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 TFRR1 drug-resistant mutant was analyzed with the aid of an influenza C virus strain, lectin, enzymatic treatment, and f low cytofluorimetry analysis probed with fluorescein isothiocyanate-labeled (FITC) lectins. 9-O-Acetyl-N-acetyl neuraminic acid (Neu5,9Ac(2)) structur es mediate influenza C virus cell-binding. The SA alpha 2,3Gal and SA alpha 2,6Gal sequences are specifically recognized by Maackia amurensis (MAA) an d Sambucus nigra (SNA) lectins, respectively. On the basis of these paramet ers the TFRR1 mutant strain of C. fasciculata was found to contain exposed sialoglycoconjugates bearing Neu5,9Ac2 surface structures. After the remova l 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-galact ose. The bond involves SA alpha 2,6Gal and SA alpha 2,3Gal linkages as sugg ested by the use of FITC-SNA and FITC-MAA lectins, respectively. Both SA al pha 2,3Gal and SA alpha 2,6Gal sequences were preferentially expressed by t he TFRR1 mutant. The SA alpha 2,6 linkage markedly predominated. In the TFR R1 mutant, but not in wild-type cells, two distinct populations of cells we re distinguished by reactivity with FITC-SNA, one of which was enriched wit h surface SA alpha 2,6Gal sequences. These diverse findings suggest that si aloglycoconjugate structures present on the flagellate surface may be assoc iated with mutation and the cell growth cycle in C. fasciculata.