A new clustering of antibody CDR loop conformations

Area of Science:

• Structural Biology
• Immunology
• Computational Biology

Background:

• Previous antibody complementarity-determining region (CDR) analyses relied on limited canonical conformations.
• The Chothia analysis (1997) identified a small number of CDR conformations, influencing antibody structure studies.

Purpose of the Study:

• To re-evaluate CDR loop conformations using a significantly larger and higher-quality structural dataset.
• To identify novel conformational clusters beyond the established canonical models.

Main Methods:

• Utilized over 300 nonredundant, high-resolution antibody structures.
• Employed a distance function based on directional statistics and affinity propagation clustering.
• Analyzed 28 CDR-length combinations across L1, L2, L3, H1, and H2 loops.

Main Results:

• Identified 72 distinct conformational clusters for non-H3 CDRs, surpassing the 20 CDR-lengths analyzed previously.
• 15 CDR-lengths showed multiple clusters, with 10 having only one canonical class in prior analyses.
• Approximately 85% of non-H3 CDR sequences could be assigned to a cluster based on gene source and sequence.

Conclusions:

• The current antibody structural data reveals greater CDR conformational diversity than previously recognized.
• The new classification based on extensive data enhances antibody structure prediction and design methodologies.
• Previous assumptions about H3 loop conformations based on specific residues were not fully supported by the expanded dataset.