Antibody CDR loops as ensembles in solution vs. canonical clusters from X-ray structures

Area of Science:

• Biochemistry
• Structural Biology
• Immunology

Background:

• Antibodies are increasingly important therapeutics, necessitating detailed structural and functional characterization.
• Complementarity-determining regions (CDRs) are key to antibody binding properties.
• Current models classify CDR loops into a limited set of static conformations, potentially oversimplifying their behavior.

Purpose of the Study:

• To present a kinetic classification of complementarity-determining region (CDR) loop structures in solution.
• To investigate the dynamic nature of CDR loop conformations beyond static canonical structures.
• To provide a new paradigm for antibody structure-based design and engineering.

Main Methods:

• Molecular dynamics simulations were employed.
• Experimental structural information was integrated with simulations.
• Kinetic analysis, including Perron cluster analysis (PCCA) and time-lagged independent component analysis (tICA), was used.

Main Results:

• All CDR loops, regardless of length or sequence, exhibit conformational transitions on micro- to millisecond timescales.
• Dominant solution structures and transitions between canonical clusters were identified.
• Canonical cluster medians were found to belong to the same kinetic minimum, revealing a dynamic ensemble.

Conclusions:

• CDR loop structures exist as dynamic conformational ensembles in solution, challenging the static canonical model.
• Understanding these dynamic ensembles is essential for advanced antibody design and engineering.
• This kinetic perspective offers a new paradigm for developing novel antibody therapeutics.