Characterization of the variable merozoite surface antigen (VMSA) gene family of Babesia orientalis

Due to its wide presence in apicomplexan parasites as well as high polymorphism and antigenic diversity, the variable merozoite surface antigen (VMSA) family in Babesia sp. has attracted increasing attention of researchers. Here, all the reported VMSA genes of Babesia spp. were obtained from GenBank, and multiple alignments were performed by using conserved regions to blast the Babesia orientalis genome database (unpublished data). Five MSA genes (named MSA-2a1, MSA-2a2, MSA-2c1, MSA-1, and MSA-2c2, respectively) were identified, sequenced, and cloned from B. orientalis, which were shown to encode proteins with open reading frames ranging in size from 266 (MSA-2c1) to 317 (MSA-1) amino acids. All the five proteins contain an MSA-2c superfamily conserved domain, with an identical signal peptide and glycosyl phosphatidyl inositol (GPI)-anchor for each of them. The five proteins were also predicted to contain B cell epitopes, with only three for BoMSA-2c1, the smallest protein in the BoVMSA family, while at least six for each of the others. Notably, BoMSA-2a1 has 2 identical copies, a specific phenomenon only present in B. orientalis. This research has determined the MSA genes of B. orientalis and provides a genetic basis for further research of functional genes in B. orientalis.