Evidence for Sodium Dodecyl Sulfate/Protein Complexes Adopting a Necklace Structure

Abstract

Structural analysis by cryo-electron microscopy and small-angle X-ray scattering of ten sodium dodecyl sulfate/protein complexes in 25 mM Tris/HCI, 0.192 M glycine, pH 8.3, showed necklace-like structures of spherical micelles dispersed along the unfolded peptide chain. The micelles of most SDS/protein complexes had a constant diameter (= 6.2 nm), slightly larger than pure SDS micelles (-5.7 nm), all micelles possessing a degree of surface roughness. The micelle-associated polypeptide is mostly situated at the interface of the sulfate head groups and hydrocarbon core, intruding into the core rather than outward from the surface. Proteins with a molecular mass less than about 20 kDa formed complexes with a single SDS micelle. Multi-micellar SDSIprotein complexes had centre-to-centre intermicellar distances in the range 7.0-12.0 nm. Our findings on the constancy of micellar size, number of micelles/complex, and the relationship between the degree of occupancy of micelles and a polypeptide's molecular mass, have enabled us to speculate on the correlation between the electrophoretic mobility of a polypeptide in SDS/PAGE and its molecular mass. The anomalous electrophoretic behaviour observed for the sodium dodecyl sulfate/histone H5 complex is accounted for by the large micelle of its complex.

Polyacrylamide gel electrophoresis followed by sodium dodecyl sulfate gradient polyacrylamide gel electrophoresis for the study of the dimer to monomer transition of human transthyretin

“…The melting of the native protein structure at elevated temperature is followed by a complex association between the unfolded protein and SDS upon cooling. As shown by Samso et al [15] the resulting products appear to have a necklace structure of micelles 6.2 nm in diameter with a center to center distance of 7-12 nm. A single micelle could contain polypeptides with variable masses of up to some 20 kDa.…”

Creaming and Rheology of Oil-in-Water Emulsions Containing Sodium Dodecyl Sulfate and Sodium Caseinate

“…It seems that the presence of caseinate may be interferring with the depletion mechanism. It is known that SDS micelles can bind extensively onto various proteins, forming necklace-shaped complexes (25,26), and that these cooperative interactions do occur in aqueous solutions of casein + SDS (27). If similar mixed entities are formed in the emulsion aqueous phase between caseinate and SDS, then some surfactant molecules could be trapped in the casein self-assembled structure, effectively reducing the number of depletion-inducing free SDS micelles.…”

Denaturation of MM-creatine kinase by sodium dodecyl sulfate

“…Recent studies have demonstrated that proteins with molecular masses of less than 20 kDa form unimicellar complexes with a diameter of approximately 5.7-6.2nm (Samso et al, 1995) or 7-8 nm (Ibel et al, 1990). Higher molecular mass proteins form complexes which have two micelles and a length ranging from 13 to 18nm.…”

“…More ,recently a "flexible helix model" in which the interaction between SDS and protein involves the sulfate heads of SDS and the NH group of the peptide bonds was suggested by Lundahl et al (1986). This important prediction concerning the SDS-protein interaction was also supported by neutron or X-ray scattering experiments and it was subsequently proposed that these complexes could more accurately be described as a "proteindecorated micelle structure" (Ibel et al, 1990(Ibel et al, , 1994 or a "necklace structure" (Samso et al, 1995). We have studied the effects of SDS on the structure of MM-creatine kinase from rabbit muscle.…”