MSP1a is part of the A.marginale major surface protein 1 (MSP1) complex and exists as a heterodimer with MSP1b. The complex has adhesive functions in bovine erythrocytes invasion [1].

1: Cloning, expression, and characterization of the MSP1a and MSP1b recombinant proteins from PR1 Anaplasma marginale strain, Brazil. Tamekuni K, Kano FS, Ataliba AC, Marana ER, Venancio EJ, Vidotto MC, Garcia JL, Headley SA, Vidotto O; Res Vet Sci. 2008; [Epub ahead of print] PMID:18603273

2: Analysis of world strains of Anaplasma marginale using major surface protein 1a repeat sequences. de la Fuente J, Ruybal P, Mtshali MS, Naranjo V, Shuqing L, Mangold AJ, Rodriguez SD, Jimenez R, Vicente J, Moretta R, Torina A, Almazan C, Mbati PM, de Echaide ST, Farber M, Rosario-Cruz R, Gortazar C, Kocan KM; Vet Microbiol. 2007;119:382-390. PMID:17084044