Understanding the 3D structure of biological molecules like proteins and nucleic acids is essential for studying their functions and interactions. This understanding lays the foundation for designing therapeutic molecules that target important cellular processes. Over the past few years, deep learning models like AlphaFold have advanced protein and nucleic acid structure prediction. However, there remains an opportunity for improvement, especially in predicting binding complexes critical for drug discovery. Recently, Chai Discovery developed a new multi-modal foundation model, Chai-1, to advance molecular structure prediction. Let’s get into the details of this model!
Table of Contents
The Chai-1 Model
As mentioned above, Chai-1 is a multi-modal foundation model recently developed by Chai Discovery for molecular structure prediction. It is capable of predicting the 3D structures of biomolecules like proteins, nucleic acids (DNA and RNA), small molecules and their interactions from sequence data alone or with additional inputs.
How Chai-1 Works
Chai-1 uses a Transformer-based neural network trained on large biological datasets. It takes biomolecular sequences as input and first encodes them into numerical representations, using additional data sources such as MSAs and language model embeddings to help identify evolutionary patterns and provide residue-level context.
It then employs a Transformer architecture using self-attention, which allows every part of the input to interact with every other part, helping the model capture long-range relationships across residues. Lastly, Chai-1 decodes this contextualized representation to predict 3D coordinates for each atom and outputs the predicted structure in standard formats like PDB.
Performance Evaluation of Chai-1
The model was tested on several renowned benchmarks, and it achieved competitive results. It obtained a 77% success rate on PoseBusters protein-ligand benchmark compared to 76% by AlphaFold3. On CASP15 protein structure prediction, it achieved a Cα LDDT of 0.849 versus 0.801 by ESM3.
Remarkably, Chai-1 can also run in single sequence mode without MSAs and still maintain good performance. Moreover, it outperformed AlphaFold-Multimer in multimer protein folding prediction at 69.8% versus 67.7% DockQ success rate. This makes it the first model to predict multimers using only sequences.
Key Features of Chai-1
1. Language Model Embeddings
The model uses language model embeddings to power single-sequence capabilities. This allows predictions without multiple sequence alignments (MSAs), preserving much of its accuracy. This makes it faster and more practical for large-scale applications.
2. Experimental Constraints
Chai-1 can incorporate experimental data like contacts between interacting molecules. Such restraints improve difficult predictions by informing the model.
3. Protein-Ligand Prediction
It matches industry-leading accuracy in docking small molecules to target proteins. Its ability to condition on protein shapes from “docking tasks” highlights its prompt-followability.
4. Multimeric Protein Prediction
For protein complex assembly, this model outperforms competitors with or without MSAs. This makes it optimal for exploring sequence diversity like immunological targets rapidly.
5. Antibody-Antigen Binding
The model predictions on antibodies improve with added interaction site or contact information, showing its potential to aid biotherapeutic design.
6. Prompting with Experimental Data
Chai-1 can be conditioned on restraints derived from experimental techniques like epitope mapping to improve performance. Using just a few contacts doubles the accuracy of antibody-antigen prediction.
Free Public Access
The model can be accessed freely via an online interface at lab.chaidiscovery.com for both academic and commercial use, including drug discovery. Its code is also released on GitHub for non-commercial use.
Future Scope of Chai-1 and Chai Discovery
Chai Discovery aims to transform biology into an engineering discipline through further advancing AI foundation models. Chai-1 marks only the beginning of this journey. Future models will integrate additional capabilities for tasks like predicting and reprogramming interactions between biochemical molecules. Investors like OpenAI, Conviction, Neo, Thrive Capital and Dimension supports Chai Discovery in this mission.
For more technical details, please visit the technical report.
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