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FvHallucinator

The code for FvHallucinator is made available under the Rosetta-DL license as part of the Rosetta-DL bundle.

FvHallucinator designs sequences that fold into a desired Fv structure by leveraging a pretrained sequence-to-structure prediction DL model, DeepAb (Ruffolo et al. 2021 Patterns). We adapted the trDesign (Norn et al. 2021 PNAS) approach where the problem of predicting sequence given structure has been reframed as the problem of maximizing the conditional probability of a sequence given structure. In the case of the Fv, we are primarily interested in designing a subset of the residues (CDRs, VH-VL interface), so we split the sequence S into fixed and designable positions, SF and SD. We then seek the design subsequence SD that maximizes the conditional probability of the sequence S given a target structure T and the fixed sequence SF. For more details, please refer to Mahajan et al. 2022.

All hallucinated sequences from publication are available on Zenodo.

The FvHallucinator reository builds upon the DeepAb repository.

Related repositories

trDesign: https://github.com/gjoni/trDesign <br /> RFDesign: https://github.com/RosettaCommons/RFDesign <br /> DeepAb: https://github.com/RosettaCommons/DeepAb <br />

Requirements

FvHallucinator requires python3.6 or higher. For a full list of requirements, see requirements.txt. For folding hallucinated sequences with DeepAb, you will additionally need a PyRosetta license (for installing pyrosetta, use conda or with setup.py).

Getting Started

Start by setting up a python virtual environment (or conda) with python3.6 or higher

python3 -m venv <path_to_env> 
source <path_to_env>/bin/activate
# Use the requirements.txt file to install dependencies
python3 -m pip install -r requirements.txt

Download pretrained DeepAb model

Pretrained DeepAb models need 330MB of free space. To download, run the following commands in your terminal.

wget https://data.graylab.jhu.edu/ensemble_abresnet_v1.tar.gz
tar -xvzf ensemble_abresnet_v1.tar.gz

Move the unzipped folder to <path_to_repo>/trained_models. The hallucinate.py script expects the model weights to be present in <path_to_repo>/trained_models/ensemble_abresnet/*.pt

Designing CDR loops with FvHallucinator

We recommend running hallucination on GPUs. Designs can be generated in parallel.

Unrestricted hallucination

To design CDR loops for a target CDR conformation, run unrestricted hallucination. In this mode of hallucination, sequences are only constrained by the target structure/conformation.

The pipeline requires all pdbs to be chothia-numbered. To obtain chothia-numbered pdbs, we recommend Abnum or ANARCI. Below is an example bash script (also see examples/run_hallucination.sh). (For all options, run python3 hallucinate.py -h)

#!/bin/bash

# activate virtual environment

# set pythonpath
export PATH_TO_REPO=<path_to_repo>
export PYTHONPATH=$PATH_TO_REPO:$PYTHONPATH

# chothia-numbered target structure for the Fv region
# example pdb for Trastuzumab Fv from data
TARGET_PDB=$PATH_TO_REPO/data/1n8z.truncated.pdb

# name of the output folder
PREFIX=$PATH_TO_REPO/examples/hallucination_cdrh3

# Generating 50 designs; recommended number of designs for cdrh3 is > 500.
start=0
stop=50

# --seed <> manual seeding each design with a different seed
# --suffix <> suffix to use for each design
# disallow the method from designing cysteines at all positions

for ((j = $start; j < $stop; j++)); do
python3 $PATH_TO_REPO/hallucinate.py \
  --target $TARGET_PDB \
  --iterations 50 \
  --suffix $j \
  --prefix $PREFIX \
  --seed $j \
  --cdr_list h3 \
  --disallow_aas_at_all_positions C
done

This script will generate hallucination trajectories and final sequences in $PREFIX/trajectories/

Designing any subsequence on the Fv

It is also possible to design other subsequences on the Fv regions with the following options:

--indices <string of indices to design with chains and chothia numbering> # e.g. h:20,31A/l:56,57
--hl_interface # design residues at the Vh-Vl interface (only non-cdr residues)
--framework # design all framework residues
--exclude <string of indices to exclude from design with chains and chothia numbering> # e.g. h:31A,52/l:56,57
# --exclude can be combined with --hl_interface, --framework, --cdr_list

If no design region is specified, the full Fv will be designed. This mode was not explored in the published work and we do not recommend it.

Post-processing and generating sequence logos

python3 $PATH_TO_REPO/process_designs.sh \
  --trajectory_path $PREFIX \
  --target $TARGET_PDB \
  --cdr h3 \
  --outdir $PREFIX/results #where the post-processing results will be stored

Results will include sequences of all CDR H3 designs in the file $PREFIX/results/sequences_indices.fasta, full Fv sequence of all designs in $PREFIX/results/sequences.fasta and sequence logos.

To compare hallucinated designs with PyIgClassify, you can additionally specify the path for PyIgClassify database. The latest version of this database can be downloaded from here. Alternatively, you can use the database used to generate data for the publication from data/cdr_clusters_pssm_dict.pkl with the option:

--cdr_cluster_database data/cdr_clusters_pssm_dict.pkl

This option only works with the option --cdr <cdr_name>.

