also allows the characterization of binding kinetics. Representative BLI results of anchor and dimerization binders are shown in Figure 7A and 7B, respectively. The left panels show the ligand concentration-dependent binding, suggesting that they are suitable for constructing a CID system. The right panels show the negative controls. The calculated KD of anchor and dimerization binder interactions in the presence of the ligand typically ranged from double-digit nanomolar to double-digit micromolar. They might vary depending on the ligand and the combinatorial library of choice.

Analytical size-exclusion chromatography (SEC) was performed to confirm the heterodimer formation between anchor and dimerization binders. A dimerization peak was observed when the anchor and dimerization binders and CBD were mixed (Figure 8A, red line). In contrast, no dimerization peak was detected in the absence of CBD (Figure 8A, blue line) or when each binder was loaded to the column alone (Figure 8B). The chemical crosslinking was used to stabilize CID complexes, and crosslinked nanobodies have slightly increased sizes corresponding to earlier eluted peaks.

Figure 1
Figure 1: Mechanism of chemically induced protein dimerization. Please click here to view a larger version of this figure.

Figure 2
Figure 2: Schematic of the generation of a synthetic nanobody combinatorial library. The library is constructed by using a universal nanobody scaffold and incorporating designed distributions of amino acids to each randomization position in three complementarity-determining regions (CDRs) by a Trinucleotide Mutagenesis (TRIM) technology 24. Please click here to view a larger version of this figure.

Figure 3
Figure 3: Flowchart of (A) anchor and (B) dimerization binder screening. Please click here to view a larger version of this figure.

Figure 4
Figure 4: Timeline of COMBINES-CID. Please click here to view a larger version of this figure.

Figure 5
Figure 5: Enrichment of phage titers following each round of biopanning for the anchor binder selection. Please click here to view a larger version of this figure.

Figure 6
Figure 6: Representative ELISA results showing positive (+) and negative (*) clones. (A) Anchor binder ELISA results from 96 randomly picked clones after six rounds of selection. (B) Dimerization binder ELISA results of 96 randomly picked clones after four rounds of selection. Please click here to view a larger version of this figure.

Figure 7
Figure 7: Anchor and dimerization binder kinetic analysis by BLI. (A) Analysis of the anchor binder with unlabeled CBD (left) and THC (right). Biotinylated anchor binder was immobilized on Super Streptavidin (SSA) biosensors titrated with different concentrations of CBD. Measured data for CBD binding (red curves) were globally fitted (grey lines). (B) Left, BLI analysis of an SA biosensor-immobilized dimerization binder binding to the anchor binder preequilibrated with different concentrations of CBD. Right, the anchor binder concentration was titrated and bound to the immobilized dimerization binder in the absence of CBD. Please click here to view a larger version of this figure.

Figure 8
Figure 8: SEC analysis of the heterodimerization between the anchor and dimerization binders. (A) The dimerization and anchor binders (5 µM each) in the presence or absence of CBD were crosslinked by 100 µM bis-N-succinimidyl-(pentaethylene glycol) ester for 30 min at RT before the analysis. Elution volumes of protein standards are marked by triangles. (B) Non-crosslinked anchor and dimerization binders (30 µM each) were injected separately. Chromatograms in A and B are shown in different Y scales. Please click here to view a larger version of this figure.

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Discussion

It is critical to choose the correct concentrations of input phage libraries for different rounds of biopanning. We typically started from an input library of ~1012–1013 phage particles with a diversity >109, allowing ~100–1,000 copies of each phage clone to be presented in the pull-down assay. If the phage concentration in a binding assay is too high or low, the likelihood of nonspecific binding or loss of positive clones will increase. The anchor or dimerization binder selection normally consists of three to six rounds of biopanning, and the output phage counts usually start from ~104 and increases to ~108–109. It is suitable to pick single clones for ELISA validation after observing such enrichment. Additional rounds of biopanning might decrease the chances of identifying suitable low-abundance positive clones.

It is important to set up suitable negative controls and selections to enhance the success of the selections. For example, the use of structural analogs of ligand targets will facilitate the selection of ligand specificity. In our work, a highly similar analog, THC, was used as a control for CBD in the ELISA and BLI validation of anchor and dimerization binders19. In the dimerization binder selection, if anchor binders have relatively low ligand binding affinity, both free and ligand-bound anchor binders can be presented as targets in the positive selection. Thus, it is important to thoroughly remove binders that bind to free anchor binders during the negative selection. This can be achieved by performing multiple rounds of the subtraction with free anchor binders.

