Evidence for sodium dodecyl sulfate/protein complexes adopting a necklace structure.
Structural analysis by cryo-electron microscopy and small-angle X-ray scattering of ten sodium dodecyl sulfate/protein complexes in 25 mM Tris/HCl, 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 (approximately 6.2 nm), slightly larger than pure SDS micelles (approximately 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 SDS/protein 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.
Samsó
M
M
Biological Spectroscopy and Imaging Group, CCL, Daresbury Laboratory, Warrington, England.
Daban
J R
JR
Hansen
S
S
Jones
G R
GR
D005615:Freezing; D008854:Microscopy, Electron / Q000379:methods; D008956:Models, Chemical; D008970:Molecular Weight; D011506:Proteins / Q000737:chemistry*; D012542:Scattering, Radiation; D012967:Sodium Dodecyl Sulfate / Q000737:chemistry*; D012996:Solutions; D014965:X-Rays
D011506:Proteins; D012996:Solutions; D012967:Sodium Dodecyl Sulfate