Structure-function analysis of empasiprubart, a calcium- and pH-dependent clinical phase complement C2 blocking...

Area of Science:

• Immunology
• Structural Biology
• Biochemistry

Background:

• Empasiprubart (ARGX-117) is a humanized recycling antibody targeting complement component C2.
• It blocks classical and lectin complement pathways by preventing C2-C4b binding.
• The antibody's pH-dependent release mechanism and prolonged half-life are crucial for its function.

Purpose of the Study:

• To elucidate the molecular mechanism behind empasiprubart's pH-dependent binding and release from complement component C2.
• To provide a structural rationale for the antibody's unique properties and recycling capacity.
• To understand the role of framework residues in antibody complementarity-determining region (CDR) function.

Main Methods:

• X-ray crystallography of the empasiprubart fragment antigen-binding (Fab) complexed to a C2 fragment.
• Analysis of structural data to understand intramolecular interactions and pH-dependent effects.
• Investigation of the interplay between antibody framework residues and CDRs.

Main Results:

• The crystal structure reveals empasiprubart binds to the C2 CCP2 domain in a calcium- and pH-dependent manner.
• pH-dependent target release is mediated by subtle intramolecular CDR destabilization, not direct interface modulation.
• Framework residues play a pivotal role in orchestrating CDR function for specific target binding.

Conclusions:

• Empasiprubart's unique properties stem from a pH-dependent mechanism involving CDR destabilization.
• The study highlights the critical role of antibody framework residues in modulating CDR function.
• These findings enhance the understanding of empasiprubart's mode of action and antibody engineering principles.