TheBabesia bovisMerozoite Surface Antigen 2 Locus Contains Four Tandemly Arranged and Expressed Genes Encoding Immunologically Distinct Proteins

• DOI: 10.1128/iai.70.7.3566-3575.2002
• Publication Date: 2002-07-27T10:09:14Z
• Authors: Monica Florin-Chr...; Carlos E. Suarez; Stephen A. Hines; Guy H. Palmer; Wendy C. Brown; Terry F. McElwain
• Keywords: 0301 basic medicine; 570; Base Sequence; Sequence Homology, Amino Acid; Transcription, Genetic; Genes, Protozoan; Molecular Sequence Data; Protozoan Proteins; Gene Expression; Membrane Proteins; Antigens, Protozoan; Sequence Analysis, DNA; DNA, Protozoan; Mice; 03 medical and health sciences; Tandem Repeat Sequences; Babesia bovis; Animals; Amino Acid Sequence; Fungal and Parasitic Infections; Conserved Sequence

ABSTRACTMembers of the variable merozoite surface antigen (vmsa) gene family ofBabesia bovisencode membrane proteins involved in erythrocyte invasion. In this study, we have identified and sequenced the complete 8.3-kb genomic locus containingmsa-2, a member of thevmsafamily, in the biologically cloned Mexico Mo7 strain. Four tandemly arranged copies ofmsa-2-related genes were found in the locus. The four genes, designatedmsa-2a1(which corresponds to the originally describedmsa-2gene),msa-2a2,msa-2b, andmsa-2c, were shown to be transcribed and expressed and encode proteins with open reading frames ranging in size from 266 (MSA-2c) to 317 (MSA-2a1) amino acids. MSA-2a1and -2a2are the most closely related of the four proteins (90% identity), differing by (i) the number of 24-amino-acid repeats that comprise a surface-exposed B-cell epitope and (ii) the presence of a 32-amino-acid area of recombination between MSA-2a2and -2b. In contrast,msa-2cis most closely related to the previously describedbabr 0.8gene in Australia strains ofB. bovis. Comparison of MSA-2 proteins in the Argentina R1A strain ofB. boviswith the Mexico Mo7 clone revealed a relatively high degree of conservation (83.6, 69.4, 79.1, and 88.7% amino acid identity for MSA-2a1, -2a2, -2b, and -2c, respectively), in contrast to the extensive MSA-1 sequence variation (52% identity) between the same two strains. Postinfection bovine immune serum contains antibodies that bound to each of the recombinant MSA-2 proteins. Blocking assays demonstrated the presence of unique B-cell epitopes in MSA-2a1, -2b, and -2c. The results support the evolution of themsa-2locus through at least two gene duplications, with selection for multiple related but antigenically distinct merozoite surface proteins.