Effect of the ionic environment on the molecular structure of bacteriophage SPP1 portal protein.
Bacteriophage SPP1 portal protein is a large cyclical homo-oligomer composed of 13 subunits. The solution structure and assembly behavior of this protein with high-point rotational symmetry was characterized. The purified protein was present as a monodisperse population of 13-mers, named gp6H, at univalent salt concentrations in the hundred millimolar range (>/= 250 mM NaCl) or in the presence of bivalent cations in the millimolar range (>/= 5 mM MgCl2). Gp6H had a slightly higher sedimentation coefficient, a smaller shape-dependent frictional ratio, and a higher rate of intersubunit cross-linking in the presence of magnesium than in its absence. In the absence of bivalent cations and at univalent salt concentrations below 250 mM, the 13-mer molecules dissociated partially into stable monomers, named gp6L. The monomer had a somewhat different shape from the subunit present in the 13-mer, but maintained a defined tertiary structure. The association-dissociation equilibrium was mainly between the monomer and the 13-mer with a minor population of intermediate oligomers. Their interconversion was strongly influenced by the ionic environment. Under physiological conditions, the concentration of Mg2+ found in the Bacillus subtilis cytoplasm (10-50 mM) probably promotes complete association of gp6 into 13-mer rings with a compact conformation.
Jekow
P
P
Max Planck Institut für Molekulare Genetik, Berlin, Germany.
Behlke
J
J
Tichelaar
W
W
Lurz
R
R
Regalla
M
M
Hinrichs
W
W
Tavares
P
P
D017103:Bacillus Phages / Q000737:chemistry / Q000235:genetics; D002413:Cations, Divalent; D002499:Centrifugation, Density Gradient; D003432:Cross-Linking Reagents; D004355:Drug Stability; D005976:Glutaral; D008854:Microscopy, Electron; D008970:Molecular Weight; D009994:Osmolar Concentration; D011487:Protein Conformation; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification; D012996:Solutions; D014764:Viral Proteins / Q000737:chemistry* / Q000235:genetics / Q000302:isolation & purification
D002413:Cations, Divalent; D003432:Cross-Linking Reagents; D011994:Recombinant Proteins; D012996:Solutions; D014764:Viral Proteins; C115880:portal protein, Bacteriophage SPP1; D005976:Glutaral