Structure and conformational variability of the HER2-trastuzumab-pertuzumab complex

Area of Science:

• Structural Biology
• Cryo-Electron Microscopy (Cryo-EM)
• Cancer Therapeutics

Background:

• Antibody-antigen complexes are challenging for structure prediction.
• Human epidermal growth factor receptor 2 (HER2) is a key target in cancer therapy.
• Understanding the structural basis of antibody binding to HER2 is crucial for drug development.

Purpose of the Study:

• To determine the detailed structure of the complex between HER2 and two therapeutic antibodies, pertuzumab and trastuzumab (HTP).
• To investigate the role of continuous conformational heterogeneity in cryo-EM data processing.
• To identify structural features contributing to the synergistic anticancer effect of the antibodies.

Main Methods:

• Single particle analysis using cryogenic transmission electron microscopy (cryo-EM).
• Utilized ultra-thin continuous carbon grids for optimal data collection.
• Analyzed data processing software for handling conformational heterogeneity.

Main Results:

• Obtained a detailed structure of the HTP ternary complex, offering a more comprehensive view than previously available.
• Identified a previously overlooked loop in HER2 domain IV potentially involved in trastuzumab binding and HER2 dimerization.
• Demonstrated the feasibility of cryo-EM for small protein complexes (162 kDa) using advanced techniques.

Conclusions:

• The identified HER2 loop may explain the synergistic anticancer effect of pertuzumab and trastuzumab.
• The flexibility of the HTP complex reflects HER2 signaling regulation and antibody inhibition.
• The study provides a valuable dataset for developing cryo-EM software to address conformational heterogeneity.