Cell-surface sialoglycoconjugate structures in wild-type and mutant Crithidia fasciculata

The cell-surface expression of sialoglycoconjugate structures in wild-type Crithidia fasciculata and its TFR(R1) drug-resistant mutant was analyzed with the aid of an influenza C virus strain, lectin, enzymatic treatment, and flow cytofluorimetry analysis probed with fluorescein isothiocyanate-labeled (FITC) lectins. 9-O-Acetyl-N-acetyl neuraminic acid (Neu5,9Ac2) structures mediate influenza C virus cell-binding. The SAalpha2,3Gal and SAalpha2,6Gal sequences are specifically recognized by Maackia amurensis (MAA) and Sambucus nigra (SNA) lectins, respectively. On the basis of these parameters the TFR(R1) mutant strain of C. fasciculata was found to contain exposed sialoglycoconjugates bearing Neu5,9Ac2 surface structures. After the removal of sialic acid residues by neuraminidase activity the marked increases in PNA (peanut agglutinin)-mediated agglutinating activity showed that those acidic units on C. fasciculata cells were glycosidically linked to D-galactose. The bond involves SAalpha2,6Gal and SAalpha2,3Gal linkages as suggested by the use of FITC-SNA and FITC-MAA lectins, respectively. Both SAalpha2,3Gal and SAalpha2,6Gal sequences were preferentially expressed by the TFR(R1) mutant. The SAalpha2,6 linkage markedly predominated. In the TFR(R1) mutant, but not in wild-type cells, two distinct populations of cells were distinguished by reactivity with FITC-SNA, one of which was enriched with surface SAalpha2,6Gal sequences. These diverse findings suggest that sialoglycoconjugate structures present on the flagellate surface may be associated with mutation and the cell growth cycle in C. fasciculata.