For post-processing designs at the Vh-Vl interface, we additionally use ANARCI. This must be installed as described here. If ANARCI is not installed, FR scores will not be calculated.

Hallucination with wildtype seeding

Design positions can be initialized with residues from the starting antibody (target_pdb) instead of random initialization with --seed_with_WT.

Restricted hallucination

You can additionally guide hallucination towards relevant sequence spaces with sequence based losses as described below.

Sequence-restricted hallucination

This mode adds a loss during optimization to keep the designed sequence close to the starting sequence. To enable this loss set a non-zero weight for sequence loss with --seq_loss_weight 25 , where the weight determines the relative weight of the sequence loss and geometric loss. We recommend weights between 10-30. A higher weight will lead to designs closer to starting sequence and vice-versa.

Motif-restricted hallucination

This mode adds a loss during optimization to sample specified design positions from a restricted set of amino acids at a desired frequency/proportion. For example, to specify that position 100A (must be chothia numbered) on the CDR H3 loop, samples tyrosine and trytophan in equal proportions use options,

--restricted_positions_kl_loss_weight 100 \ #recommended loss weight
--restrict_positions_to_freq h:100A-W=0.50-Y=0.50 \

Other options

For a full list of options, run python3 hallucinate.py -h .

Folding hallucinated sequences with DeepAb

For folding hallucinated sequences with DeepAb and obtaining RMSDs, run:


# sequences.fasta file is generated by process_designs.py
# See examples/03_forward_folding.sh for a parallel version using dask distributed

start_run=0
end=10
python3 $PATH_TO_REPO/generate_fvs_from_sequences.py $TARGET_PDB \
 $DIR/results/sequences.fasta \
 --pdbs_from_model \
 --decoys 5 \
 --outdir $DIR \
 --scratch_space $DIR/tmp_scratch \
 --slurm_cluster_config config.json \
 --cdr_list h3 \
 --start ${start_run} \
 --end ${end}

# consolidate designs from all folding runs 
python3 $PATH_TO_REPO/generate_fvs_from_sequences.py $TARGET_PDB \
 $DIR/results/sequences.fasta \
 --plot_consolidated_funnels \
 --path_forward_folded $DIR/forward_folding \
 --outdir $DIR \
 --cdr_list h3 \
 --start ${start_run} \
 --end ${end}

We recommend running folding on a cluster (cpus). When the cluster option is enabled with --slurm_cluster_config config.json , dask will generate decoys in parallel. Using options --start and --end , many such scripts can be run in parallel to fold chunks (e.g. 0-10, 10-20, 100-200 etc.) of designed sequences. See examples/03_forward_folding.sh for a parallel version using dask distributed.

Example config file for slurm cluster

{
	"cores": 1,
	"memory": "9GB",
	"processes": 1,
	"queue": "<queue name>",
	"job_cpu": 2,
	"walltime": "10:00:00"
}

The folded pdbs will be in $DIR/forward_folding/ and the consolidated root-mean-square-deviations with respect to the target pdb will be in $DIR/forward_folding/results

Virtual Screening with Rosetta

To virtually screen hallucinated designs, provide a pdb with the structure of the antibody (Fv only) and the antigen and run:

python3 $PATH_TO_REPO/generate_complexes_from_sequences.py $TARGET_PDB_COMP \
 $DIR/results/sequences_indices.fasta \
 --get_relaxed_complex \ #this option is for virtual screening
 --partner_chains HL_X \ #provide chain names for antibody and antigen chains separated by an underscore
 --outdir $DIR \
 --cdr_list h3 \
 --start ${start_run} \
 --end ${end} \
 --slurm_cluster_config config.json \
 --scratch_space $DIR/tmp_scratch_dg

# consolidate from parallel runs and screen
python3 $PATH_TO_REPO/generate_complexes_from_sequences.py $TARGET_PDB \
 $DIR/results/sequences_indices.fasta \
 --plot_consolidated_dG \
 --outdir $DIR \
 --cdr h3 \
 --start ${start_run} \
 --end ${end}

Filtering final set of designs for folding and binding

To obtain designs that satisfy both folding and binding criteria, run:

python3 $PATH_TO_REPO/filter.py $TARGET_PDB_COMP \
 --csv_forward_folded $DIR/forward_folding/results/consolidated_ff_lowest_N010.csv \
 --csv_complexes $DIR/virtual_binding/relaxed_mutants_data/results/improved_dG_sequences_0-10.csv \
 --rmsd_filter H3,2.0 \
 --outdir $DIR/results_filtered_output \
 --cdr_list h3

Here, we selected designs wth CDR H3 RMSD less than or equal to 2.0 angstrom. You can select based on multiple thresholds as a json file with the option

--rmsd_filter_json <json file>  # specify CDR RMSD cutoffs with respect to the starting antibody

Citations

Mahajan, S. P., Ruffolo, J. A., Frick, R., & Gray, J. J. A deep learning framework to hallucinate structure-conditioned and antigen-specific antibodies. bioRxiv 2022.06.06.494991 (2022)