Researchers at the Nano Life Science Institute (WPI-NanoLSI), Kanazawa University, in collaboration with Osaka University and the National Institutes for Quantum Science and Technology, have uncovered a previously unknown mechanism behind the activation of the Met receptor—a key player in tissue regeneration and cancer progression. Their findings, published in the journal ACS Nano, reveal that hepatocyte growth factor (HGF) binding to the membrane-distal domain of Met promotes dimerization at the membrane-proximal domain, subsequently triggering receptor activation.
Understanding the Met Receptor
Cell-cell communication primarily occurs through the activation of transmembrane receptors, such as growth factor and cytokine receptors. Understanding the activation mechanisms of growth factor receptors has been a hot topic in structural biology. The Met receptor, the receptor for HGF, plays definitive roles in morphogenesis, tissue regeneration, and cancer metastasis. The activation of Met is initiated by HGF binding, which induces receptor dimerization.
While high-resolution techniques such as X-ray crystallography and cryo-electron microscopy (cryo-EM) have provided valuable insights into this process, they have been limited to truncated forms of Met, leaving the structure of the physiological receptor dimer unresolved. Elucidating the structure of the full-length receptor dimer in its native cellular environment poses a significant challenge due to the difficulty of isolating the receptor dimer from living cells and achieving high-resolution structural characterization.
Methodology
In this study, the physiological Met dimer was chemically cross-linked in living cells prior to isolation. A multifaceted approach was employed to elucidate its structure and investigate the underlying dimerization mechanism. The receptor was visualized at the single-protein level using high-speed atomic force microscopy (HS-AFM).
Key Findings and Mechanisms
HS-AFM imaging revealed that Met and HGF form a 2:2 complex, with two HGF molecules positioned at the periphery of the dimer. The SP domains of HGF interact with two closely associated Sema domains of Met, supported by normal mode flexible fitting. This relationship is crucial for understanding how receptor activation is facilitated.
| Technique Used | Description |
|---|---|
| HS-AFM Imaging | Visualized the Met and HGF complex at the single-protein level. |
| Split-Luciferase Assay | Demonstrated HGF-induced Met dimerization at IPT4 domain. |
| Molecular Dynamics Simulations | Characterized the stable connection mediated by IPT4 dimerization. |
The IPT regions of Met are stably connected while exhibiting significant conformational flexibility. The split-luciferase-based detection of ectodomain dimerization and molecular dynamics simulations demonstrated that this stable connection is mediated by the dimerization of the membrane-proximal IPT4 domains of Met.
While HGF binding to the Sema domain of Met is known to promote receptor association at the extracellular head region, the study uncovers a critical mechanism of Met activation: HGF not only facilitates head-to-head association but also drives the dimerization of the IPT4 domains, thereby stabilizing the Met dimer. This new understanding is pivotal for the development of targeted therapies in cancer treatment.
Implications for Future Research
Beyond elucidating this key activation mechanism of the Met receptor, this study presents a powerful strategy for investigating physiological protein complexes. By combining HS-AFM with other techniques, the dynamic structures of such complexes can be visualized at high spatiotemporal resolution. The integration of computational analysis offers significant potential for advancing our understanding of complex biological systems, particularly those involving transient or heterogeneous multiprotein assemblies challenging to resolve using conventional methods.
Conclusion
The implications of the findings regarding the HGF-Met interaction are far-reaching, especially within the context of cancer progression and tissue regeneration. The identification of this activation mechanism opens new avenues for targeted therapeutic strategies and provides a foundational understanding necessary for future explorations into receptor signaling.
Publication Details
Neval Yilmaz et al, Ligand Binding to the Membrane-Distal Domain of the Met Receptor Induces Dimerization at the Membrane-Proximal Domain, ACS Nano (2025).
Discussion