Trypanosoma cruzi, the agent of Chagas' disease, an ailment characteri
zed by a progressive chronic fibrotic myocarditis and degeneration of
tissues that are innervated by the autonomic nervous system, is a vora
cious sialic acid eater from glycoconjugates of the surrounding medium
. This is accomplished through an active trans-sialidase residing on t
he surface membrane of the trypomastigote stage, which is the parasite
form that invades vertebrate cells. The existence of the enzyme was p
roposed and established only 7 years ago and yet a flood of informatio
n on the subject is already available. Transsialidase is able to rever
sibly transfer sialic acid alpha(2-->3)-linked to an external Galbeta
from the host cell surface sialoglycoconjugates to a terminal Galbeta
of an appropriate acceptor on the parasite surface. In the absence of
an acceptor, the enzyme acts as a hydrolase transferring sialic acid t
o water. Trans-sialidase belongs to a highly heterogeneous gene family
of surface molecules sharing with each other and with bacterial neura
minidases variable degrees of nucleotide sequence homology and common
motifs. It has been proposed that sialylation of the parasite surface
catalyzed by trans-sialidase is necessary for successful invasion of t
he host cell, but the evidence available is still indirect. Another fu
nction could be a protection from lysis by the alternative pathway of
complement while the parasite is circulating in the acute phase of the
disease.