Conformational stability of a human cryoglobulin

Area of Science:

• Biochemistry
• Immunology
• Protein Chemistry

Background:

• Human cryo-immunoglobulin (cryo-IgG) self-associates to form visible gels.
• Understanding the conformational stability of macromolecular interfaces is crucial for cryo-IgG self-association.
• Alkaline conditions can induce conformational changes in proteins.

Purpose of the Study:

• To investigate the conformational stability of human cryo-IgG and a monoclonal IgG (Hy IgG) in alkaline media.
• To determine the impact of pH on cryo-IgG self-association and gel formation.
• To compare the structural behavior of cryo-IgG and Hy IgG.

Main Methods:

• Analytical ultracentrifugation to assess gross conformational changes.
• Fluorescence characteristics, tyrosine ionization, and H+ titration to evaluate localized conformational changes.
• Comparative analysis of cryo-IgG and Hy IgG under varying alkaline pH conditions.

Main Results:

• Major conformational transitions occurred at pH 11.4 for cryo-IgG and pH 11.7 for Hy IgG.
• Protein fragmentation and loss of gel formation capacity were observed beyond transition pH.
• Cryo-IgG renatured up to pH 11.4 retained gel-forming ability despite irreversible local changes.
• Distinct differences in tyrosine residue accessibility were noted between cryo-IgG and Hy IgG.

Conclusions:

• Cryo-IgG self-association and gel formation are sensitive to pH-induced conformational changes.
• While alkaline conditions can disrupt cryo-IgG structure, some renaturation and gel formation capacity can be restored.
• Differences in tyrosine residue exposure highlight unique structural properties of cryo-IgG compared to Hy IgG.