RESUMEN
Amyloid light-chain (AL) amyloidosis is a protein-misfolding disease characterized by accumulation of immunoglobulin light chains (LCs) into amyloid fibrils. Dimerization of a full length or variable domain (VL ) of LC serves to stabilize the native state and prevent the formation of amyloid fibrils. We here analyzed the thermodynamic properties of dimerization and unfolding reactions by nonamyloidogenic VL from REI LC or its monomeric Y96K mutant using sedimentation velocity and circular dichroism. The data indicate that the equilibrium shifts to native dimerization for wild-type REI VL by elevating temperature due to the negative enthalpy change for dimer dissociation (-81.2 kJ·mol-1 ). The Y96K mutation did not affect the stability of the monomeric native state but increased amyloidogenicity. These results suggest that the heat-induced native homodimerization is the major factor preventing amyloid formation by wild-type REI VL . Heat-induced native oligomerization may be an efficient strategy to avoid the formation of misfolded aggregates particularly for thermostable proteins that are used at elevated temperatures under conditions where other proteins tend to misfold. DATABASE: Structural data are available in the Protein Data Bank under the accession numbers 5XP1 and 5XQY.
Asunto(s)
Amiloide/química , Cadenas Ligeras de Inmunoglobulina/química , Región Variable de Inmunoglobulina/química , Secuencia de Aminoácidos , Amiloide/genética , Amiloide/metabolismo , Clonación Molecular , Cristalografía por Rayos X , Escherichia coli/genética , Escherichia coli/metabolismo , Expresión Génica , Calor , Humanos , Cadenas Ligeras de Inmunoglobulina/genética , Cadenas Ligeras de Inmunoglobulina/metabolismo , Región Variable de Inmunoglobulina/genética , Región Variable de Inmunoglobulina/metabolismo , Cinética , Modelos Moleculares , Mutación , Pliegue de Proteína , Dominios y Motivos de Interacción de Proteínas , Multimerización de Proteína , Estabilidad Proteica , Estructura Secundaria de Proteína , Desplegamiento Proteico , Proteínas Recombinantes/química , Proteínas Recombinantes/genética , Proteínas Recombinantes/metabolismo , Dispersión del Ángulo Pequeño , Alineación de Secuencia , Homología de Secuencia de Aminoácido , Termodinámica , Difracción de Rayos XRESUMEN
Amyloid formation by immunoglobulin light chain (LC) proteins is associated with amyloid light chain (AL) amyloidosis. Destabilization of the native state of the variable domain of the LC (VL) is known to be one of the critical factors in promoting the formation of amyloid fibrils. However, determining the key residues involved in this destabilization remains challenging, because of the existence of a number of intrinsic sequence variations within VL. In this study, we identified the key residues for destabilization of the native state of amyloidogenic VL in the LC of BRE by analyzing the stability of chimeric mutants of BRE and REI VL; the latter immunoglobulin is not associated with AL amyloidosis. The results suggest that the surface-exposed residues N45 and D50 are the key residues in the destabilization of the native state of BRE VL. Point mutations at the corresponding residues in REI VL (K45N, E50D, and K45N/E50D) destabilized the native state and increased amyloidogenicity. However, the reverse mutations in BRE VL (N45K, D50E, and N45K/D50E) re-established the native state and decreased amyloidogenicity. Thus, analyses using chimeras and point mutants successfully elucidated the key residues involved in BRE VL destabilization and increased amyloidogenic propensity. These results also suggest that the modulation of surface properties of wild-type VL may improve their stability and prevent the formation of amyloid fibrils.
