Molecular cloning and characterization of a glycine-like receptor gene from the cattle tick Rhipicephalus (Boophilus) microplus (Acari: Ixodidae).
Bottom Line: The polypeptide also contains the PAR motif, which is important for forming anion channels, and a conserved glycine residue at the third transmembrane domain, which is essential for high ivermectin sensitivity.PCR analyses showed that RmGlyR is expressed at egg, larval and adult developmental stages.Our findings suggest that the deduced receptor is an additional molecular target to ivermectin and it might be involved in ivermectin resistance in R. microplus.
Affiliation: Centro de Investigación y Asistencia en Tecnología y Diseño del Estado de Jalisco, AC, Av. Normalistas 800, Col. Colinas de la Normal, 44270 Guadalajara, Jalisco, México.Show MeSH
Mentions: Hibbs and Gouaux  recently solved the crystal structure of the Caenorhabditis elegans αGluCl complexed with IVM. The IVM binding site is formed at the interface of two adjacent subunits in the transmembrane domain of the receptor. Given the high structural similarity among GluCls and GlyRs, it is possible that IVM binds in a common location in the GluCl and GlyR. Lynagh and Lynch  showed that a glycine residue at the TM3 transmembrane domain location is essential for high IVM sensitivity in both glycine- and glutamate-gated Cys-loop receptors. We compared the amino acid sequences of the three LGICs reported so far in R. microplus and surprisingly detected a conserved TM3-Glycine residue in the three receptors (Fig. 5, shaded in turquoise). The presence of this glycine residue would predict high IVM sensitivity of these LGICs, in contrast to the human GlyRs (Fig. 3). We also found that these receptors possess the PAR motif before the transmembrane region 2 (TM2), which is important for forming anion channels (Fig. 5) . The results from the protein sequence homology analyses and other bioinformatic predictions indicate that we have identified the R. microplus gene ortholog for GlyR. Taken together, these findings point out GABA, GluCl, and GlyR as being the molecular targets for IVM in R. microplus. This may well explain the susceptibility of the tick to this class of acaricide, although we do not discard the fact that more targeted LGICs may exist. The functional characterization of these receptors is required to enhance our understanding of the mechanism of action of IVM, which will facilitate the management of macrocyclic lactone resistance in R. microplus.Figure 5.
Affiliation: Centro de Investigación y Asistencia en Tecnología y Diseño del Estado de Jalisco, AC, Av. Normalistas 800, Col. Colinas de la Normal, 44270 Guadalajara, Jalisco, México.