Diversity and functional characterisation of the predicted ATAQ complex from Rhipicephalus microplus

Abstract

Rhipicephalus microplus is an economically important tick species affecting the cattle industry through direct and indirect effects. Since current tick control relies heavily on chemical acaricides, an increased incidence in tick populations resistant to all classes of acaricides have been observed in recent years. Alternative complementary approaches, such as tick vaccines, have been explored, and some of the most successful experimental tick vaccines employ the R. microplus midgut antigen, Bm86. However, variable efficacy in the field and limited cross-species protection has been observed, likely due to inter- and intra-species variation in the Bm86 antigen. ATAQ proteins are Bm86 orthologues with a higher level of sequence conservation compared to the Bm86 vaccine antigen. Towards the development of an ATAQ-based R. microplus control strategy (i.e. vaccine or small drug targets), our group has identified the partial sequences for two ATAQ-interacting protein partners, i.e. an aldehyde dehydrogenase (ALDH) and a retinol dehydrogenase (RDH), respectively. ATAQ proteins are predicted to have a transmembrane domain and localise to the plasma membrane. The potential for ATAQ to interact with ALDH and RDH, which may localise differently, underscores the importance of studying its subcellular localisation. This project sought to determine the subcellular localisation of ATAQ by using the baculovirus expression system to express BmATAQ and BmATAQ eGFP-chimeras. It is shown for the first time that BmATAQ localises to the plasma membrane, endomembrane system and possibly co-localises with the mitochondrion. This in contrast to Bm86 that only occurs on the plasma membrane of tick gut cells. In conclusion, these results may point towards a possible BmATAQ, ALDH and RDH complex which provide some insight into its biological function.