RESUMEN
Glycosylation is one of the major post-translational modifications in eukaryotic cells and has been reported to affect the amyloid fibril formation in several amyloidogenic proteins and peptides. In this study, we expressed a Vλ6 light chain mutant, Wil, which is an amyloidogenic mutant in AL amyloidosis, by the yeast Pichia pastoris. After separation by cation exchange chromatography, we obtained the O-glycosylated and non-glycosylated Wil mutants in high yield. The structures of these Wil mutants were identical except with respect to glycosylation, and the stabilities were also identical. On the other hand, the O-glycosylation retarded the amyloid fibril formation in a sugar size-dependent manner. From these results, we discussed the role of covalently attached glycan in the retardation of amyloid fibril formation.
Asunto(s)
Amiloide/química , Región Variable de Inmunoglobulina/química , Cadenas lambda de Inmunoglobulina/química , Mutación , Procesamiento Proteico-Postraduccional , Amiloide/genética , Amiloide/metabolismo , Glicosilación , Humanos , Región Variable de Inmunoglobulina/genética , Región Variable de Inmunoglobulina/metabolismo , Cadenas lambda de Inmunoglobulina/genética , Cadenas lambda de Inmunoglobulina/metabolismo , Multimerización de Proteína , Estabilidad Proteica , SaccharomycetalesRESUMEN
BACKGROUND: Light chains are abnormally overexpressed from disordered monoclonal B-cells and form amyloid fibrils, which are then deposited on the affected organ, leading to a form of systemic amyloidosis known as AL (Amyloid Light chain) amyloidosis. A green tea catechin, epigallocatechin-3-O-gallate (EGCG), which is thought to inhibit various amyloidoses, is a potent inhibitor of amyloid fibril formation in AL amyloidosis. METHODS: An amyloidogenic variable domain in λ6 light chain mutant, Wil was incubated in the presence of EGCG. The incubation products were analyzed by SDS-PAGE and reverse-phase HPLC. The interaction between Wil and EGCG was observed by using NMR and tryptophan fluorescence. RESULTS: EGCG inhibited the amyloid fibril formation of Wil at pHâ¯7.5 and 42⯰C. Under these conditions, most Wil populations were in the unfolded state and several chemical reactions, i.e., oxidation and/or covalent bond oligomerization could be induced by auto-oxidated EGCG. Moreover, we found that EGCG bound to the unfolded state of Wil with higher affinity (Kdâ¯=â¯7⯵M). CONCLUSIONS: Inhibition of amyloid fibril formation of Wil was caused by 1) EGCG binding to unfolded state rather than folded state and 2) chemical modifications of Wil by auto oxidation of EGCG. GENERAL SIGNIFICANCE: In the competitive formation of amyloid fibrils and off-pathway oligomers, EGCG produces the latter immediately after it preferentially binds to the unfolded state. It may be general mechanism of EGCG inhibition for amyloidosis.