GPIs of T. gondii associate with galectin-3. A, structures of T. gondii GPIs: GPIs I and II, (EtN-P)-Manα1–2Manα1–6(Glcα1–4GalNAcβ1–4)Manα1–4GlcNα-Ino-P-DAG; GPI III, (EtN-P)-Manα1–2Manα1–6(GalNAcβ1–4)Manα1–4GlcNα-Ino-P-DAG; GPIs IV and V, Manα1–2Manα1–6(Glcα1–4GalNAcβ1–4)Manα1–4GlcNα-Ino-P-DAG; and GPI VI, Manα1–2Manα1–6(GalNAcβ1–4)Manα1–4GlcNα-Ino-P-DAG. GPIs I and II, and GPIs IV and V differ in their diacylglycerol composition with palmitic and stearic acids as predominant fatty acids. EtN, ethanolamine, P, phosphate; Man, mannose; Glc, glucose; GalNAc, acetylgalactosamine; GlcN, glucosamine; Ino, inositol; DAG, diacylglycerol. B–E, SPR analysis of the interaction of immobilized galectin-3 with the six different T. gondii GPIs (I–VI) at 3 μm (B); different concentrations of T. gondii GPI III with Scatchard plot analysis of the sensorgram data shown in the inset (slope = −127.4) (C); GPI III at 3 μm in the presence of 30 mm lactose (D); or laminin at 10 μg/ml (E). Results are expressed as RU (proportional to the quantity of molecules) after the subtraction of the nonspecific binding. Sensorgrams are representative of independent experiments with similar results.