A human germ line antibody light chain with hydrolytic properties associated with multimerization status

Area of Science:

• Immunology
• Biochemistry
• Structural Biology

Background:

• Antibodies can possess nucleophilic or catalytic properties, often encoded in germ line genes.
• Hydrolytic activity has been linked to the variable light (V) regions of antibodies.

Purpose of the Study:

• To analyze germ line light chain proteins as a basis for affinity maturation into reactive antibodies.
• To characterize the hydrolytic, nucleophilic, and structural properties of the germ line A18b light chain.

Main Methods:

• Production and purification of the germ line A18b light chain to >99% purity.
• Assays to determine hydrolytic activity against peptide and protein substrates.
• Binding assays using a fluorophosphonate probe to assess nucleophilic activity.
• Site-directed mutagenesis of putative catalytic residues to evaluate their role in activity.

Main Results:

• The purified A18b light chain demonstrated hydrolytic activity against aminomethylcoumarin-peptide and larger protein substrates.
• The light chain also exhibited nucleophilic activity, confirmed by binding to a fluorophosphonate probe.
• Mutation of key residues abolished activity in the tetrameric form but not the dimeric form, suggesting differential roles based on quaternary structure.

Conclusions:

• The germ line A18b light chain possesses inherent hydrolytic and nucleophilic biochemical properties.
• These findings establish a foundation for understanding the structure-function relationships of germ line antibodies and their potential for developing catalytic antibodies.