A limitation of our protocol is that target molecules need to be biotinylated for the anchor binder selection and only one or a few anchor binders can be used for the dimerization selection. The use of biotinylated targets can enrich binders that partly bind to the linker between biotin and targets. Thus, it is important to validate hits using unlabeled targets by BLI or other techniques. Choosing a single or a few anchor binders for dimerization binder selection can decrease the chance of identifying CID systems with suitable sensitivity and specificity. Thus, the multiplexing capability of the selection awaits further improvement by coupling to other techniques—for example, single-molecular-interaction sequencing (SMI-Seq) which enables a "library-by-library" protein-protein interaction screening25.

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Disclosures

A provisional patent related to this work has been filed by the University of Washington.

Acknowledgments

This work was supported by the University of Washington Innovation Award (to L.G.), a grant from the U.S. National Institutes of Health (1R35GM128918 to L.G.), and a startup fund of the University of Washington (to L.G.). H.J. was supported by a Washington Research Foundation undergraduate fellowship. K.W. was supported by an undergraduate fellowship from the University of Washington Institute for Protein Design.

Materials

Name Company Catalog Number Comments
1-Step Ultra TMB ELISA substrate solution Thermo Fisher Scientific 34029
Agar Thermo Fisher Scientific BP1423-2
Amicon Ultra-15 Centrifugal Filter unit (3 kDa cutoff) Millipore UFC900324
Ampicillin Thermo Fisher Scientific BP1760-25
Bio-Rad Protein Assay Kit II Bio-Rad 5000002
BirA biotin-protein ligase standard reaction kit Avidity BirA500
Bovine Serum Albumin (BSA) Sigma-Aldrich A2153-50G
Casein Sigma-Aldrich C7078-1KG
CM13 Helper phage Antibody Design Labs PH020L
D-(+)-Glucose monohydrate Alfa Aesar A11090
Dynabeads M-280 Streptavidin Thermo Fisher Scientific 11205D
DynaMag-2 Magnet Thermo Fisher Scientific 12321D
EDTA Thermo Fisher Scientific BP120-1
Fast DNA Ladder New England Biolabs N3238S
FastDigest BglI Thermo Fisher Scientific FD0074
Glycerol Thermo Fisher Scientific BP229-1
HiLoad 16/600 Superdex 200 pg GE Healthcare 28989335
HiPrep 26/10 Desalting Column GE Healthcare 17508701
HisTrap-FF-1ml GE Healthcare 11000458
Imidazole Alfa Aesar 161-0718
IPTG Thermo Fisher Scientific 34060
Kanamycin Thermo Fisher Scientific BP906-5
M13 Major Coat Protein Antibody Santa Cruz Biotechnology sc-53004
NaCl Sigma-Aldrich S3014-500G
NanoDrop 2000/2000c Spectrophotometers Thermo Fisher Scientific ND-2000
Nunc 96-Well Polypropylene DeepWell Storage Plates Thermo Fisher Scientific 260251
Nunc MaxiSorp Thermo Fisher Scientific 44-2404-21
Octet RED96 ForteBio N/A
pADL-23c Phagemid Vector Antibody Design Labs PD0111
PEG-6000 Sigma-Aldrich 81260-1KG
Platinum SuperFi DNA Polymerase Invitrogen 12351010
PureLink PCR Purification Kit Thermo Fisher Scientific K310001
QIAprep Spin M13 Kit Qiagen 27704
Recovery Medium Lucigen 80026-1
SpectraMax Plus 384 Molecular Devices N/A
Sucrose Sigma-Aldrich S0389-1KG
Super Streptavidin (SSA) Biosensors ForteBio 18-5057
Superdex 75 increase 10/300 GL Column GE Healthcare 28-9909-44
T4 DNA Ligase Thermo Fisher Scientific 15224-025
TG1 Electrocompetent Cells Lucigen 60502-1
Triethylamine Sigma-Aldrich 471283-100mL
Trizma Base Sigma-Aldrich T1503
Tryptone Thermo Fisher Scientific BP9726-5
Tween 20 Thermo Fisher Scientific BP337-500
Yeast Extract Thermo Fisher Scientific BP1422-2
Zeba Spin Desalting Column Thermo Fisher Scientific 89882

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