Surface antigens of Paramecium primaurelia. Membrane-bound and soluble forms.
The surface antigens of Paramecium constitute a family of high molecular weight (ca 300 kD) iso-proteins whose alternative expression, adjusted to environmental conditions, involves both intergenic and interallelic exclusion. Since the surface antigen molecules had previously been shown to play a key role in the control of their own expression, it seemed important to compare the structural particularities of different surface antigens: the G and D antigens of P. primaurelia expressed at different temperatures, and which are coded by two unlinked loci. Here we demonstrate that in all cases a given surface antigen presents two biochemically distinct basic forms: a soluble form recovered from ethanolic extraction of whole cells, and a membrane-bound form recovered from ciliary membranes solubilized by detergent. The membrane-bound form differs from the soluble one by its mobility on SDS gels and by an electrophoretic mobility shift in the presence of anionic or cationic detergents. Furthermore, two 40-45 kD polypeptides sharing common determinants with soluble antigens were found exclusively in ethanolic extracts but not in ciliary membranes: the cross-reactivity of these light polypeptides with ethanol-extracted antigens could be demonstrated only after beta-mercaptoethanol treatment. Immunological comparisons between allelic and non-allelic soluble antigens demonstrate that allelic antigens share a great number of surface epitopes, most of which are not accessible in vivo, while non-allelic antigens appear to share essentially sequence-antigenic determinants. The significance of these results is discussed in relation to the mechanism of antigenic variation.
Capdeville
Y
Y
Deregnaucourt
C
C
Keller
A M
AM
D000483:Alleles; D000818:Animals; D000953:Antigens, Protozoan / Q000032:analysis* / Q000235:genetics; D000954:Antigens, Surface / Q000032:analysis / Q000235:genetics; D002462:Cell Membrane / Q000032:analysis; D002923:Cilia / Q000276:immunology; D003429:Cross Reactions; D000939:Epitopes / Q000276:immunology; D010247:Paramecium / Q000235:genetics / Q000276:immunology*; D012995:Solubility; D013696:Temperature
D000953:Antigens, Protozoan; D000954:Antigens, Surface; D000939:Epitopes