Localized deletion-insertion mutations: a major factor in the evolution of immunoglobulin structural variability

Area of Science:

• Immunogenetics
• Molecular immunology
• Protein sequence analysis

Background:

• Mouse immunoglobulin kappa (Vk) chains are crucial for antibody diversity.
• Understanding Vk chain sequence variation is key to antibody engineering.

Purpose of the Study:

• To analyze amino acid sequence variations in mouse Vk chains.
• To investigate the relationship between framework and antigen-binding regions.
• To explore the role of multigenic control and selection in Vk chain evolution.

Main Methods:

• Comparative analysis of new and published mouse Vk chain amino acid sequences.
• Examination of sequences from the N-terminus to Cys23 (framework loop) and Cys23 to Trp35 (complementarity region L1).

Main Results:

• Significant sequence heterogeneity was observed in the NH2-Cys23 region of BALB/c mouse Vk chains, pointing to multigenic control.
• Remarkable structural diversity in size and sequence was found in the L1 region.
• A strong correlation exists between NH2-Cys23 sequence and L1 size, with chains sharing similar NH2-Cys23 sequences exhibiting similar L1 sizes.
• Evidence suggests selection has favored Vk chains with size variations in the L1 region.

Conclusions:

• Multigenic control governs mouse Vk chain diversity.
• The L1 region's structural heterogeneity is linked to specific NH2-Cys23 sequences.
• Evolutionary selection appears to act on L1 size variations within this multigenic system.
• Mutational processes involving triplet insertions/deletions in L1 may drive the generation of novel functional genes.