Liu, J.; Chen, H.; Zhang, Y.

Understanding protein-protein interactions (PPIs) is crucial for deciphering cellular processes and guiding therapeutic discovery. While recent protein language models have advanced sequence-based protein representation, most are designed for individual chains and fail to capture inherent PPI patterns. We introduce a novel Protein-Protein Language Model (PPLM) that jointly encodes interacting protein pair representations. Building on this foundation, we develop three specialized predictors--PPLM-PPI, PPLM-Affinity, and PPLM-Contact--targeting binary interaction, binding affinity, and interface contact predictions, respectively. Large-scale experiments show that PPLM-PPI achieves state-of-the-art performance across different species on binary interaction prediction, while PPLM-Affinity outperforms both ESM2 and structure-based methods on binding affinity modeling, particularly on challenging cases including antibody-antigen and TCR-pMHC complexes. PPLM-Contact further surpasses existing PPI contact predictors on inter-protein contact prediction and interface residue recognition, including those deduced from cutting-edge complex structure predictions. Together, these results highlight the potential of co-represented language models to advance computational modeling of PPIs.