The Critical Role of the Constant Region in Thermal Stability and Aggregation of Amyloidogenic Immunoglobulin Light Chain

• Published in: Biochemistry (Easton) Vol. 49; no. 45; pp. 9848 - 9857
• Main Authors: Klimtchuk, Elena S, Gursky, Olga, Patel, Rupesh S, Laporte, Kathryn L, Connors, Lawreen H, Skinner, Martha, Seldin, David C
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 16.11.2010
• Subjects: Amyloidosis - immunology; Base Sequence; Chromatography, High Pressure Liquid; Humans; Immunoglobulin Constant Regions - chemistry; Immunoglobulin Constant Regions - genetics; Immunoglobulin Light Chains - chemistry; Immunoglobulin Light Chains - genetics; Immunoglobulin Variable Region - chemistry; Immunoglobulin Variable Region - genetics; Kinetics; Models, Molecular; Myocardium - immunology; Protein Denaturation; Protein Renaturation; Protein Stability; Recombinant Proteins - chemistry; Thermodynamics
• ISSN: 0006-2960; 1520-4995; 1520-4995
• DOI: 10.1021/bi101351c

Light chain (LC) amyloidosis (AL) is a fatal disease in which immunoglobulin LC deposit as fibrils. Although the LC amyloid-forming propensity is attributed primarily to the variable region, fibrils also contain full-length LC comprised of variable-joining (VL) and constant (CL) regions. To assess the role of CL in fibrillogenesis, we compared the thermal stability of full-length LC and corresponding VL and CL fragments. Protein unfolding and aggregation were monitored by circular dichroism and light scattering. A full-length λ6 LC purified from urine of a patient with AL amyloidosis showed irreversible unfolding coupled to aggregation. The transition temperature decreased at slower heating rates, indicating kinetic effects. Next, we studied five recombinant λ6 proteins: full-length amyloidogenic LC, its VL, germline LC, germline VL, and CL. Amyloidogenic and germline proteins showed similar rank order of stability, VL < LC < CL; hence, in the full-length LC, VL destabilizes CL. Amyloidogenic proteins were less stable than their germline counterparts, suggesting that reduction in VL stability destabilizes the full-length LC. Thermal unfolding of the full-length amyloidogenic and germline LC required high activation energy and involved irreversible aggregation, yet the unfolding of the isolated VL and CL fragments was partially reversible. Therefore, compared to their fragments, full-length LCs are more likely to initiate aggregation during unfolding and provide a template for the VL deposition. The kinetic barrier for this aggregation is regulated by the stability of the VL region. This represents a paradigm shift in AL fibrillogenesis and suggests CL region as a potential therapeutic target.