Specific binding of human plasma high density lipoprotein (cruzin) to Trypanosoma cruzi

Binding of high density lipoprotein (HDL) to Trypanosoma cruzi was examined because of its ability to specifically inhibit the parasite's neuraminidase. 125I-Labeled HDL bound to live and glutaraldehyde-fixed parasites equally well either at 37 degrees C or at 4 degrees C. Binding was saturable and inhibited by unlabeled HDL but not by unrelated plasma proteins. Specificity of the T. cruzi-HDL interaction was confirmed using fluorescein labeled HDL which bound to T. cruzi but not to T. rangeli, a species whose neuraminidase is not inhibited by HDL. Binding of HDL to T. cruzi paralleled the neuraminidase activity exhibited by the parasite's different stages and strains. In agreement with this finding, Steck and Wallach analysis of the binding data showed that the number of HDL binding sites was greater in infective trypomastigotes and on strains with high neuraminidase activity. However, the association constant of the binding did not change within the various developmental forms and strains of T. cruzi, suggesting that HDL bound to the same receptor, presumably having neuraminidase activity.