Disulfide bond involvement in the maintenance of the cryptic nature of the cross-reacting determinant of metacyclic forms of Trypanosoma congolense

• Published in: Biochemistry (Easton) Vol. 28; no. 13; pp. 5415 - 5421
• Main Authors: Fish, Wallace R, Muriuki, Cecilia W, Muthiani, Anthony M, Grab, Dennis J, Lonsdale-Eccles, John D
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 27.06.1989
• Subjects: 550201 - Biochemistry- Tracer Techniques; ANIMALS; Antigen-Antibody Reactions; Antigenic determinants, haptens, artificial antigens; Antigens; BASIC BIOLOGICAL SCIENCES; Biological and medical sciences; Blotting, Western; CARBOXYLIC ACIDS; CHEMICAL BONDS; Cross Reactions; disulfide bonds; Disulfides - analysis; ELECTROPHORESIS; Electrophoresis, Polyacrylamide Gel; Epitopes - analysis; Fundamental and applied biological sciences. Psychology; Fundamental immunology; GLYCOPROTEINS; HYDROGEN COMPOUNDS; Immunoglobulin G; INVERTEBRATES; MASTIGOPHORA; METABOLISM; MICROORGANISMS; Molecular immunology; MOLECULAR STRUCTURE; Molecular Weight; MONOCARBOXYLIC ACIDS; Myristic Acid; Myristic Acids - metabolism; ORGANIC ACIDS; ORGANIC COMPOUNDS; PARASITES; PROTEINS; PROTOZOA; TETRADECANOIC ACID; TRITIUM COMPOUNDS; TRYPANOSOMA; Trypanosoma congolense - immunology; Variant Surface Glycoproteins, Trypanosoma - immunology; Protozoa; Antigenic determinant; Disulfide bond; Trypanosoma congolense; Rhizoflagellata; Glycoproteins; Cell surface
• ISSN: 0006-2960; 1520-4995
• DOI: 10.1021/bi00439a015

The variable surface glycoprotein (VSG) of African trypanosomes possesses a 1,2-dimyristoylglycosylphosphatidylinositol at the carboxy terminus. Cleavage of the 1,2-dimyristoylglycerol (1,2-DMG) moiety from the VSG reportedly results in a higher apparent molecular mass and an increased binding of antibodies against the "cross-reacting determinant" (CRD), a cryptic epitope present on most VSGs. Using metacyclic forms of Trypanosoma congolense, we show that the processes involved are more complex than heretofore presumed and that the removal of the 1,2-DMG moiety may not be necessary for binding of anti-CRD antibodies (RxCRD). Among other findings, we observe the following: (1) in sonicated samples of trypanosomes metabolically labeled with [3H]myristate, the binding of RxCRD on Western blots is coincident with bands containing labeled (membrane form) VSGs; (2) disulfide reduction of trypanosome sonicates suffices to promote RxCRD binding in the presence or absence of inhibitors of a glycosylphosphatidylinositol-specific phospholipase C; (3) trypanosomes directly solubilized in detergents show quantitative and qualitative differences in RxCRD binding which depend upon the detergent used and the order of addition of disulfide reducing agents. We conclude that the binding of RxCRD to T. congolense metacyclic VSGs depends upon the degree of unfolding of the molecule and is clearly a complex, multistep process in which structural changes and disulfide reduction play pivotal roles.