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Recruitment of Light Chains by Homologous and Heterologous Fibrils Shows Distinctive Kinetic and Conformational Specificity.

Research paper by Luis Miguel LM Blancas-Mejia, Marina M Ramirez-Alvarado

Indexed on: 10 May '16Published on: 10 May '16Published in: Biochemistry



Abstract

Light chain amyloidosis is a protein misfolding disease where immunoglobulin light chains aggregate as insoluble fibrils that accumulate in extracellular deposits. Amyloid fibril formation in vitro has been described as a nucleation-polymerization, auto-catalytic reaction where nascent fibrils catalyze formation of new fibrils, recruiting soluble protein into the fibril. In this context, it is also established that preformed fibrils or "seeds" accelerate fibril formation. In some cases, seeds with substantially different sequence are able to accelerate the reaction albeit with a lower efficiency. In this work, we studied the recruitment and addition of monomers in the presence of seeds of five immunoglobulin light chain proteins, covering a broad range of protein stabilities and amyloidogenic properties. Our data reveal that in the presence of homologous or heterologous seeds, the fibril formation reactions become less stochastic compared to de novo reactions. The kinetics of the most amyloidogenic proteins (AL-T05 and AL-09) do not present significant changes in the presence of seeds. The amyloidogenic protein AL-103 presented fairly consistent acceleration with all seeds. In contrast, the less amyloidogenic proteins (AL-12 and κI) presented dramatic differential effects dependent of the kind of seed used. κI had a poor efficiency to elongate preformed fibrils. Together, these results indicate that fibril formation is kinetically determined by the conformation of the amyloidogenic precursor and modulated by the differential ability of each protein to either nucleate or elongate fibrils. We observe morphological and conformational properties of some seeds that do not favor elongation with some proteins, resulting in a delay in the reaction.