Identification and evaluation of UL36 protein from Dermacentor silvarum salivary gland and its interaction with Anaplasma ovis VirB10

BACKGROUND: Anaplasma ovis is a gram-negative, tick-borne obligate intraerythrocytic pathogen, which causes ovine anaplasmosis in small ruminants worldwide. VirB10 of A. ovis is an integral component of the Type IV Secretion System (T4SS). The T4SS is used by bacteria to transfer DNA and/or proteins undeviatingly into the host cell to increase their virulence. To more thoroughly understand the interaction between A. ovis and Dermacentor silvarum, a vector containing the virb10 gene of A. ovis was used as a bait plasmid to screen interacting proteins from the cDNA library of the D. silvarum salivary gland using the yeast two-hybrid system. METHODS: The cDNA of the D. silvarum salivary gland was cloned into the pGADT7-SmaI vector (prey plasmid) to construct the yeast two-hybrid cDNA library. The virb10 gene was cloned into the pGBKT7 vector to generate a bait plasmid. Any gene auto-activation or toxicity effects in the yeast strain Y2HGold were excluded. The screening was performed by combining the bait and prey plasmids in yeast strains to identify positive preys. The positive preys were then sequenced, and the obtained sequences were subjected to further analyses using Gene Ontology, UniProt, SMART, and STRING. Additionally, the interaction between the bait and the prey was evaluated using the glutathione S-transferase (GST) pull-down assay. RESULTS: A total of two clones were obtained from the cDNA library using the yeast two-hybrid system, and the sequence analysis showed that both clones encoded the same large tegument protein, UL36. Furthermore, the proteins GST-UL36 and His-VirB10 were successfully expressed in vitro and the interaction between the two proteins was successfully demonstrated by the GST pull-down assay. CONCLUSIONS: To our knowledge, this study is the first to screen for D. silvarum salivary gland proteins that interact with A. ovis VirB10. The resulting candidate, UL36, is a multi-functional protein. Further investigations into the functionality of UL36 should be carried out, which might help in identifying novel prevention and treatment strategies for A. ovis infection. The present study provides a base for exploring and further understanding the interactions between A. ovis and D. silvarum.