Alpha-Gal Syndrome: Involvement of Amblyomma americanum α-D-galactosidase and β-1,4 Galactosyltransferase enzymes in α-gal metabolism

Alpha-Gal Syndrome (AGS) is an IgE-mediated delayed-type hypersensitivity reaction to the oligosaccharide galactose--1,3-galactose (-gal) injected into humans from the lone star tick (Amblyomma americanum) bite. This study aims at the functional characterization of two tick enzymes, -D-galactosidase (ADGal) and -1,4 galactosyltransferase ({beta}-1,4GalT) in -gal metabolism. The ADGal enzyme cleaves terminal -galactose moieties from glycoproteins and glycolipids, whereas {beta}-1,4GalT transfers -galactose to a {beta}1,4 terminal linkage acceptor sugars: GlcNAc, Glc, and Xyl in various processes of glycoconjugate synthesis. An RNA interference approach was utilized to silence ADGal and {beta}-1,4GalT in Am. americanum to examine their functional role in -gal metabolism and AGS onset. Silencing of ADGal led to the significant down regulation of genes involved in galactose metabolism and transport in Am. americanum. Immunoblot and N-glycan analysis of the Am. americanum salivary glands showed a significant reduction in -gal levels in silenced tissues. However, there was no significant difference in the level of -gal in {beta}-1,4GalT silenced tick salivary glands. A basophil-activation test showed a decrease in the frequency of activated basophil by ADGal silenced salivary glands. These results provide an insight into the role of -D galactosidase & {beta}-1,4GalT in tick biology and the probable involvement in the onset of AGS.