Multimerization and Aggregation of Native-State Insulin: Effect of Zinc

• Published in: Langmuir 2012-01, Vol.28 (1), p.579-586
• Main Authors: Xu, Yisheng, Yan, Yunfeng, Seeman, Daniel, Sun, Lianhong, Dubin, Paul L
• Format: Article
• Language: English
• Subjects: Biological Interfaces: Biocolloids, Biomolecular and Biomimetic Materials; Chemistry; Chromatography, Gel; Exact sciences and technology; General and physical chemistry; Insulin - chemistry; Nephelometry and Turbidimetry; Polymers - chemistry; Zinc - chemistry
• ISSN: 0743-7463; 1520-5827
• DOI: 10.1021/la202902a

The aggregation of insulin is complicated by the coexistence of various multimers, especially in the presence of Zn2+. Most investigations of insulin multimerization tend to overlook aggregation kinetics, while studies of insulin aggregation generally pay little attention to multimerization. A clear understanding of the starting multimer state of insulin is necessary for the elucidation of its aggregation mechanism. In this work, the native-state aggregation of insulin as either the Zn–insulin hexamer or the Zn-free dimer was studied by turbidimetry and dynamic light scattering, at low ionic strength and pH near pI. The two states were achieved by varying the Zn2+ content of insulin at low concentrations, in accordance with size-exclusion chromatography results and literature findings ( Tantipolphan R. ; Romeijn S. ; Engelsman J. d. ; Torosantucci R. ; Rasmussen T. ; Jiskoot W. J. Pharm. Biomed. 2010, 52, 195 ). The much greater aggregation rate and limiting turbidity (τ∞) for the Zn–insulin hexamer relative to the Zn-free dimer was explained by their different aggregation mechanisms. Sequential first-order kinetic regimes and the concentration dependence of τ∞ for the Zn–insulin hexamer indicate a nucleation and growth mechanism, as proposed by Wang and Kurganov ( Wang K. ; Kurganov B. I. Biophys. Chem. 2003, 106, 97 ). The pure second-order process for the Zn-free dimer suggests isodesmic aggregation, consistent with the literature. The aggregation behavior at an intermediate Zn2+ concentration appears to be the sum of the two processes.