Different crystal packing in Fab-protein L semi-disordered peptide complex

Area of Science:

• Structural Biology
• Biophysics
• Crystallography

Background:

• Proteins and peptides with intrinsic disorder pose significant challenges for structural determination via protein crystallization.
• Disordered regions can adopt multiple conformations, complicating the acquisition of well-defined structural data.

Purpose of the Study:

• To crystallize a complex involving a Hepatitis C virus (HCV) peptide and a murine monoclonal antibody (19D9D6).
• To investigate the utility of a bacterial protein L domain (PpL) in facilitating the crystallization of poorly structured antigens.
• To explore the potential of the resulting crystal lattice as a scaffold for crystallizing other peptide-tagged proteins.

Main Methods:

• Co-crystallization of a murine monoclonal antibody (19D9D6) with a synthetic peptide (HCV core protein residues 1-45).
• Inclusion of a single immunoglobulin-binding domain of protein L (PpL) to aid complex formation and crystallization.
• Analysis of crystal structures obtained in different space groups, focusing on lattice variations and peptide ordering.

Main Results:

• Successful crystallization of the trimolecular complex (antibody-peptide-PpL).
• Crystals formed in different space groups with varying cavity sizes accommodating the peptide.
• A larger cavity within the crystal lattice correlated with a more ordered peptide structure.
• The crystal lattice exhibited preserved contacts and overall structure despite variations in cavity size.

Conclusions:

• The bacterial protein L domain (PpL) can facilitate the crystallization of antibody-antigen complexes involving semi-disordered peptides.
• The crystal lattice structure offers a potential scaffold system for crystallizing peptide-tagged proteins.
• The size of the accommodating cavity influences the degree of order observed in the crystallized peptide.