Nomenclature, classification, and in-silico structural analysis of MSP1a variants of Anaplasma marginale

Bovine anaplasmosis, caused by the tick-borne rickettsial pathogen Anaplasma marginale , is a significant threat to livestock health and productivity. The major surface protein 1a (MSP1a) is a widely used molecular marker for characterizing strain diversity, due to its variable N-terminal tandem repeats. In this study, we analyzed and updated the nomenclature classification of 157 A. marginale MSP1a sequences submitted to NCBI between 2013 and 2023, following the research by Cabezas-Cruz in 2013. We identified and classified 189 unique tandem repeats, reported their tick-transmissibility, predicted their secondary structures and B-cell epitopes, and analyzed amino acid variability. Following this, we conducted a comparative analysis with previously published datasets, which revealed new tandem repeat types, new positions of serine within tandem repeats, and high variation among B-cell epitope variants. We have also classified the unique R1 tandem repeats of the new MSP1a sequences into different ecoregion clusters based on the principal component analysis of NDVI values. This updated classification system enhances the molecular understanding of A. marginale diversity and may contribute to future developments in strain typing, epidemiological investigations, and vaccine research.