Structural and energetic landscape of the human HOP-PrP^C Axis: Multi-domain stabilization and peptide-mediated...

The heat shock protein 70 (HSP70)-HSP90 organizing protein (HOP), also known as STIP1, is a vital co-chaperone that mediates the transfer of oncogenic client proteins between HSP70 and HSP90. While HOP's canonical role as a co-chaperone involves coordinating HSP70 and HSP90 activity to facilitate the folding, maturation, and stabilization of selected oncogenic client proteins, the interaction between HOP and the cellular prion protein (PrP^C) has recently emerged as a significant driver of tumor progression, metastasis, and the maintenance of cancer stem cell characteristics. This study utilizes an integrated computational pipeline, including molecular docking and extensive molecular dynamics (MD) simulations with a cumulative sampling time approaching 1.5 μs, to provide the first comprehensive structural roadmap of the human HOP-PrP^C interaction. Our results elucidate a hierarchical binding mechanism where the PrP^C protein initially targets the TPR2A domain of HOP with a binding affinity of -88.01 ± 10.88 kcal/mol, subsequently recruiting the TPR2B and DP2 modules to achieve a high-affinity "locked" state of -152.38 ± 29.79 kcal/mol. Critical interface hotspots were identified at HOP residues Leu187 and Pro211 via saturation mutagenesis. Furthermore, we evaluated the inhibitory potential of repurposed small molecules and the amphipathic peptide Melittin. While the FDA-approved drug Tarceva (Erlotinib) restricts PrP engagement to the TPR2A domain by inducing structural compaction in HOP, Melittin emerged as a superior inhibitor. Melittin binding at the TPR1-TPR2A interface triggers the complete physical detachment of the PrP^C peptide. Furthermore, against the full-length PrP^C protein, Melittin dismantling the multi-domain 'locked' state and causes a drastic reduction in binding affinity, restricting the protein almost entirely to the TPR2A domain. These findings demonstrate that the conformational plasticity of HOP can be strategically exploited for targeted protein-protein interaction (PPI) disruption in cancer therapy.