Calcium-dependent conformational stability of modules 1 and 2 of human gelsolin

• Published in: Biochemical journal 2000-09, Vol.350 Pt 3 (3), p.873-881
• Main Authors: Zapun, A, Grammatyka, S, Déral, G, Vernet, T
• Format: Article
• Language: English
• Subjects: Calcium - metabolism; Chromatography, Gel; Gelsolin - chemistry; Gelsolin - isolation & purification; Gelsolin - metabolism; Humans; Models, Molecular; Protein Conformation; Recombinant Proteins - chemistry; Recombinant Proteins - isolation & purification; Recombinant Proteins - metabolism; Thermodynamics
• ISSN: 0264-6021; 1470-8728
• DOI: 10.1042/0264-6021:3500873

Gelsolin modulates the actin cytoskeleton in the cytoplasm and clears the circulation of stray filaments. In vitro, gelsolin cleaves, nucleates and caps actin filaments, activities that are calcium-dependent. Both cellular and secreted forms share a sequence of 730 residues comprising six homologous modules termed G1-G6. A disulphide bond is formed in secreted G2, whereas in the cytoplasm it remains reduced. A point mutation in G2 causes an amyloidosis with neurological, ophthalmological and dermatological symptoms. This mutation does not affect the cytoplasmic form, while the secreted form is proteolysed. As a first step towards understanding how gelsolin folds and functions in different cellular compartments, we have characterized at equilibrium the urea-induced unfolding of G1 and G2, with or without calcium and/or disulphide bond. G1 and G2 both exhibit two-state unfolding behaviour and are stabilized by calcium. The disulphide bond also contributes to the stability of G2. In the absence of Ca(2+) and disulphide bond, G2 adopts a non-native conformation, suggesting that folding of G2 in the cytoplasm relies on the presence of surrounding modules or other molecular partners.